Select

2012, 31 (S1): 0-

[PDF] 552 KB (36)

+

Show Abstract

Select

IMPROVED CWFS MODEL FOR HARD ROCKS AND ITS APPLICATION TO STABILITY ANALYSIS OF HIGH ROCK SLOPE

QIAO Lan1，2，GAO Wen1，2，LI Yuan1，2，YANG Zhijun1，2

2012, 31 (S1): 2593-2600

[PDF] 1229 KB (19)

+

Show Abstract

Continuum models with traditional failure criteria(e.g. Mohr-Coulomb criterion) based on simultaneous mobilization of cohesion and frictional strength components cannot successfully predict the extent and depth of brittle failure of surrounding rocks in tunnels，while the cohesion weakening-friction strengthening(CWFS) model，rarely used in stability analysis of high rock slopes，has a good application prospect in engineering. Firstly，the CWFS model and its improved editions were discussed. Then the CWFS model was modified to be the cohesive losing and frictional mobilizing(CLFM) model according to the particular mechanical behaviors of hard rocks in low confinement conditions. Finally，the CLFM model was applied to the stability analysis of a hard rock slope，and the results were compared to those obtained by the Mohr-Coulomb criterion. It is demonstrated that the slope is still in a stable condition. Both the displacement and plastic zone at the foot of the slope are underestimated while the stress level is overestimated by the Mohr-Coulomb criterion. Furthermore，the displacement of slope under actual in-situ stresses is 10 times that under gravity stress field only.

Select

MOVEMENT PROCESS SIMULATION OF HIGH-SPEED LONG-DISTANCE JIWEISHAN LANDSLIDE WITH PFC3D

ZHANG Long，TANG Huiming，XIONG Chengren，HUANG Lei，ZOU Zongxing

2012, 31 (S1): 2601-2611

[PDF] 6315 KB (30)

+

Show Abstract

The particle flow code in three dimensions(PFC3D) is adopted to simulate the movement process of Jiweishan landslide in Wulong County，Chongqing City. The movement process of landslide mass along the sliding surface is studied under the gravity and apparent sliding force after instability of key blocks. The following conclusions can be drawn. (1) For large long-distance landslides，if the morphology of sliding surface along the landslide movement path is determined，the friction coefficient of sliding surface and strength of sliding mass just significantly affect the distribution of sliding mass in deposited areas；and the micro-topography would have more influences on the maximum displacement of landslide. (2) The whole process of the high-speed long-distance Jiweishan landslide can be divided into two stages. The first stage is mainly the fragmentation of rock masses in source area，and the second stage is the movement and run-out of fragmental blocks. (3) It is found that the velocity of blocks in surrounding regions of sliding mass firstly reaches the maximum according to velocity and displacement monitored in field. The blocks have the characteristics of second acceleration. Combining the velocity and displacement，it is considered that the sliding body at the upper edge of sliding mass is more likely to move for a long distance. (4) For Jiweishan landslide，when the friction coefficient of sliding surface is 0.05 and the bond strength is medium(250–200 MPa)，the results obtained by PFC3D are in accord with the actual ones in the maximum degree. For such high-speed long-distance landslides，PFC3D has a good applicability，especially its three-dimensional deposition state and influential extent initially identified could provide useful references for disaster prevention and mitigation works such as determination of safe avoidance range.

Select

Research ON DDA method for RESPONSE OF SLOPES UNDER EXCAVATION AND DYNAMIC LOAD

FU Xiaodong，SHENG Qian，ZHANG Yonghui

2012, 31 (S1): 2612-2618

[PDF] 1249 KB (13)

+

Show Abstract

Discontinuous deformation analysis(DDA) method is improved to analyze the response of slopes under excavation and dynamic load. Firstly，the process of slope excavation is simulated using the DDA method based on element birth and death，and the deformation of slope is analyzed. The results are compared to those of finite element method. It is indicated that the DDA method is effective in slope simulation. Secondly，the input way of seismic wave is carried out based on viscous boundary theory. It is better than the traditional DDA method because the traditional DDA method does not consider the reflection of scattered waves at boundaries，which are generated in the media. In addition，the free-field boundary is introduced into the DDA method. Case study shows that DDA model with free-field boundaries at both sides is better than that with viscous boundaries. Finally，the improved DDA method is used to analyze the response of slopes under dynamic load. By comparing the results with those of finite element method，the accuracy of the improved DDA method is proven.

Select

ANALYSES OF CRITICAL SLIDING DISPLACEMENT OF LANDSLIDE INDUCED BY STRONG EARTHQUAKE IN MOUNTAINOUS AREA

QIAN Haitao1，ZHANG Lifang1，LAN Jingyan1，WANG Sijing2

2012, 31 (S1): 2619-2628

[PDF] 815 KB (13)

+

Show Abstract

The permanent sliding displacement of a landslide induced by strong earthquakes is a metric parameter of stability and a state parameter of landslide system，and the transient deformation caused by seismic oscillation is equivalent to the random fluctuation of landslide system. Thus，in a landslide system，its potential energy lies on the permanent sliding displacement of slip mass，which can represent the stability state of the landslide system. At the same time，the potential energy is independent of specific vibration process of slip mass. Substantially，the critical sliding displacement corresponds to the catastrophe point of the system potential energy. So the problem of determining the critical sliding displacement can be converted to finding the catastrophe point of potential energy. A cusp catastrophe model is set up based on the geological and mechanical models of earthquake-induced landslides in mountainous area. Then the criterion for instability of landslides and methods for determining the critical sliding displacement are proposed，and the application condition of the criterion is discussed. It is found that the critical sliding displacement is related to the geometrical and mechanical characters of sliding zone and deadweight of slip mass，but has no relation with seismic wave. The critical sliding displacement can be treated as the stability criterion of a landslide conditionally. And it should be pointed out that the basic factor leading to sliding lies on the relative inertial force originated from the relative acceleration between the slip mass and base rock，and the way of applying the acceleration recorded by a strong motion seismograph to the slip mass directly is inappropriate.

Select

BLASTING VIBRATION TESTS AND ANSYS TIME-HISTORY ANALYSES OF SLOPE RESPONSES

XU Mingbiao1，2，PENG Dehong2

2012, 31 (S1): 2629-2635

[PDF] 800 KB (41)

+

Show Abstract

The dynamic responses of high steep rock slopes are complex under blasting，which are commonly analyzed by combining field blasting vibration tests with ANSYS time-history analyses. A slope was analyzed using this method to investigate the influence of blasting vibration on slope stability and to find out the dynamic response rules of slope under blasting excavation. Analyses of blasting vibration tests show that vibration velocity may be magnified along elevation for high steep rock slopes when the blasting scale is large. Blasting methods without or with little amplification effect should be adopted to reduce the vibration and increase the dynamic stability of the slope. ANSYS time-history analyses show that：(1) The values of stresses are small but stress concentration occurs；(2) The nodal displacements are small and no plastic deformation happens in the slope；(3) The simulated values of velocity is consistent with the measured ones；(4) If only the dynamic effect of blasting is considered，the slope will not fail wholly；(5) As the blasting scale increases，obvious velocity amplification effect and inertia hysteresis effect happen. (6) The dynamic stress，displacement and velocity simulated by ANSYS can reflect the dynamic response characteristics of the slope well. The results of numerical simulations accord well with field testing results，providing guidance to similar projects.

Select

CALCULATION MODEL OF IMPACT ENERGY BASED ON INTERACTION OF LANDSLIDE MASS AND DISASTER-AFFECTED BODIES

WU Yue1，LIU Dongsheng2，LI Shuoyang3

2012, 31 (S1): 2636-2643

[PDF] 1540 KB (16)

+

Show Abstract

Impact energy is an important basis for landslide vulnerability assessment. Internal collapse of landslide mass dissipates part of the kinetic energy in the process of landslide. Calculation equations of impact energy are proposed based on the study of interaction mechanism between landslide mass and disaster-affected bodies. Based on the equations，a simplified model for impact energy calculation is put forward. At the same time，a coefficient of impact effect is defined，which can reflect the impact energy intuitively. The coefficient of impact effect indicates that the impact energy and internal energy dissipation of landslide mass are determined together by the characteristics of landslide and disaster-affected bodies. Increment in the coefficient of impact effect means that the impact energy decreases and the internal energy dissipation of landslide mass increases；and vice versa. The results of case study show that the impact energy calculated by the simplified model is consistent with those obtained by experiments，and it is more accurate than the result calculated by the method without consideration of the internal energy dissipation.

Select

CENTRIFUGAL MODEL TEST OF SLOPE REINFORCED BY SMALL-DIAMETER STEEL PIPE ROW PILES

XIANG Bo1，2，MA Jianlin1，HE Yunyong1，ZHU Lin1，ZHANG Zhengyi1

2012, 31 (S1): 2644-2652

[PDF] 2577 KB (32)

+

Show Abstract

As a new retaining structure，the small-diameter steel pipe anti-sliding pile is used extensively for slope reinforcement and landslide control，but its some behaviors，such as anti-sliding characteristics，force mechanism and failure mode，etc.，need to be further studied. Combining with a specific engineering，centrifugal model tests of small- diameter steel pipe row piles are used to investigate the effects of slope failure mode，stress condition，pile spacing and connection beams on slope anti-sliding capacity. The results show that the model slope in each group suffers overall structure failure，and sliding surface can be observed clearly only in slopes without reinforcement. The anti-sliding mechanism of this kind of structures represents the geological improvement by high-pressure grouting and cooperative anti-sliding activity by piles and rock-soil composite structure. The main failure mode of this kind of structure is overall instability caused by axial tension and compression. The anti-sliding capacity of row piles is affected dramatically by pile spacing. The relationship between the ratio of pile spacing to pile diameter(L/) and factor of safety of slope is a power function，and the value of L/ of this type of row piles is recommended to be 6–12. Soil pressures behind piles increase with the increasing depth first and then decrease，and they approximately present a triangular distribution above the sliding surface. For the triple-row pile structure with connection beams，the bearing capacity of pile B decreases with the increase of acceleration，while that of pile C is on the contrary. The factor of safety of slope increases by 38.3% under the action of connection beams.

Select

SPATIAL PREDICTION OF LANDSLIDE HAZARDS IN NEW SITE OF BADONG COUNTY BASED ON SET PAIR ANALYSIS

GUI Lei，YIN Kunlong，LIU Changchun

2012, 31 (S1): 2653-2659

[PDF] 1504 KB (13)

+

Show Abstract

Set pair analysis(SPA) method has a certain important theoretic significances and practical applications to landslide spatial prediction. Landslide prediction system is always affected by uncertainties that the SPA method can resolve based on the platform MAPGIS. Firstly，the geological setting in the new site of Badong County is counted and prediction units are divided. Secondly，risk assessment criteria are determined and index levels of all the predicted units are discriminated according to unit properties. Thirdly，risk level of each unit is predicted based on the SPA method. The results are considered feasible and reliable by comparing the predicted spatial distribution of landslide with the known landslide hazard map. It is shown that the contact degree and set pair potential theory can improve prediction accuracy.

Select

APPLICATION OF RELIABILITY THEORY TO BACK ANALYSIS OF ROCKY SLOPE WEDGE FAILURE

SUN Lichuan1，WANG Hongxian1，ZHOU Nianqing2，NING Baoyi1

2012, 31 (S1): 2660-2667

[PDF] 1097 KB (28)

+

Show Abstract

The method of back analysis targeted on factor of safety and failure probability is introduced on the basis of reliability theory. According to the limit state function of wedge failure，Monte Carlo method is applied to back analysis of wedge failure of foundation pit slope in a nuclear power engineering. The limit state of failure slope is represented by failure probability. It is found that the back analysis method targeted on failure probability is more proper and reasonable than that targeted on critical factor of safety，for the latter has some deficiencies. Combined with case study，the effects of variation factor of cohesion and internal friction angle，truncated location，and correlation coefficient on the results of back analysis are discussed. The results show that the shear strength of structural surface obtained by back analysis is more realistic，and it can guide engineering practices.

Select

DISTRIBUTION OF LANDSLIDE THRUST ON CANTILEVER DOUBLE-ROW ANTI-SLIDING PILES

SHEN Yongjiang1，2，SUN Hongyue2，SHANG Yuequan2，HUANG Li1，YAN Kewu3

2012, 31 (S1): 2668-2673

[PDF] 606 KB (13)

+

Show Abstract

Double-row anti-sliding piles are often used in large-scale landslides. Cantilever double-row anti-sliding pile is a common type. Firstly，the optimal state of the cantilever double-row piles was assumed，and the mechanical transfer process of the cantilever double-row piles was analyzed. Then，based on the soil arch theory and the limit equilibrium theory，the formulas of landslide thrust loaded on the front and rear row piles were derived，and the method for calculating the distribution of landslide thrust was proposed. Finally，the calculation method was used to calculate the landslide thrust on the cantilever double-row anti-sliding piles of the landslide K103 along Hangzhou―Jinhua―Quzhou expressway. The theoretical results were consistent with the monitoring results. Thus，the correctness and applicability of the method were verified. This calculation method could be useful for the design of cantilever double-row anti-sliding piles. In the design of cantilever double-row anti-sliding piles，it is suggested to calculate the landslide thrust distribution firstly，and then to conduct structure design.

Select

EFFECT OF GEOLOGICAL STRUCTURES ON IN-SITU STRESS DISTRIBUTION IN UNDERGROUND COAL MINES

KANG Hongpu1，2，WU Zhigang1，2，GAO Fuqiang1，2，JU Wenjun1，2

2012, 31 (S1): 2674-2680

[PDF] 937 KB (8)

+

Show Abstract

Using the hydraulic fracturing in-situ stress testing rig with small boreholes，stress measurements were carried out at 14 sites near the large syncline structure in the Huating coal mining area，where steep and extremely thick coal seams are typical in China，to analyze the in-situ stress variation in different parts. Measured data point out that the tectonic stress predominates in the Huating coal mine and Yanbei coal mine. Along the wing of the syncline structure，the horizontal stress is comparatively small；however，the horizontal stress near the axis of the syncline structure increases far more quickly than the vertical stress；and the syncline structure greatly influences the stress distribution in the coal mining area. Based on the in-situ stress data measured in the Jincheng coal mining areas in Shanxi Province，the effects of faults on the magnitude and orientation of in-situ stresses were analyzed. Some areas near the faults show the lower horizontal stress than the normal level，and large faults may alter the orientation of the maximum horizontal principal stress. On the basis of measured in-situ stresses，numerical models were built to analyze the stress distribution around the large syncline structure in the Huating coal mining area by means of FLAC3D code，and the numerical results were compared with the measured ones. The combination of in-situ stress measurement and numerical simulation will provide an effective approach to fully understand the characteristics of in-situ stress field in underground coal mines.

Select

Study oF construction characteristics and dynamic behavior of deep clay stone during shield tunneling under seepage-stress coupling effect

JIA Shanpo1，2，3，CHEN Weizhong2，3，YU Hongdan3，LI Xiangling4

2012, 31 (S1): 2681-2691

[PDF] 4700 KB (11)

+

Show Abstract

Based on the theory of large deformation and damage mechanics，an elastoplastic coupling analysis model considering effect of large deformation is set up by introducing damage evolution and seepage-stress coupling into the Mohr-Coulomb criterion. An equivalent layer model is adopted after comprehensive analysis of surrounding rocks associated with shield tunneling. Considering the actual case of construction of connecting gallery of a radioactive waste disposal in the deep Boom clay formation in Belgium，different tunnel construction qualities are calculated by small deformation，large deformation，respectively，by the secondary development of ABAQUS. The distributions of pore pressure，plastic strain and deformation around the tunnel associated with shield tunneling are analyzed in details. The results show that the deformation of surrounding rocks reaches the maximum in the vicinity of the excavation face and tunnel construction quality affects the stability of surrounding rocks significantly. This study is useful for shield tunnel construction and field measurement.

Select

SHEAR BEHAVIORS OF INTERLAYER STAGGERED ZONE AT BAIHETAN HYDROPOWER STATION

XU Dingping1，FENG Xiating1，CUI Yujun2，JIANG Quan1，Jiang Yali3，HUANG Ke3

2012, 31 (S1): 2692-2703

[PDF] 1241 KB (14)

+

Show Abstract

Based on the results of in-situ direct shear tests and laboratory shear tests on interlayer staggered zones at Baihetan hydropower station，the shear behaviors of interlayer material and interlayer material/host rock interface(soil/rock interface) were investigated. It is observed that both of interlayer material and soil/rock interface show an elastic perfect-plastic behavior without dilatancy. Creep of interlayer material is found to be insignificant. The interface roughness dependent of shear strength of soil/rock is identified，namely，the rougher the interface is，the higher the shear strength is. A comparative analysis was performed based on the shear strength parameters from in-situ and laboratory direct shear tests on the interlayer material. It is evidenced that the heterogeneity of samples is significant under both laboratory and field conditions. The sampling disturbance seems to be a factor less important compared to the sample heterogeneity. The size effect is evidenced by the larger internal friction angle obtained in laboratory on small samples than that obtained in the field on large samples. The clay fraction is found to be an important factor，and its increase reduces the internal friction angle and increases the cohesion. Despite the significant data scatter，the effect of initial degree of saturation is identified to be negligible. A good consistency is observed by the comparison of the results from the field tests with those from the laboratory tests in terms of effects of clay fraction and initial degree of saturation，indicating that sample size and sample variability are secondary factors that influence the shear strength of interlayer material.

Select

ANALYSES OF surrounding rock stability OF CAVERN GROUP AND SEEPAGE FIELD AT DALIAN UNDERGROUND OIL STORAGE

YU Chong1，LI Haibo1，ZHOU Qingsheng2

2012, 31 (S1): 2704-2710

[PDF] 1995 KB (14)

+

Show Abstract

Aiming at analyses of surrounding rock stability of cavern group and seepage field characteristics at Dalian water-tight underground oil storage，firstly，based on regression analysis of in-situ stress testing data，initial in-situ stress field inversion is conducted with functions defined with program language Fish. Secondly，after three-dimensional random joint networks with different sizes are generated with 3DEC，a new method of calculating the anisotropy permeability is proposed. Finally，stress field and displacement field of surrounding rocks are gained using coupled fluid and mechanical excavation calculations. Based on point safety factor，whose criterion is the Mohr-Coulomb one with the tensile strength，cavern group stability is quantitatively evaluated considering parallel and vertical bedding planes owing to different materials characteristics. Referring to ideas from abroad，seepage field is analyzed by groundwater table and vertical hydraulic gradient，respectively. Results indicate that point safety factor is 1.95–2.00 for the materials in the direction perpendicular to bedding planes，while 1.02–1.25 in the direction parallel to bedding planes. With the artificial water curtain system comprised of water tunnels and holes，the groundwater drops 3–5 m during construction period，and the distance between groundwater table to cavern crown is 55 m. The average vertical hydraulic gradient is greater than 1.0 around the caverns，which meets the design specification and sealing requirement.

Select

REINFORCING MECHANISM AND SIMULATING METHOD FOR REINFORCING EFFECTS OF SYSTEMICALLY GROUTED BOLTS IN DEEP-BURIED HARD ROCK TUNNELS

WU Wenping1，2，FENG Xiating1，ZHANG Chuanqing1，QIU Shili1，LI Zhanhai3

2012, 31 (S1): 2711-2721

[PDF] 2499 KB (26)

+

Show Abstract

Systematically grouted bolts，as the main support structure of deep-buried hard rock tunnels，compose the bolt-rock composite structure with surrounding rocks，which reinforces the mechanical property of surrounding rocks. Based on the Mohr-Coulomb(M-C) criterion，the stress condition and the strength of the composite structure meeting the M-C criterion were derived under high-stress conditions. Combining with the rock mass deterioration model(RDM) of brittle rock，an approach to determine the mechanical parameters of the composite structure was presented. The difference of mechanical parameters between two different composite structures of bolt-elastic surrounding rock and bolt-yielding surrounding rock was taken into account. In this approach，the mechanical parameters of the bolt-yielding surrounding rock composite structure were associated with present equivalent plastic strain of surrounding rocks. A numerical method，which could model the reinforcing effect of normally grouted bolts laid out systematically during excavating and supporting stages，was proposed. It is identified that this method has an advantage over other methods in modeling the effect of supporting time on surrounding rock stability. Finally，the method was applied to evaluate the stability of surrounding rocks，and related references were provided for design and construction of the diversion tunnel #2 of Jinping II hydropower station.

Select

INTERNAL VARIABLE GRADIENT PLASTICITY MODEL FOR ZONAL DISINTEGRATION OF SURROUNDING ROCKS IN DEEP TUNNELS

QI Chengzhi 1，QIAN Qihu2，WANG Mingyang2，CHEN Jianjie3

2012, 31 (S1): 2722-2728

[PDF] 432 KB (14)

+

Show Abstract

In plastic deformation regime，energy dissipation and self-organization phenomenon take place in rock masses surrounding tunnels，and the long-range interaction between rock particles becomes significant. Therefore，the term of internal variable gradient should be added to the constitutive model of rock masses. Gradient of effective plastic strain is introduced as an additional internal variable. Equilibrium equations and boundary conditions are derived by using the virtual work principle. Evolutionary equations for internal variables of rock masses are obtained by using the Clausius-Duhem inequality. For circular deep tunnels，the governing equation for effective plastic strain is obtained from the above model. Solution to the governing equation for ideal brittle model of rock masses is achieved. The solution may describe zonal disintegration phenomenon very well.

Select

ARCH SPRINGING STABILITY AND ITS CONTROL techniques DURING CONSTRUCTION of tunnels with weak surrounding rocks BY BENCH CUT METHOD

LI Wenjiang1，2，SUN Minglei1，ZHU Yongquan1，ZHU Zhengguo1，LI Yuliang3

2012, 31 (S1): 2729-2737

[PDF] 2070 KB (25)

+

Show Abstract

Taking a railway tunnel as background，combining with numerical analysis method and in-situ tests， the deformation characteristics of arch springing and destabilization mode of surrounding rocks during construction of the tunnel by bench cut method were analyzed. In addition，corresponding control measures for arch springing stability were discussed. The following results are achieved. (1) During the construction of tunnel，the settlement and horizontal convergence of arch springing are notable. Therefore，the control of arch springing deformation is one of the key measures to prevent the occurrence of large deformation of weak surrounding rocks. (2) The high yield degree of surrounding rocks at arch springing is one of the prime reasons for large deformation of arch springing. During the construction of tunnel by the bench cut method，damage forms of bedrock at foundations change from local destabilization of arch springing to integral shear failure with the increase of bench height. (3) Based on the control effects of arch springing deformation，the section of tunnel with the surrounding rock of class IV can be excavated by long bench cut method，the section with the surrounding rock of class V should be excavated by short bench cut method，and for the section with the surrounding rock of class VI，the micro-bench cut method is recommended. (4) For tunnels with weak surrounding rocks，proper bench height increment is beneficial to the stability of surrounding rocks under the condition that the working face stability is ensured. (5) The techniques of widening arch springing and setting temporary inverted arch are of obvious effects for controlling the deformation of arch springing. But the technique of widening arch springing is suitable for projects where arch settlement is remarkable，and the temporary inverted arch technique is more applicable to the sections with remarkable horizontal convergences.

Select

SEEPAGE FIELD-STRAIN FIELD COUPLING ANALYSIS FOR ROCK MASSES OF coal SEAM FLOOR DURING MINING ABOVE A CONFINED AQUIFER

YAO Duoxi1，LU Haifeng2

2012, 31 (S1): 2738-2744

[PDF] 2107 KB (19)

+

Show Abstract

Based on the geological and hydrogeological conditions of the face 1018 in Wugou coal mine，the fluid-solid coupling module in FLAC3D with changeable permeability coefficient is adopted to simulate the whole process of damage and failure of rock masses at floor of the coal seam No.10. The results indicate that the permeability coefficient of surrounding rocks changes a lot due to mining. The maximum permeability coefficient reaches 1 293 times of the original one，which happens at the immediate roof of mined-out area. According to the analysis of seepage field，mining does not destroy water resistance of floor aquifer. Mining fissures do not connect limestone aquifers，and water in the limestone is less likely to flow into stopes to cause damage. The maximum depth of rock masses with element safety degree less than one is about 30 m. According to the change of permeability coefficient of and the analytical results of element safety degree of rock masses，safe mining of the face 1018 can be ensured.

Select

RELATIONSHIP BETWEEN FRACTAL DIMENSION OF SECTION PROFILE AND JOINT PARAMETERS OF TUNNEL SURROUNDING ROCKS

ZHANG Peng1，2，CHEN Jianping1，ZHANG Li3，XIAO Yunhua4

2012, 31 (S1): 2745-2750

[PDF] 788 KB (14)

+

Show Abstract

The stability of lining structure is influenced by under-excavation and over-excavation of tunnels. It is of great significance to understand the surrounding rock stress and ensure construction safety by studying the over-excavation and under-excavation rules of tunnels. Based on the multi-scale function of wavelet analysis and the statistical self-similarity between the over-excavation and under-excavation of tunnel section profile，the fractal dimensions of 47 tunnel section profiles were calculated by the wavelet analysis. According to the statistical data of joint parameters obtained by field investigation，relationship between the fractal dimension of section profile and joint parameters of tunnel surrounding rocks was analyzed. A function for evaluating the stability of tunnel surrounding rocks was established. With the increase of the fractal dimension，the stability of surrounding rocks gets worse. As the angle between the tunnel axis and joint strike and the over-excavation percentage increase，the fractal dimension of section profiles decreases. When the joint space increases from 0.25 to 0.40 m，the fractal dimension of section profile also decreases.

Select

Geological structures and MECHANICal ANALYSIS OF LARGE- DEFORMATION MUD BURSTING SECTION IN YANMENGUAN TUNNEL

LIN Daming1，2，SHANG Yanjun1，CHEN Mingxing3，QIAO Guanghong4，WANG Kaiyang1，2

2012, 31 (S1): 2751-2757

[PDF] 1877 KB (64)

+

Show Abstract

Yanmenguan tunnel is located in the Hengshan metamorphic area，which is controlled by strike-slip structures. During construction，large deformation and sudden mud bursting often happened，especial in the section of DK118+30.0–DK118+200.0. Based on analyses and numerical simulations of bias pressure feature of strike-slip faults，and monitoring of stress and deformation，it is found that：(1) The section of DK118+30.0–DK118+200.0 is controlled by the strike-slip structures. (2) The dominant factor for bias pressure of deep tunnel is the difference of surrounding rock class，and the bias pressure affects the subsidence of surrounding rocks obviously. (3) The failure mechanism of surrounding rocks of Yanmenguan tunnel is interlayer shear and compression. It is suggested that the stress of surrounding rocks and the difference in rock properties should be considered during design and construction of tunnels in metamorphic area，and construction technologies should be accordingly changed.

Select

RESEARCH ON ROCKBURST MECHANISM AND PROFILE SUITABILITY OF DEEP-BURIED TUNNEL IN FOLD STRUCTURE BODY

GUO Changbao1，2，ZHANG Yongshuang1，JIANG Liangwen3，SUN Dongsheng1，

2012, 31 (S1): 2758-2766

[PDF] 3271 KB (60)

+

Show Abstract

Geological structures have some important effects on rockbursts. Taking the deep-buried Gaoligong Mountain tunnel for example，based on field geological investigation，laboratory rock mechanical tests and geostress measurements，adopting the finite element software ANSYS，stress redistribution of the tunnel surrounding rocks，which is induced by tunnel excavation，is analyzed under current geostress. The rockburst characters of the tunnel are also deeply investigated under different case combinations，and possible rockburst positions and intensity are predicted. The results indicate that the rockburst intensity has some relations with the position in the geological structure body where the tunnel is located，as well as the tunnel profile. Namely，the rockburst is prone to happen mostly when the tunnel axis is parallel to the fold axial line and the horseshoe tunnel is located at synclinal-shaft，or the circular arch-vertical wall tunnel is located at the anticlinal-shaft and fold limb department；but when the tunnel axis is vertical to the fold axial line，the possibility of rockburst is small. During tunnel planning and construction，the position where the tunnel axis is vertical to the fold axis，or more suitable tunnel profile，should be selected，which is advantageous for weakening the influence of rockbursts.

Select

DEFORMATION STOCHASTIC ANALYSIS OF TUNNEL SURROUNDING ROCK CONSIDERING ITS SPATIAL RANDOMNESS

CHENG Yonggang1，2，CHANG Xiaolin1，2，LI Dianqing1，2

2012, 31 (S1): 2767-2775

[PDF] 3339 KB (8)

+

Show Abstract

The design of tunnels requires a proper estimation of deformation of surrounding rocks or soils. Popular simulation approaches in engineering practice are deterministic，in which the variability of rock masses is not considered. However，numerous studies have shown that the generally large variability of rock properties may have big influences on the simulation results. The effect of spatially variable rock properties is assessed via numerical experiments using a non-intrusive stochastic finite element analysis scheme，in which the rock properties are modeled as homogeneous random fields. The non-intrusive scheme means that there is no need for user-intervention during the calculation of the deterministic finite element code while the normal stochastic finite element methods always do. Observations show that the randomness of in-situ horizontal stress coefficient is much less important as the Youngs modulus. From the average maximum surface deformation，it would appear that the characteristic modulus is not a simple arithmetic average，but one that favors low modulus pixels with a higher weight. The uncertainties in the ground movements are controlled by some local averaging of the Youngs modulus in both directions.

Select

STUDY OF CONSTRUCTION TECHNOLOGY FOR SUBSURFACE EXCAVATION OF METRO TUNNEL GROUP IN COMPLEX ENVIRONMENT

DUAN Baofu1，2，LI Lei1，2

2012, 31 (S1): 2776-2782

[PDF] 3391 KB (8)

+

Show Abstract

The lines No.5 and No.7 of Shenzhen metro are designed as double-tube overlapped two-storey tunnels from Taian Station to Yijing Station. The upper and lower tunnels are staggered for a certain distance and then excavated synchronously in construction process. Due to the complex environment and relatively poor geological condition，advanced small pipes grouting with cement-water glass(CS) is supplemented for water-seal and reinforcement. According to different cross-sections of tunnels，reasonable construction technologies are selected to reduce the disturbance to soils. These measures improve the construction environment effectively，ensures the safe construction of the project，and shortens the construction period greatly. This project can porvide reference values to similar domestic projects.

Select

LARGE DEFORMATION MECHANISM ANALYSIS OF SURROUNDING ROCKS IN DEEP UNDERGROUND CAVERN DURING CONSTRUCTION

FEI Wenping1，2，ZHANG Jianmei1，2，CUI Huali1，2，ZHANG Guoqiang1，2

2012, 31 (S1): 2783-2787

[PDF] 1049 KB (12)

+

Show Abstract

The underground caverns of Dagangshan hydropower station show typical characteristics of large buried-depth，strong weathering of surrounding rocks，full development of dike and fractures，and high in-situ stresses. During construction，the deformation of transformer chamber where dikes and faults cross through is very significant，which seriously affects the safety and advance of construction. On the basis of geological investigation and field monitoring，according to the field construction condition，the large deformation mechanism of surrounding rocks is analyzed. Two possible large deformation failure modes are proposed. Factors inducing large deformation are analyzed，and the stability of transformer chamber is evaluated. The results show that the large deformation of surrounding rocks is mainly controlled by diabase dike and faults f59，f60. The high in-situ stresses，high intensity of construction and delayed supporting accelerate the large deformation of surrounding rocks. The geological investigation and field monitoring are very useful for forecasting the large deformation of unloading rocks in high stress zones，and for ensuring the stability and safety of underground cavern during construction. The results have very important reference values for similar projects.

Select

RESEARCH ON PERMEABILITY OF FRACTURED ROCK

YU Hongdan1，CHEN Feifei2，CHEN Weizhong1，3，YANG Jianping1，CAO Junjie1，YUAN Kekuo1

2012, 31 (S1): 2788-2795

[PDF] 744 KB (9)

+

Show Abstract

The fractures existed in the rock mass influence the rock permeability significantly. In order to study the impact of different loadings on the permeability of fractured rock，a series of loading and unloading seepage tests were carried out on fractured sandstone and siltstone samples using the high-precision hydro-mechanical coupling test system. The test results show that：(1) Permeability decreased as well as the aperture of the fracture as the inflow pressure increased during the loading tests. (2) The permeability recovered gradually as the hydrostatic pressure decreased during the unloading procedures，but the recover path is lower than the original path. It shows that plastic deformation has occurred for the fractures. Based on the test results，the relationship between permeability and effective confining pressure was established. Moreover，based on the experiments and theory，the permeability and seepage velocity variation of the fracture surface was analyzed through numerical simulation.

Select

ANALYSIS OF SHEAR RHEOLOGICAL MECHANICAL PROPERTIES OF FUCHSIA MUDSTONE

HU Bin，JIANG Haifei，HU Xinli，GUO Lina，WANG Xingang

2012, 31 (S1): 2796-2802

[PDF] 672 KB (67)

+

Show Abstract

In view of the fuchsia mudstone in the No.2 landslide of Wulidui，the laboratory shear rheological test is carried out to research rheological characteristics in the mass shear process. Five-component viscoelastic shear rheological model is selected to establish shear rheological equation，and Origin tool function Exp Assoc is used to fit the fuchsia mudstone test curves which have viscoelastic property；then the viscoelastic rheological parameters are determined. At the same time，the parameters are used to analyze the rheological curves deeply. Based on the shear rheological experiment of fuchsia mudstone，the long-term shear strength parameters are determined. Compared with the instant shear strength parameters，the long-term shear strength parameters have been reduced to some extent. Therefore，using the long-term shear strength parameters to design landslide project is more reliable to guarantee the project security.

Select

COORDINATION SUPPORT SYSTEMS IN MINING WITH FILLING AND MECHANICAL BEHAVIOR

YU Weijian1，2，FENG Tao1，2，WANG Weijun1，2，LI Shilin1，2

2012, 31 (S1): 2803-2813

[PDF] 870 KB (42)

+

Show Abstract

Aiming at subject of strata movement and control caused by the mining with filling under buildings，railways and water-bodies(three-underground)，achieving together action of backfilling，coal pillar and roof load-bearing rock stratum was emphasized，and the conception of coordination support systems is put forward. Rock mechanics，strata control principle and others correlation theory are applied to analyze the supporting mechanism of backfilling，the supporting conditions of coal pillar and the process of mechanics action and the stability condition of the coordination support systems. Research shows that the supporting mechanism of backfilling act as the horizontal reinforce action at coal pillar and the vertical supporting action at roof load-bearing rock stratum；the horizontal reinforce action should meet the controlled condition for the purpose of greater holding power which coal pillar effect on overburden；The mechanics action of the coordination support systems with backfilling，coal pillar and roof load-bearing rock stratum experience four main stages including the accelerated subside of overburden，uniform speed subside，decelerated subside and steady in proper order. Moreover，it is found that the degree of compaction(Dr) and the packing fraction(Ff) bigger，these have more advantageous to integrity and bearing strength environment of the coordination support systems，and strata movement and ground subsidence can control as much as possible. At last，the coordination support systems theory is applied in the three-underground mining with filling of Zhouyuanshan mine. In order to reduce ground subsidence as much as possible，analytic result indicated that the degree of compaction(Dr) of backfilling raise to above 0.8，and the packing fraction(Ff) control above 90%.

Select

STUDY OF DYNAMIC FAILURE PROCESSES AND MECHANISM OF ROCK SUBJECTED TO COUPLING TEMPERATURE AND PRESSURE

YIN Tubing1，2，LI Xibing1，2，GONG Fengqiang1，2，ZHOU Zilong1，2，GAO Ke1，2

2012, 31 (S1): 2814-2820

[PDF] 914 KB (49)

+

Show Abstract

Coupling temperature and pressure exist in deep rock generally. Laboratory experiments and numerical simulation have been conducted to study mechanics and failure character of rock subjected to coupling temperature and pressure. The dynamic failure process of rock samples subjected to coupling temperature and pressure are investigated. The numerical simulation reproduces variation of rock failure properties subjected to coupling temperature and pressure. The dynamic failure mode of rock under coupling temperature and pressure and the difference of rock failure characteristics with different temperatures and pressures are found. The results show that the thermal expansion cause producing of rock thermal stress with increased temperatures，and the failure mode is similar to those with different temperatures when the axial pressure is the same. However，there is greater failure degree because of the stress release on samples surface and stress accumulation within samples with increased temperature.

Select

ANALYSIS OF DYNAMIC MECHANICAL PROPERTIES AND MICROCOSMIC RUPTURE OF ANTI-EXPLOSION BUFFER MATERIALS

LU Xiangfeng1，2，PAN Yishan2，XIAO Xiaochun2，3

2012, 31 (S1): 2821-2828

[PDF] 2475 KB (28)

+

Show Abstract

The energy absorption property of closed-cell foam metals with matrix Al，matrix Al-Si12，matrix Al-Si6，matrix Mg，matrix Al-fiber and matrix RE-Al alloys are investigated by the compression，impact and split Hopkinson pressure bar(SHPB) test. And the micro-mechanics failure mechanism of closed-cell foam metals is discussed. Quasi-static experiment results show that the mechanical properties of different foam metals are different，and the maximum of compressive strength is about 5 MPa. Impact test results indicate that the maximum of compressive strength and absorbing energy value are about 15 MPa and 29 J，respectively. The closed-cell foam metals exhibit good energy-absorption ability on the optimal conditions that density is 0.35–0.70 g/cm3，porosity is 65%–87% and pore diameter is 1.0–4.0 mm. The micro-morphology of closed-cell foam metal with matrix Al is obvious tear trace，indicating that it has toughness characteristics. Compared with quasi-static experiment results，closed-cell foam metals with matrix Al is good for energy absorption materials because of its high absorbing energy value and deformation. Similar experimental results show that bolt and U steel support roadway have impact deformation or damage，and the blunt support roadway is better in integrity.

Select

RESEARCH ON SEISMIC DEFORMATION CHARACTERISTICS OF FLEXIBLE WALL

ZHU Hongwei1，2，YAO Lingkan1，LIU Zhaosheng1，CHEN Xiaolong1

2012, 31 (S1): 2829-2838

[PDF] 1605 KB (42)

+

Show Abstract

In order to study the earthquake dynamic response and deformation mechanism of flexible wall，the large-scale shaking table model tests for reinforced gabion wall and reinforced ecological wall were performed. The results showed that the distribution of horizontal peak dynamic earth pressures along height is with large value at both ends and small value at the middle for the two kinds of flexible walls，which is contrary to the distribution of horizontal peak dynamic earth pressures of rigid retaining wall. Due to the bulging deformation under earthquake，the value of horizontal peak dynamic earth pressures of the reinforced gabion wall and reinforced ecological wall is substantially smaller than that of rigid retaining wall. The national standard does take into account the effect of seismic earth pressure attenuation after deformation of flexible wall，the seismic design of flexible wall according to the current standard is conservative. Through analysis，to the flexible wall such as reinforced gabion wall and reinforced ecological wall，in ensuring the seismic stability of the premise，the seismic earth pressures can be reduced properly to save cost. For the seismic design of flexible wall in railway and highway，while maintaining the integral stability of the flexible wall，local-deformation control should be paid attention to too，improving the engineering properties of filling materials and increasing elastic modulus of walling materials as well as thickness of the wall can reduce the displacement of the flexible wall.

Select

CHARACTERISTIC PARAMETERS THEORETICAL ANALYSIS OF ROCKFALL IMPACT ON GROUND

ZHANG Guangcheng1，2，3，TANG Huiming1，2，XIANG Xin3，4

2012, 31 (S1): 2839-2846

[PDF] 835 KB (101)

+

Show Abstract

In accordance with the character of rockfall acceleration or impact force curve，impact force computation theory formulas of front impact are derived using momentum law. Supposing normal impact force is not affected by tangential impact force，a new friction model is proposed，using which tangential impact force and coefficient of restitution both are induced. Finally the change law of impact time，impact force and coefficient of restitution are analyzed when incidence speed，incidence angle or the ratio of the thickness of surface soil to rockfall radius are changed. It showed that：(1) With the impact velocity increasing and the incident angle fixed，the impact force increases linearly，the tangential restitution coefficient ascends with a small amplitude，while the normal restitution coefficient and impact time both descend. (2) With the augment of incidence angle，normal and tangential coefficient of restitution both are getting larger，the increment of tangential restitution coefficient is greater than that of normal restitution coefficient，and the collision time longer，while maximum impact force rise and then drop. (3) With the ratio increase of the thickness of surface soil to rockfall radius，the longer the collision time is，the larger normal coefficient of restitution is while the smaller tangential coefficient of restitution is，and maximum impact force goes up like a concave curve.

Select

SHAKING TABLE TEST STUDIES OF PRESTRESSED ANCHOR CABLE OF SLOPE UNDER EARTHQUAKE

YE Hailin1，2，ZHENG Yingren1，LI Anhong3，DU Xiuli4

2012, 31 (S1): 2847-2854

[PDF] 1188 KB (44)

+

Show Abstract

the large-scale shaking table model test is adopted for study the behavior associated with earthquake shaking of the prestressed anchor cable retaining the slope. Similarity relation is derived by law of gravitivity similitude and dimension analysis method. Three kinds of seismic waves are inputted to study the dynamic response characters of prestressed anchor cable while the amplitudes of input seismic waves are increased. Axial force of prestressed anchor cable and the acceleration and displacement time history are monitored to study the loss of prestress and axial force of prestressed anchor cable subjected to earthquake shaking. Slope stability is also studied. The results show that loss of axial force and prestress of prestressed anchor cable varies with the change of input seismic wave. The maximum value of prestressing loss is 15.7% and with the increment of the peak value of input seismic waves，the prestresssing loss increased at first and then decreased to the critical value while prestressing loss is no longer occurred. It is proposed that the applied prestress value should be 1.1 to 1.2 times of the designed value of the prestress during seismic design of prestessed cable anchor，which is higher than the value under static conditions.

Select

STUDY OF RELATION BETWEEN THERMAL DAMAGE AND LONGITUDINAL WAVE VELOCITIES FOR BUFFER/BACKFILLING MATERIALS

YAN Mingqing1，ZHU Baolong2，YI Facheng1

2012, 31 (S1): 2855-2858

[PDF] 1246 KB (28)

+

Show Abstract

Using of rock mechanics test system，ultrasonic detector，scanning electron microscope and other equipments，the mechanical properties and longitudinal wave velocity of buffer/backfill materials are researched. The results show that below 200 ℃，the slope of stress-strain curve，uniaxial strength of buffer/backfilling materials，increase with increasing temperature. 200 ℃–300 ℃，the slope of stress-strain curve，uniaxial strength of buffer/backfilling materials，uniaxial strength，have varying degrees of decrease. 25 ℃–100 ℃，the average longitudinal wave velocities increase with increasing temperature. 100 ℃–300 ℃，the average longitudinal wave velocities decrease with increasing temperature. Therefore，the relation of longitudinal wave velocity and uniaxial strength are different with properties of buffer/backfill materials.

Select

ESTIMATION OF STRESS VALUE IN 2003 DAYAO SEISMIC SOURCE REGION

WAN Yongge1，XU Xiaofeng2，WANG Huilin2，WAN Di3

2012, 31 (S1): 2859-2866

[PDF] 1147 KB (38)

+

Show Abstract

Using the P wave first motion information of two aftershocks sequence recorded by temporary stations and the new version of grid points test method，we study the stress field in the aftershock zone and get the stress field directions in Dayao region in the two occurrence time periods of the two aftershock sequences. Using the stress value calculation method，we get the underground stress value in the focal area：Before the earthquake，the maximum，intermediate and minimum principal stress is 164.07，158.71 and 153.10 MPa respectively. The normal stress and shear stress projected on fault plane is 157.41，5.24 MPa respectively. The normal stress and shear stress projected on fault plane after the earthquake is 158.69，0.01 MPa respectively. The results show that the pre-seismic shear stress is larger than that of post-seismic，and their difference corresponds to the stress drop approximately. The increasing of normal stress maybe cause the termination of the rupture on the seismic fault. The underground compressive stress is very large，but the differential stress is small. It provide fundamental stress field information for the geodynamic process simulation.

Select

STUDY OF TEMPERATURE FIELD IN PROCESS OF FREEZING-THAWING IN GEOTECHNICAL MEDIUM AND ITS APPLICATION

TAN Xianjun1，YU Xianghong2，CHEN Weizhong1，3，WU Guojun1，YU Hongdan1

2012, 31 (S1): 2867-2874

[PDF] 1228 KB (35)

+

Show Abstract

Basing on the “three-zone”(frozen zone，freezing zone and unfrozen zone) theory，a mathematical model considering the process of freezing-thawing is presented to calculate the temperature field in geotechnical media，the model is verified by correctly simulating the V. J. Lunardini analytical solution for ice formation in a porous medium. Based on this，the influence of heat latent and range of freezing zone on the distribution of temperature in the process of freezing-thawing is studied，and a numerical simulation about a tunnel in Tibet is done to discusses the effect of insulation material. From the numerical results，it is found that the temperature of lining and surrounding rock are greatly changed by building insulation material at the surface of tunnel lining，after constructing a 6 cm thickness poly phenolic insulation，the lining and surrounding rock will not be affected by freezing-thawing damage. The results can give some references for design and construction of tunnel in cold regions.

Select

RESEARCH ON DISTRIBUTION RULE OF GEOSTRESS IN DEEP STRATUM IN CHINESE MAINLAND

LI Xinping1，WANG Bin2，ZHOU Guilong3

2012, 31 (S1): 2875-2880

[PDF] 950 KB (59)

+

Show Abstract

Deeply buried underground engineering often faced with a high geostress environment. Based on the research of the conception of “deep stratum” and “deep engineering”，through collecting about 600 groups of the measured geostress data in deep rocks of China mainland，the distribution of the vertical stress，the largest horizontal principal stress，the minimum horizontal principal stress and the lateral pressure coefficient varying with depth in Chinese mainland are shown in this paper. The features of the geostress in deep rocks are elementarily analysed refer to the analysis method of Hoek and Brown，the distribution rule of the vertical stress，the maximum and the minimum horizontal principal stresses with depth in deep stratum are regressive analysed，and trend of the lateral pressure coefficient with depth is also discussed.

Select

ACCURACY ANALYSIS OF DIGITAL IMAGE PROCESSING SYSTEM FOR TRIAXIAL SPECIMENS WHOLE SURFACE DEFORMATION MEASUREMENT

LIU Xiao1，SHAO Longtan1，GUO Xiaoxia1，HUANG Chuan2，XUE Jie1，YANG Song3，4

2012, 31 (S1): 2881-2887

[PDF] 1691 KB (66)

+

Show Abstract

Possible sources of both system errors and random errors for digital image processing system have been discussed. Calibrations have been made to get ride of system errors such as lens distortion. As for random errors，necessary improvements for experimental environment and data processing have been made. After all these measures taken，other error sources remained are not quantified separately，instead，accuracy of the entire system is examined. Capability of using this system for strain measurement in triaxial tests is illustrated throught comparisons of strain results obtained from both this system and conventional measurement techniques. Finally，the accuracy of this system is quantified through comparison of strain results obtained by both image processing technique and a static strain tester，and the statistical accuracy value is given out to be 4×10－5.

Select

AN EXPERIMENTAL STUDY OF IN-SITU STRESSES OF CARBONATE RESERVOIRS IN TAHE OILFIELD

ZHANG Shicheng1，PAN Linhua1，ZHANG Jin1，MOU Jianye1，ZHANG Ping1，2

2012, 31 (S1): 2888-2893

[PDF] 736 KB (42)

+

Show Abstract

By improving differential strain analysis method，we combine wave velocity anisotropy method and palaeomagnetic core reorientation method to develop a suit of new experimental program on in-situ stresses for small diameter cylindrical cores. Using the new experimental program，we measured magnitude and orientation on in-situ stresses of carbonate cores in the Tahe oilfield in lab. The results show that the orientation of horizontal maximum principle in-situ stress mainly distributes among NE 45°–90°，the gradient of vertical principle in-situ stress is 0.025MPa/m， the gradient of horizontal maximum principle in-situ stress is 0.020 2MPa/m， and the gradient of horizontal minimum principle in-situ stress is 0.015 2 MPa/m，The experimental results are fundamentally consistent with oilfield monitored results. Its indirectly proved that the new experimental program is reliable and practical.

Select

EXPERIMENTAL STUDY OF TEMPERATURE FIELD OF LIQUID NITROGEN FREEZING BY PLASTIC FREEZING PIPE

SHI Rongjian1，2，YUE Fengtian1，2，ZHANG Yong1，2，LU Lu1，2

2012, 31 (S1): 2894-2899

[PDF] 478 KB (45)

+

Show Abstract

The distribution of temperature field，an essential method to judge the frozen ground and to reflect the freezing effect，will be affected when freezing pipes are used in liquid nitrogen freezing of shield tunneling setting out. In order to obtain distribution law of temperature field，the liquid nitrogen freezing model test based on the similarity theory is carried out，which is using plastic freezing pipes in Shanghai mucky clay. Conclusions are drawn as follows：Firstly，the freezing pipe wall temperature is great difference along its longitudinal direction，which will lead to an uneven distribution of frozen wall in different positions. The frozen wall have poor effect in the end of freezing system，where the freezing pipe wall temperature is higher. Secondly，the temperature distribution curve in the frozen region is more steeply than in temperature dropping area. And the temperature gradient in the frozen region of liquid nitrogen freezing by plastic freezing pipe is smaller than in steel tube freezing . Thirdly，the main influence factors of liquid nitrogen freezing effect include liquid nitrogen perfusion status，frozen pipes space and freezing time in the determination soil layer. The advantage of liquid nitrogen freezing can be found in the freezing process，such as accelerating freezing speed，shorting freezing time. The results indicate that the plastic freezing pipe can be used in liquid nitrogen freezing. The conclusion drawn from the study can provide valuable references for the practice.

Select

EXPERIMENTAL RESEARCH ON FREQUENCY CHARACTERISTICS OF ACOUSTIC EMISSION SIGNALS UNDER UNIAXIAL COMPRESSION OF GRANITE

JI Hongguang1，WANG Hongwei1，CAO Shanzhong2，HOU Zhaofei1，JIN Yan1

2012, 31 (S1): 2900-2905

[PDF] 1186 KB (32)

+

Show Abstract

It is significant for us to do some research on AE signal frequency characteristics at different stages in the fracture process in order to select proper AE sensors with corresponding resonant frequencies. Through uniaxial compression test of granite，the result is shown that in the entire compression process，the rock experienced three stages；the ring count presented periodical changing regulation accompanying with the increasing of relative stress，and also the dominant frequencies of AE signals mainly took place at the plastic breaking stage of pre-mainfracture and mainfracture stage，focusing on 41–85 kHz. When relative stress is low，low-frequency signals of granite dominate；With the increasing of relative stress，the low-frequency and high-frequency signals of granite become intensive of which the amplitudes are relatively huge as well. Accordingly，sudden increasing of high-frequency and high-amplitude AE signal predicts potential peril of breaking of granite.

Select

EXPERIMENTAL STUDY OF A NEW COMMENTING MATERIAL USING TAILINGS

YANG Yunpeng，GAO Qian

2012, 31 (S1): 2906-2911

[PDF] 362 KB (66)

+

Show Abstract

This paper makes the new cementing material strength experiment through the uniform design is carried out. This paper applies DPS and Matlab software is applied to strength and formula quadratic multinomial nonlinear regression and optimization. The experiment shows that，in the alkaline environment，sulphate should be added into the slag to arouse its activity to increase its cementation ability. Among the components，slag plays a decisive role in the strength of the cementing material which would have the greatest strength with 76% to 87% slag. At the same time，the compound activator of lime and plaster acts as a catalyst for the strength of the cementing material which would have the greatest strength with 13% to 24% activator. According to the test，the filling strength of new composite material is much higher than that of cement filling，with the number of six to eight times. Using the numerical software，a quadratic polynomial regression formula of 3，7 and 28 days models and strengths was built. In addition，by optimizing the formula，the optimal proportion and the value of greatest compressive strength were acquired.

Select

RELATIONSHIP OF MEASURED VALUES OF STRESS RELIEF METHOD OF EMBEDDED STRAIN GAUGE AND INITIAL STRESS FIELD

CHEN Qu1，WU Dezheng2，XU Jiang3，MIZUTA Yoshiaki1，4

2012, 31 (S1): 2912-2919

[PDF] 932 KB (19)

+

Show Abstract

In the rock stress measurement with stress relief method of embedded strain gauge，both the size of core diameter and the packed thickness of elastic mortar affect the accuracy of measuring precision. In order to discuss the issue，the authors analyzed three cases of stress relief method of embedded strain gauge in secondary stress field，which are over-coring model，practical sensitivity test model and theoretical sensitivity test model. By the comparison of the exact solutions of three cases and calculation of two measurement systems，it could be found that the packing core diameter is not large enough，then measured values of ground stress of rock mass will be significantly underestimated compared with the actual stress field.

Select

ANALYSIS OF STABILITY OF LARGE DEFORMATION ROCK MASS IN RIGHT BANK OF LONGKAIKOU HYDROPOWER STATION

YANG Xiaojie1，2，HAN Qiaoyun1，2，CHEN Xiangxiang3，LIU Jian4，LI Guigang4

2012, 31 (S1): 2920-2925

[PDF] 1577 KB (10)

+

Show Abstract

A large deformation rock mass with a volume of 1 000 m3 is in the right bank of Longkaikou hydropower station，whether it is stable or not can directly affect the construction of the project and its permanent safe operation，so the stability and deformation of the plasmodium needs to be analyzed and studied completely. Using the strength reduction method based on FLAC finite difference，in this paper，the stress-strain relation of the plasmodiums typical section plane III–III is respectively analyzed under the primitive condition and the earthquake circumstance. Studies show that，comparing with the traditional grid limit equilibrium method，this paper can define the distortion pattern of land-side，the plastic yielding area. The study result is of great significance to the stability and the safe operation of Longkaikou Hydropower Hinge.

Select

STUDY OF MONITORING MODEL OF FACED ROCKFILL DAMS DEFORMATION BASED ON PARTICLE SWARM OPTIMIZATION-BP ALGORITHM

LUO Dan1，2，LI Changcai2，WU Changbin3

2012, 31 (S1): 2926-2931

[PDF] 723 KB (10)

+

Show Abstract

A dam safety monitoring model is presented by combining a BP neural network algorithm and particle swarm optimization(PSO) algorithm. This model solves existing the learning and traditional neural network to speed of neural network is slow，and its easy to converge to local optimum. The application shows that this method is effective for reflect the stress deformation of nonlinear problems during establishment of neural network forecast model. This model significantly promotes the speed and precision of the calculation and provides the real time on line assessment of dam safety with a useful technical support.

Select

FUZZY COMPREHENSIVE EVALUATION ON STABILITY OF CO2 STORAGE IN DEEP NON-MINING COAL SEAM

WANG Yi，YANG Weifeng，ZHANG Xuguang，ZHAO Guorong，JI Yubing

2012, 31 (S1): 2932-2939

[PDF] 714 KB (10)

+

Show Abstract

To realize the muilt-factors quantitative evaluation on the stability of CO2 storage in deep non-mining coal seam，a fuzzy comprehensive evaluation method based on secondary evaluation model for evaluating the stability of CO2 storage in deep non-mining coal seam is proposed on the basis of the theory of fuzzy mathematics. Based on the principle of scientificity，rationality，operability and representativeness，eight primary factors and four secondary factors are established. A comprehensive evaluation system is constructed，where factors are quantitative graded according to four stability grades using fuzzy statistical method and experts grading method， to analyze the conformation of membership function of every factor. The analytic hierarchy process is used to distribute rational weight for every factor. Evaluation for engineering is conducted with geological exploration data of CO2-ECBM project in Qinshui basin in Shanxi province，achieving a satisfying evaluation result consistent with engineering reality. Fuzzy comprehensive evaluation method proves to be rational and operable for evaluating the stability of CO2 storage in deep non-mining coal seam，which provides theoretical support for choosing places to store CO2.

Select

PERMEABILITY EXPERIMENTAL STUDY OF GRITSTONE IN DEFORMATION AND FAILURE PROCESSES

WANG Xiaojiang1，2，RONG Guan1，2，ZHOU Chuangbing1

2012, 31 (S1): 2940-2947

[PDF] 2678 KB (15)

+

Show Abstract

Permeability experiments of deformation and failure processes of gritstone are carried out in triaxial test instrument. The permeability of gritstone in deformation and failure processes is analyzed. The impact of confining pressure on permeability of gritstone is studied. And the relationship between permeability and volume strain was discussed. It is shown that in the triaxial compression test，the total change law of permeability presents the corresponding stage characteristic of the curve of stress-strain. It is that the permeability reduces slightly with the increase of partial stress in the stages of micro fracture compression and elastic deformation；in the elasto-plastic stage，along with the expansion of new fractures，the permeability increases slowly at first and then sharply reaches the maximum value after peak point；at residual flowage stage，the fracture which controls the permeability of gritstone is compressed because the confining pressure and the permeability decreases. During the process of deformation and failure，the permeability decreases because the generation connected fissures is compressed by the confining pressure. The permeability is more sensitive to the change of hoop strain in the deformation and failure processes of rock sample. The greater the confining pressure is，the smaller the peak value and the post-peak residual value of permeability various curve of gritstone are，and the more gentle the curve of permeability-strain is. Lastly，based on the mass conservation equation of the theory of porous media，the relationship between porosity and volume strain is deduced. By using the Kozeny-Carman equation，the relationship between the permeability and volume strain is studied，the results show that the Kozeny-Carman equation has good applicability when pores dominate the flow channel.

Select

STUDY OF NONLINEAR DAMPING HYSTERESIS RESPONSE CHARACTER FOR ROCK SAMPLE

TANG Jie，SUN Chengyu，ZHOU Jiahui，GUO Yuan

2012, 31 (S1): 2948-2955

[PDF] 2687 KB (10)

+

Show Abstract

The multiple and multi-level cyclic loading tests for using the reservoir rock samples are carried out；and combining with theory analysis，the nonlinear damping hysteresis characteristics are studied. Experimental results show that：(1) At the unloading stage，the strain phase lags the stress phase；and at the loading stage，the strain phase response may lag，be equal to or be ahead of the stress phase. (2) Under multi-stage cyclic loading， exterior loop two-way elastic modulus，interior one-way elastic modulus and dynamic modulus of stress-strain curves are different. (3) Under different stress conditions，the waveform especially the coda waveform changes，that provides base for testing the wave velocity by code wave interference. (4) Small cycles in big cyclic have good consistency at the same stress level. As the existence of the sticky damping effect， the stress conversion point of small cycles can not be well memorized. The relaxation mechanism，the sticky damping mechanism and the plastic deformation mechanism are studied through theoretical analysis. All of them are phenomenological models，and can be used to describe the complex stress-strain properties of rock samples. Theoretical results can give good results qualitatively and quantitatively，comparing with experimental observations results. The study of nonlinear damping hysteresis characteristics under quasi-static cyclic loading is very useful.

Select

COMPLEX MEASUREMENTS OF GEO-STRESS IN DEEP DIVERSION TUNNEL AND RESEARCH ON DISTRIBUTION LAW OF REGIONAL STRESS FIELD IN QINLING MOUNTAIN

ZHOU Chunhua，YIN Jianmin，DING Xiuli，AI Kai

2012, 31 (S1): 2956-2964

[PDF] 976 KB (10)

+

Show Abstract

The there-dimensional(3D) and normal hydro-fracturing tests are firstly applied to study the geo-stress field in deep depth of near 1 000 m diversion tunnel in Qinling mountain，and the results obtained from the two methods are analyzed comparatively. The results show that the magnitude of maximum horizontal principal stress from the two methods is accordant and the value is 20–31 MPa；and the orientation is mainly in NW to NWW direction. The results verify the reliability of the geo-stress test result of 3D hydro-fracturing method. Specially，the orientation of maximum horizontal principal stress is nearly in EW direction in rockmass of deep tunnel，which is consistent with the distribution of region ancient residual tectonic stress，and further shows that the distribution of regional stress in Qinling mountain is complex. Based on the measurement results and mechanical parameters of surrounding rock around tunnel，many problems about the stress such as redistribution range of stress after excavation stress level of measured region，etc.，are all analyzed and evaluated. At last，the distribution law of geo-stress in Qinling area is generalized and the geo-stress measurement results are specially summarized in map，all of which can supply the theoretical and practical values for the detailed understanding of Qinling region evolution law and the design and construction of projects through the mountains.

Select

REASONABLE MALPOSITION SETTING IN CLOSE DISTANCE COAL SEAMS UNDER INFLUENCE OF INTERLAMINAR STRESSES

YANG Wei1，2，LIU Changyou1，2，YANG Yu1

2012, 31 (S1): 2965-2972

[PDF] 1594 KB (10)

+

Show Abstract

Considering the influence of stress distribution factor between layers，the combining research methods of the traditional rock pressure，elastic plane body theory and field measurement are adopted to analyze the issue of the coal face reasonable malposition setting under the condition of the combined mining face in close distance coal seam. The conclusions are obtained as follows：(1) The face malposition setting distance should satisfy the basic conditions calculated by the theory of the rock pressure. (2) Based on the influence scope of the lower coal seam abutment pressure got from the mechanical theory or the measurement analysis，the interlaminar stress influence scope is calculated by the theoretical method of semi-plane and get the correction value of the face malposition. (3) Comparing the face malposition correction value with the calculated result by the traditional rock pressure，the larger of the two face malposition value，and also satisfying the basic conditions calculated by the theory of rock pressure，is took as the reasonable malposition setting distance. Through the analysis of reasonable malposition setting in the context of actual production in Shigejie coal mine，the reasonable face malposition of 55 m is setted finally. In this condition，the safe and efficient production is guaranteed.

Select

EXPERIMENTAL STUDY OF CONSTITUTIVE RELATION FOR ROCK FRACTURE UNDER NORMAL CYCLIC LOADING

GUO Baohua，LI Xiaojun，SU Chengdong

2012, 31 (S1): 2973-2980

[PDF] 2312 KB (10)

+

Show Abstract

The normal deformation of rock fracture has important influence on its seepage and stress wave propagation feature. A constitutive model for rock fracture under normal cyclic loading is studied on basis of analyzing normal deformation mechanism of rock fracture，cyclic hysteresis and shape characteristics of test curves. 15 circles of normal closure-stress curves of coarse-grain and fine-grain marble sample fractures are got through laboratory tests. The first cyclic loading curve，whose fitting curve should be generated alone，is significantly different from other loading or unloading curves. A hyperbolic-power function with 4 parameters is chose to fit each loading and unloading curve after translating every curve to let its low-stress endpoint locate at original point. Both the accumulative total loading closure and residual unloading closure have good exponential function relations with cyclic numbers，which can be used to determine two endpoints of each fitting curve. The expression of relationship between the power function index and cyclic numbers is got by first fitting；and then，the expression of the power function coefficient is obtained by assumption of every fitting curve going through two endpoints of its corresponding fitting curve. Finally，the relationships of maximum aperture，initial stiffness and cyclic numbers are identified by next 2 times of orderly fitting. Hence the continuous fitting loading and unloading curves，which has higher fitting precision，can be determined by substituting the fitting values of three parameters into hyperbolic-power function expression；and then translating each curve to let its endpoints locate at the corresponding fitting points. The research has some practical values for numerical simulation of normal stress-closure curve of rock fractures under cyclic loading.

Select

DISCUSSION ON RELATIONSHIP BETWEEN POST-PEAK CURVES AND SHEAR STRENGTH PARAMETERS OF ROCKS SUBJECTED TO DIRECT SHEAR TESTS

ZHANG Guimin1，LI Yinping1，YANG Chunhe1，WANG Lijuan2，YANG Changlai3

2012, 31 (S1): 2981-2988

[PDF] 1452 KB (16)

+

Show Abstract

With the direct shear tests on groups of mudstone，dolomite and limestone specimens，the internal friction angleΦand cohesion c are obtained by using peak stresses under various normal stresses. Moreover，further analysis for curve of the shear stress-shear displacement shows that the post-peak curve is interrelated to the shear strength parameters. The value of shear stress drop between peak and residual shear stress is approximately equal to the value of the cohesion c；and the relationship between residual shear stress and normal stress can be described approximately by internal friction angleΦ. By comparison of the parameters obtained respectively from above two methods，the results indicate that when normal stresses satisfy certain selected conditions，the shear strength parameters calculated from post-peak curves can be seen as approximate value of the rock shear strength parameters. Based on theoretical analysis of above mentioned phenomena，an approximate method to calculate shear strength parameters is proposed by using post-peak curves of rocks subjected to direct shear tests；and its concrete calculating process is also presented. Additionally，this method also explains visually the physical meaning of post-peak curves of rocks.

Select

DISCUSSION ON DISTRIBUTION OF DYNAMIC STRESS AND GAS DRAINING EFFICIENCY IN COAL SEAMS BY BLASTING THROUGH LAYERS OF COAL-ROCK

GONG Min1，XIONG Benliang2，WANG Chuhan1，WANG Hua1

2012, 31 (S1): 2989-2996

[PDF] 2559 KB (10)

+

Show Abstract

The deep-hole blasting through strata has important role for outburst prevention in rock cross-cut coal uncovering and some special area. The difficulty of the research is caused by the area blasted in layers of coal-rock media and different burden in fan-patterned holes. Based on lots of mine experiments，a representative blasting theory through layers of coal-rock is studied by three-dimensional numerical simulation method. The numerical calculation models for the blasting through strata are constructed. The effective stresses variations of different locations at different times are acquired；the law that the effective stresses of different draining holes decreases with increase of the distance is analyzed；and distribution of effective stress along axis in the holes is discussed in the coal seams. The calculation results show that：(1) The perforation range of blasting cracks at top and bottom of the draining hole in layers of coal-rock media is up to 1.4 and 1.8 m respectively. (2) The average value of effective stress in bottom of the hole is 73% higher than in top at the same location because of actions of the stress interference and reflection in bottom of the hole. (3) The blasting effect in coal seam in layers of coal-rock media is better than in single coal seam. Under the same condition，the maximum value of the effective stress at top and bottom of the draining hole in the multi-media is 17%–42% and 6%–24% higher than in single coal seam. When average values of effective stress increases from 7.12 MPa to 12 MPa along axis of the hole，the gas draining gross increases more than 3 times.

Select

MICROSCOPIC MODELING AND MECHANICAL PROPERTIES OF OUTWASH DEPOSITS BASED ON OTSU STATISTIC OF IMAGE GRAY

SHI Chong 1，2，WANG Shengnian 1，2，LIU Lin1，2，XU Anquan1，2

2012, 31 (S1): 2997-3005

[PDF] 1795 KB (10)

+

Show Abstract

Based on digital image processing technology，a new method which can generate particle flow model from digital image is proposed to simulate mechanical behavior of outwash deposits. First of all，it implements preprocessing of digital image according to denoising method of images based on their decomposed bit planes. And then，Otsu is used to gain the adaptive threshold to accomplish the binarization of image so that soil and rock can be divided. Finally，it is the two dimensional particle flow code(PFC2D) compartment dislocation model of the real microstructure that can be built up by the proximate pixel interpolation algorithm. As an example，a outwash deposit case located at the front of Gushui hydropower station in Yunnan province is used，and the numerical simulation of biaxial compression tests are applied according to above-mentioned method. The results show that this new method overcomes the shortcomings of the axial compression compared with that builds up directly according to the position of pixel. The relationship between the stress and strain of outwash deposits has a feature of hardening under biaxial compression，and it also enhances the elastic modulus and peak strength because of the existing of rock mass. The increasing of bonding strength between soil particles has a greater impact on peak strength of the outwash deposits，while it isn′t obvious on initial elastic modulus. The outwash deposits meet Mohr-Coulomb strength theory approximately under low stresses. The angle of friction increases from 0°to 90°and the bonding strength also increases about 300 kPa compared with soil material excluding the impact of rock mass. Anyway，this method provides the basis of theory for the field outwash deposits in determination of parameters.

Select

STUDY METHODS FOR CREEP DAMAGE IN THEORETICAL RHEOLOGICAL MODELS AND SOME PROBLEMS

JIN Lei1，2，XIA Caichu1，2

2012, 31 (S1): 3006-3014

[PDF] 646 KB (14)

+

Show Abstract

In order to take into consideration of damage in theoretical rheological models(TRM)，current approach，based on Lemaitre equivalent strain theory，is to obtain creep damage equation through the replacement of the Caucy stress with effective stress in creep equation of the TRM with constant rheological parameters，thus the time-dependent damage can be introduced. Such an approach is equivalent to the substitution of the rheological parameters p with p(1－D) in creep equations of TRM. With the parameters being time-dependent，a problem similar to that in nonlinear TRM，the failure to produce correct creep equation of nonlinear TRM via direct replacement of time-dependent rheological parameters in creep equations of linear TRM with functions，will arise. Based on the hypothesis that damage and creep are simultaneous，this paper proposed an alternative way to obtain creep damage equation：to deduct it from the revised constitutive law in which the Caucy stress is replaced by effective stress. Further，another way to obtain creep damage equation，that is through principle of superposition，is given，and its correctness is proven. On the basis of the second way，the method to obtain creep damage equation when damage is not in concurrence with creep is proposed. In addition，problems in some current studies are discussed and more valid answers are suggested.

Select

EXPERIMENT AND MODEL STUDY OF RHEOLOGICAL CHARACTERISTICS FOR DEEP AMPHIBOLITE

CAO Ping1，ZHENG Xinping1，LI Na1，ZHANG Xiangyang1，2

2012, 31 (S1): 3015-3021

[PDF] 1638 KB (14)

+

Show Abstract

Relaxation experiment on deep amphibolite samples from Jinchuan II mining area as conducted using multi-step incremental loading method. Further analysis of relaxation experimental results was made in contrast to those of creep experiment conducted by multi-step incremental cyclic loading and unloading. Creep experiment mainly reflected the long-term strength of rocks；while relaxation test proved that the rocks had residual strength after rupture. Continuous relaxation law and non-continuous ladder-type relaxation law were found through relaxation curves. The result showed that the non-continuous ladder-type relaxation law was closely related to micro-cracks initiation and original cracks propagation. The elastic and viscoelasto plastic model(K-B model) was adopted to research the visco-elasticplasticity of deep amphibolite based on the test data. The analysis of fitting curves and fitting parameters illustrated that the curves of K-B model were well agreed with those of both creep and relaxation rock samples. It was concluded that the K-B model can properly describe the rheological characteristics of amphibolite in Jinchuan II mining area.

Select

IMPLEMENTATION OF SAEB-AMADEI MODEL INTO USER-DEFINED JOINT CONSTITUTIVE MODEL IN UDEC

WU Yuexiu1，2，LIU Quansheng1，2，LU Haifeng1，LI Jinlan1

2012, 31 (S1): 3022-3030

[PDF] 2696 KB (12)

+

Show Abstract

The mechanical behavior of fracture under the condition of constant normal load(CNL) is different from that of constant normal stiffness(CNS). The effect of joint normal deformation on joint shear deformation and joint dilation is considered in the Saeb-Amadei joint constitutive model，as well as the influence of joint match. And the Saeb-Amadei joint model is suitable for CNS and CNL condition. Thus，the Saeb-Amadei joint is adopted to study the HM coupling behavior of fractured rock mass. Through the User-defined joint constitutive models of UDEC，the implementation program named Userjsa is compiled with C++ language. Then，the numerical uniaxial compression test and direct shear test are simulated. By comparing the numerical results with the analytical results，the implementation program is verified. It is proved that the implementation joint model can be used to study the HM coupling behavior of fractured rock mass.

Select

STUDY OF PLASTIC MECHANICAL MODEL OF ROCK SALT WITH DISSOLVING EFFECT

TANG Yanchun1，2，ZHOU Hui1

2012, 31 (S1): 3031-3037

[PDF] 738 KB (10)

+

Show Abstract

Through analysis of mechanism of variation for rock salt mechanical properties with dissolving effect，rock salt plastic mechanical model with dissolving effect has been established. The analysis results show that mechanism of variation for rock salt mechanical properties with dissolving effect is because that macro- mechanical parameters of rock salt，such as cohesion，have been varied with dissolving effect；but rock salt failure mechanism has been unchanged essentially. With strain harding-softing model which can be used to reasonably describe rock salt mechanical behavior，rock salt plastic mechanical model without dissolving effect has been established；and associated with the conventional triaxial compression test results，the expressions between cohesion and internal friction angle without dissolving effect and equivalent plastic strain have been obtained. Based on mechanism of variation for rock salt mechanical properties with dissolving effect and rock salt plastic mechanical model without dissolving effect，and under the premise that with dissolving effect，the value of cohesion has been changed，the rock salt plastic mechanical model with dissolving effect has been established. At last，based on the uniaxial compression meso-mechanical test results of rock salt with coupled stress-dissolving effect，the variation rule of cohesion on dissolving phase with dissolving time is calculated by combined FLAC-Genetic Algorithms. The formula of cohesion on reloading phase after dissolving is obtained；and the variation rule of cohesion of rock salt plastic mechanical model with dissolving effect has also been obtained.

Select

ANALYSIS OF PEAK DILATION STRENGTH AND MODEL OF PEAK DILATION ANGLE FOR ARTIFICIAL JOINT

TANG Zhicheng1，2，XIA Caichu1，2，SONG Yinglong1，2，FU Pengfang2

2012, 31 (S1): 3038-3044

[PDF] 950 KB (11)

+

Show Abstract

Several shear tests have been conducted on different artificial joint samples at 5-level normal stress to study the relationships between peak shear dilation angle，peak shear strength and normal stress，joint roughness. These samples have the same morphology. The experimental results are analyzed by commonly used dilation models，which are Barton peak dilation model，Schneider peak dilation model and Jing peak dilation model. The analysis results show that there are some difference between the observed value and predicted value by these models. Usually，the predicted value under low normal stress for Schneider model and Jing model is too small，but that under high normal stress is too large. The results also show that there is a large difference between observed value and results calculated by Barton dilation model. After analyzing the boundary condition of existence of shear dilation angle，a new hyperbolic peak dilation model is put forward，using as model parameter. A new peak shear strength criterion is proposed based on this new peak dilation model. The experimental data are compared with peak strengths calculated by this new peak shear strength criterion，the above three strength criteria and GG strength criterion. There is a good agreement between new strength criterion and observed data.

Select

CONSTITUTIVE MODEL FOR GAS HYDRATE-BEARING SEDIMENTS CONSIDERING DAMAGE

WU Erlin，WEI Houzhen，YAN Rongtao，WEI Changfu

2012, 31 (S1): 3045-3050

[PDF] 573 KB (15)

+

Show Abstract

When a gas hydrate-bearing sediment is loaded，inter-particle processes such as dislocating，slipping and rolling will take place. Under small loading condition，the sediment deforms elastically；with the applied load increasing，plastic flow may occur，resulting in re-arrangements of hydrate crystal and the sediment deforms plastically；as the applied load further increasing，failure of the sediment will appear. This process represents the whole process of the damage producing and developing in the sediment. From the mesomechanics mechanism perspective of composite material，the material characteristics of gas hydrate-bearing sediments is investigated；and the relationship between hydrate saturation and equivalent elastic constants is established. Based on the principles of damage mechanics，the expression of damage variable is identified；and then a constitutive model for gas hydrate-bearing sediment considering damage is developed. The calculation results are compared with the experimental data for a gas hydrate-bearing sediment with different hydrate saturations. It is shown that the presented model can describe the stress-strain behavior of gas hydrate-bearing sediments quite well and the reasonability and feasibility of the model are verified.

Select

A NEW MECHANICAL MODEL FOR ACCUMULATIVE DAMAGE OF ROCK MASS BASED ON SYNERGETIC ANALYSIS

YU Guangming1，PAN Yongzhan1，2，CAO Shanzhong3，WU Yanxia1，KANG Yin1

2012, 31 (S1): 3051-3054

[PDF] 582 KB (10)

+

Show Abstract

Rock mass is treated as a system composed of rock and discontinuities based on the its characteristics of discontinuous. The order parameter equation of rock block was gained by means of synergetic microtreatment method，where the order parameter is displacement of rock blocks，which is divided by structural plane，relative to its original balance position. A new mechanical model for accumulative damage of rock mass is put forward through the solution of this equation. Comparison between the calculation results and other research results shows that this new mechanical model can explain many phenomena of rock mass under dynamic loads such as bearing capacity and damage accumulative effect more rationally.

Select

STUDY OF FLUID-SOLID COUPLING MODEL CONSIDERING CONVECTIVE DIFFUSION OF CO2 MISCIBLE FLOODING IN LOW PERMEABILITY RESERVOIR

LI Nan，CHENG Linsong

2012, 31 (S1): 3055-3060

[PDF] 703 KB (25)

+

Show Abstract

In order to study the influence of convective diffusion and fluid-solid coupling on CO2 miscible flooding in the low permeability reservoirs，the coupling control equations of three fields which are multi-phase and multi-component seepage field，convective diffusion field and strain field are deduced；then the solution method is given. This model considers emphatically the impact of convective diffusion，miscible phases and stress and strain of rock skeleton on the whole flow process and constrains the boundary conditions. The example analysis is carried out by applying the fluid-solid coupling equations which are established by considering convective diffusion. The study results show that the established model comprehensively considers the influence of convective diffusion and fluid-solid coupling on seepage flow，which reflects the availabilities of the model and calculation method. The model improves the simulation precision of CO2 miscible flooding. The calculation results of this model and the conventional numerical simulation results are found to have certain comparability. Meanwhile，based on the calculation results，the influence of convective diffusion on CO2 miscible flooding is described quantitatively in the model in terms of interfacial tension，productivity，miscible area and so on.

Select

CREEP ACOUSTIC EMISSION RULE OF GRAY GRANITE FROM SHANDONG PROVINCE WITH THERMO-MECHANICAL COUPLING EFFECTS

WU Jinwen1，ZHAO Yangsheng1，WAN Zhijun2，FENG Zijun1，DONG Fuke3，LI Yi4

2012, 31 (S1): 3061-3067

[PDF] 1182 KB (13)

+

Show Abstract

The creep acoustic emission rule of granite(200 mm×400 mm) was tested under three different temperatures，axial pressures and confining pressures. The research results are as follows：(1) Under the condition of 300 ℃，axial pressure of 94 MPa and confining pressure of 75 MPa，the creep process of granite experiences transient and steady creep states. The acoustic emission in transient creep state is stronger than that in steady creep state. The acoustic emission frequentness is more steady and the intensity decreases in steady creep state. Under the condition of 400 ℃，axial pressure of 125 MPa and confining pressure of 100 MPa，the creep process of granite only experiences steady creep state and the acoustic emission is similar with steady creep state in 300 ℃. Under the condition of 500 ℃，axial pressure of 175 MPa and confining pressure of 125 MPa，the acoustic emission signal is so weak that the acoustic emission rule in creep process cant be explained. (2) In the creep test with high temperature and high pressure，the acoustic emission signal becomes weak due to partial plastic deformation and partial plastic damage inside granite with the temperature increasing.

Select

JOINT CLOSURE DEFORMATION MODEL BASED ON ASPERITY-SUBSTRATE DEFORMATION

TANG Zhicheng1，2，XIA Caichu1，2，SONG Yinglong1，2，FU Pengfang2

2012, 31 (S1): 3068-3074

[PDF] 713 KB (21)

+

Show Abstract

Joint surface topography has important effect on its closure deformation behavior. For a given joint，the contact state is also a key factor and different contact states will get curves with big difference in joint closure test. Greenwood model based on Hertz theory is a commonly used model but it is difficult to consider the contact state of joint surface. An improved version of original Greenwood model was addressed and this model introduce composite topography，whose height at any point is the sum of the height of the upper and lower joint surfaces measured form arbitrary reference planes. Elasticity analysis showed that the asperity contacts can cause compression of the asperities and the deformation of the substrate. Greenwood model and the Brown model do not consider the asperity and substrate deformation. A single asperity mechanical model extended to the whole rough surface based on statistical theory. Then，a new improved version of Brown model with inclusion of compression of the asperities and the deformation of the substrate is formulated. At last，comparison between this improved Brown model and original Brown model is conducted to analyze joint closure deformation data from different contact states of joint with the same topography；and the rationality of the improved Brown model is verified.

Select

MODEL TEST STUDY OF ANCHORING AND REINFORCING MECHANISM OF PRESSURE DIFFUSION ANCHOR CABLE

LIU Hong，ZHOU Depei，WANG Zhibin

2012, 31 (S1): 3075-3081

[PDF] 488 KB (15)

+

Show Abstract

A new test device and a new test method are adopted to implement grading cyclic loading onto each anchor unit and study the anchoring and reinforcing mechanism of pressure diffusion anchor cable by geological mechanics model test. The test results show that：as far as the pressure diffusion anchor cable with two anchor units is concerned，the strain and axial force of the grouting body of the first unit are influenced by the distance between the bearings and attenuates faster than that of another unit，the mode of the strain distribution and the average bond stress distribution of the units are smaller in the front unit and bigger in the back unit after loading. For the pressure diffusion anchor cable with three anchor units，compared with the previous loading，the peak strain and axial force of the first unit fall with different levels after loading 0.6 kN onto the 2nd and 3rd units；and the average bond stresses of the loaded unit and unloaded unit are improved. For the pressure diffusion anchor cable with four anchor units，the peak strain and axial force and average bond stress of loading unit or unloaded unit have been improved，while the peak strain axial force and average bond stress of the loaded units reduce after grading cyclic loading. Under conditions of certain anchor length，the number of the bearing body has a considerable influence on the effective transfer of loads，especially the bond stress transfers in different ways. The experimental results have a good reference value for the correct analysis of anchoring and reinforcing mechanism and engineering design of the pressure diffusion anchor cable.

Select

RESEARCH ON CONSTRUCTION METHOD OF STOCHASTIC JOINTS 3D-NETWORK MODEL OF EQUIVALENT ROCK MASS

WU Shunchuan1，ZHOU Yu1，2，GAO Yongtao1，MISRA A2

2012, 31 (S1): 3082-3090

[PDF] 1990 KB (15)

+

Show Abstract

Because that it is hardly applicable for mechanical analysis of rock mass currently，equivalent rock mass model，which is constructed to reflect actual space status of joints，is the research foundation for stability analysis of rock mass engineering. Taking Baiyunebo eastern iron open pit in Inner Mongolia as research background，based on the field joint investigation by scanline，the dip direction，dip angle，spacing and trace length of field joints are statistically analyzed with bias correction；and then their corresponding probability distribution models are established by using probability statistics theory. Based on these work，Monte Carlo stochastic simulation theory and Matlab software are adopted to obtain simulated joints data. Based on OPEN GL technique，these data are then used to construct visual stochastic joints 3D-network model of equivalent rock mass，which reflects the distribution feature of field joints. The simulation result shows excellent statistical similarity with the measured data. These research achievements can be utilized by equivalent rock mass technique，and can lay a foundation for following quantitative research of rock mass property，such as deformation，strength，size effect，anisotropy，representative elemental volume(REV)，key block identification，excavation effect and fracture mechanism.

Select

DYNAMIC MODEL AND NUMERICAL SIMULATION FOR HARD ROCK NEAR EXPLOSION CAVITY

CHEN Wanxiang1，WANG Mingyang2，QIAN Yuehong2，FANG Yingguang1，WU Hao2

2012, 31 (S1): 3091-3097

[PDF] 807 KB (22)

+

Show Abstract

The modified C. C. Grigorian model was introduced to investigate the dynamic deformations of hard rock near explosion cavity after wavefront，the equations under high pressure and the incremental constitutive equations were presented. The dynamic responses of coupled-charge rock near explosion cavity under high confining pressure were calculated by introducing user-defined subroutine based on the LS-DYNA9703D secondary development platform，and the calculation results were compared with other results of experiment，elastic model or PSEUDO_TENSOR model. The results indicated that the calculation results of modified C. C. Grigorian model were in good agreement with the results derived from the similar experiment；and the modified C. C. Grigorian model was reasonable to investigate the dynamic deformation and fracture of hard rock near explosion cavity under high confining pressure after wavefront. Due to the softening effects of cracked rock，the permanent displacements of explosion cavity that calculated by using modified C. C. Grigorian model were obvious different from those based on elastic model and PSEUDO_TENSOR model，and the velocity attenuation of surface medium of explosion cavity after wavefront was in good agreement with those of experiment. The permanent displacements after expansion of explosion cavity were greatly affected by the values of confining pressure，and the higher the confining pressure was，the lower the permanent displacement was. The permanent displacements after expansion of explosion cavity were sensitive to the relaxation characteristic time.

Select

STRESS CALCULATION AND RELIABILITY ANALYSIS OF ARCH DAMS CONSTRUCTED ON ROCK FOUNDATION WITH WEAK ZONE

WU Qingxi1，LU Jun2，YANG Mingzhu1

2012, 31 (S1): 3098-3103

[PDF] 952 KB (17)

+

Show Abstract

The main difficulty of reliability analysis of arch dams is due to the rock materials are not continuous，inhomogeneity and its elastoplasticity of the constitutive relations and the huge computation workload. To solve the difficulty above，based on elastoplastic constitutive model，the main region and key problems of structural reliability analysis are determined by structural analysis of the arch dam. Then the reliability index of the region of arch dam and its variation rule are obtained by the technique of response surface method. Based on the structural computation analysis of a arch dam，reliability indices of the basement and weak formation of the arch dam are calculated and the variation rule of reliability index is sketched. The calculated results confirmed the correctness and practicality of the procedure solving the reliability analysis of arch dams.

Select

NONLINEAR FINITE ELEMENT ANALYSIS OF MECHANICAL PROPERTIES OF INFLATABLE ANCHORS

PENG Wenxiang，XU Songshan，CAO Jiawen，YIN Quan

2012, 31 (S1): 3104-3109

[PDF] 977 KB (8)

+

Show Abstract

Nonlinear finite element analysis method is used to carry out the numerical analysis of indoor model test of inflatable anchor. Based on the conditions of the inflation pressure(100 kPa)，buried depth(20 cm) of the anchor，the density of sand body(1 500 kg/m3)，and length(20 cm) and thickness(2 mm) of the rubber，mechanical properties of inflatable anchor are discussed. The displacement at the top of the inflatable anchors is recorded at different ranks of pulling forces，then the load-displacement curve is drawn，at last，a series of nephograms of displacement and strain have been obtained. The changes of displacement and strain of the inflatable anchor and sand body when the pull force increases are reflected directly and clearly by these charts；then the critical states of inflatable anchors losing effectiveness can be seen. Stress form and stress distribution of sand have been confirmed under three different kinds of states. Furthermore，the sand body failure mode is got when inflatable anchor lost its efficacy. Through comparing the load-displacement curves obtained by numerical simulation and indoor model test，it is shown that the comparison results are basically the same；so the numerical result is reliable.

Select

NUMERICAL SIMULATION OF SIZE EFFECT IN PIPING EROSION MODEL TEST FOR DOUBLE-STRATUM DIKE FOUNDATIONS

LIU Changjun，DING Liuqian，SUN Dongya，YAO Qiuling

2012, 31 (S1): 3110-3116

[PDF] 811 KB (14)

+

Show Abstract

Mathematical model and simulation methodology for dynamic development process of piping erosion in double-stratum dike foundations are established. Moreover，laws and mechanism of size effect in piping erosion model tests for double-stratum dike foundations are studied by numerical simulation；and correction methodology for small scale piping erosion model tests in double-stratum dike foundations is also presented. Numerical results show that：(1) Using the generalized mathematical model，size effect in piping erosion model tests for double-stratum dike foundations and dynamic development process of piping erosion are well simulated and numerical results fit the model test ones very well. What is more，seepage field distribution inside sand specimen and data hard to observe in model tests are obtained. (2) Model test sizes have a great influence on the critical hydraulic head and dynamic development process. Critical hydraulic head decreases with gradually smaller amplitudes as the width and depth of the model increase. (3) By theoretical analysis and numerical simulation，the available model test results are influenced greatly by model size. The model is improved with width and depth increase to 1.7 times and 0.85 times of dike body length separately，while the distance from exit of piping to upstream surface is 1.4 m. The influence radius of piping failure zone after being modified is about 0.85 times of dike body length.

Select

RESEARCH ON APPLICATION OF COUPLING TECHNIQUE OF ADAPTIVE CONTINUUM/DISCONTINUUM PERIODIC BOUNDARY CELL TO EQUIVALENT ROCK MASS

WU Shunchuan1，ZHOU Yu1，2，GAO Yongtao1，MISRA A2

2012, 31 (S1): 3117-3122

[PDF] 1055 KB (11)

+

Show Abstract

The coupling technique of adaptive continuum/discontinuum(AC/DC) periodic boundary cell，as a new construction method of calculation model in PFC based on particle flow theory，was introduced. In this method，a compacted and balanced pbrick was constructed；and then it was replicated mirrorlikely to construct particles model. Therefore，with decreasing computing time and saving computing resource greatly，it can avoid the defect of consuming great time in the generation of model to reach the mechanical equilibrium state. Taking an uniaxial compression test of equivalent rock mass for example，under the same initial calculation condition，the results produced by AC/DC technique and general method were compared in uniaxial compressive strength，stress-strain curves and failure characteristics，displayed highly similarity. The research results show that the computational efficiency of AC/DC technique is much higher than that of general particles construction method，and the advantage will be particularly prominent with the increment of model size. So its implementation of AC/DC technique can lay a solid foundation for following scientific research of engineering-scale rock mass property.

Select

SIMULATIONS OF CRACK PROPAGATION IN ROCK-LIKE MATERIALS USING PARTICLE FLOW CODE

YANG Qing1，2，LIU Yuanjun1

2012, 31 (S1): 3123-3129

[PDF] 1008 KB (8)

+

Show Abstract

By using a particle flow code—PFC2D，numerical simulations on samples containing two parallel cracks with different rock bridge angles under uniaxial compression are conducted to research the cracks propagation and coalescence. The cracks propagation process and the number of microcracks have been tracked by functions in PFC. Numerical results show that：with the increasing of rock bridge angle under uniaxial compression，the crack coalescence patterns gradually evolve from tensile mode(≤68°) to tensile-shear mixed mode( = 90° and 113°) and shear mode( = 135°)；and the samples peak strengths gradually decrease. The macroscopic secondary shear zone mainly comprise of tensile microcracks and bits of shear microcracks. Comparison between the numerical simulation results with the experiment results indicates that PFC can simulate the crack coalescence process properly.

Select

NUMERICAL EXPERIMENT OF ACCELERATION RESPONSE IN FREE LIQUEFACTION FIELD

HE Jianping1，CHEN Weizhong2

2012, 31 (S1): 3130-3137

[PDF] 1347 KB (12)

+

Show Abstract

Soil liquefaction would make ground failure and have effect on ground acceleration in addition. The liquefaction numerical simulation experiment of free field by the Finn model is realized；and the acceleration response question of liquefaction field has been studied. The study results indicate that：the liquefaction field acceleration response amplitude has relations with input acceleration amplitude，the acceleration magnification factor in liquefaction field decreases along with the increasing input seismic amplitude. The acceleration response essential feature of liquefaction field is low-frequency amplification，high-frequency reduction，the low-frequency amplification effect is higher than the high frequency reduction effect obviously. The dry sand elastic field also has the low-frequency amplification and high-frequency filter effect，but the effect of liquefaction field is more remarkable than that of elastic field. Regarding the low frequency excitation，if the liquefaction field acceleration enlarges，and the field have liquefied，then the field acceleration weakens. If the liquefaction field acceleration enlarged，but the field had still not liquefied，then the field acceleration maintained the stable forced oscillation condition. The elastic field acceleration response increased gradually from field bottom to top，the acceleration magnification in field surface is most remarkable，the acceleration magnification of liquefaction field is most remarkable in the field middle spot. The acceleration response frequency characteristic is not bright with high amplitude input，the liquefaction field acceleration response frequency characteristic is quite obvious with the low acceleration amplitude and low frequency input. If the acceleration magnification factor in conventional elastic field is used to anti-seismic design of underground structure，it will lead the underground structure to be unstable. Research results will provide a theoretical and experimental basis for the dynamic analysis of underground structures passing through liquefied soil layer.

Select

THEORETICAL ANALYTICAL SOLUTION OF STRESS DISTRIBUTION IN ELASTICITY STAGE OF SPHERICAL CAVITY STORAGE CAVERN IN SALT ROCK

WANG Wu1，2，XU Hongfa1，JIANG Miao1，FANG Qin1

2012, 31 (S1): 3138-3144

[PDF] 609 KB (8)

+

Show Abstract

Based on the assumption that the storage cavern is sphere，and using a basic principle that the stress could be superimposed in the elastic stage，the force modes of spherical gas storage cavern is disintegrated into hydrostatic pressure and vertical stress. Through the superposition of analytic results of surrounding rock stress distribution under the two kinds of force modes，the elastic stress distribution functions in surrounding rock of the spherical gas storage cavern in salt rock under remote field triaxial compressive stresses and internal pressure are derived. The numerical analysis of spherical gas storage cavern of salt rock is conducted under the same condition. Comparison shows that numerical simulation results are in good agreements with theoretical calculation results；and the presented analysis method is verified to be feasible. Then Hoek-Brown criterion is used to estimate the stability of spherical cavity storage cavern，and the limit of internal pressure is obtained when the plastic failure of gas storage cavern doesnt appear.

Select

DISCUSSION ON DAMAGE MODULUS FOR ROCK BASED ON MULTI-LEVEL LOAD TEST

LIU Jianfeng，PEI Jianliang，ZHANG Ru，WANG Lu

2012, 31 (S1): 3145-3151

[PDF] 664 KB (14)

+

Show Abstract

According to the propositional loading speed for axial compression test in Standards for Tests Method of Engineering Rock Masses(GP/T50266—1999) and the operational status of natural gas store cavern during gas injection and production fatigue cycles，the damage unloading modulus of salt rock being surrounding rock for natural gas store cavern were tested，and the marbles as the contrast stone are also tested. All of the tests are realized on MTS815 Flex Test GT rock mechanics test system. The test types include the uniaxial compressive loading and unloading test，and the uniaxial compressive test with low cyclic loading. The loading standard is controlled by axial load and during each test，the stress amplitudes have 7 grades for each specimen. The loading wave for low cyclic loading test is sine wave with the frequency of 1.0 Hz，and the cyclic number of every level cyclic stress is no less than 30 cycles. The research results show that salt rock has larger irreversible deformation at the turning position between reloading and unloading，corresponding elastic deformation response is slow；but the results for the marble are contrary，the shape of stress-strain hysteresis loops is ribbon for salt rock，while it is tine lobation for marble. The changing tendency of unloading modulus for salt rock is reverse by the two test methods above，while it is consistent with each other for marble，and the unloading modulus decreases with the increasing loading stress. The effect of loading stress amplitude on the increment of irreversible deformation for salt rock is more prominent than that of cyclic numbers. The research reveals the damage evolution characteristics for salt rock under the operational loading of store carven.

Select

CALCULATION FOR A TYPE OF RETAINING STRUCTURE WITH DOUBLE-ROW PILES

FAN Qiuyan1，XU Shengcai2，CUI Feng3

2012, 31 (S1): 3152-3158

[PDF] 610 KB (12)

+

Show Abstract

For the reason that the retaining space suffers from the restraint，a type of retaining structure with double-row piles is designed as the structure without soil solum between the pre-row pile and post-row pile，to form the soil-retaining spatial door-frame structure in the post-row pile. At present，there is no calculation method for internal force of such kind of retaining structure with double-row piles. For this type of double-row piles，the pre-row pile and the post-row pile are both considered as elastic foundation beam placing upright. The soil spring is employed to simulate the soil resistance under excavation surface. The sections of double-row pile are divided on the basis of differential equations of elastic foundation beam deflection to establish internal force equations of sections. The power series method is used to determine the internal force and deformation of the pile body below the excavation surface with the boundary condition of pile tip. Under the deformation compatibility condition of middle section of coupling beam，a equation of force method is established to get the internal force of middle section of coupling beam；and then the internal forces of different sections of the pre-row pile and the post-row pile are obtained. Finally，combining with the engineering examples，this type of retaining structure with double-row piles is calculated and the calculation results are compared with the measured statistics. Some valuable suggestions are put forward for design of this type of retaining structure with double-row piles.

Select

ISOLATION OF PLANE ELASTIC WAVES BY DISCONTINUOUS BARRIERS COMPOSED OF SEVERAL ROWS OF PILES

XU Ping

2012, 31 (S1): 3159-3166

[PDF] 636 KB (8)

+

Show Abstract

The lengths of piles are considered as much larger than their diameters，so the isolation of incident plane elastic waves(P waves，and S waves) by discontinuous barriers composed of several rows of piles can be simplified as a two-dimensional plane problem. The conformal mapping method of complex functions and expansion method of wave field potential functions are adopted，the stresses and displacements at the boundaries between the piles and their adjacent soils are considered as continuous，and then the theoretical solutions about the undetermined complex coefficients of scattering and infracting wave potential functions are obtained. By studying the normalized displacement amplitudes，which are the ratios of displacement amplitudes of soils behind the barriers caused by both the incident and scattering waves to those only by the incident waves，the isolation effects of the barriers composed of one，two and three rows of piles are compared，and the results reveal that：(1) When the barriers width and piles numbers of every row are the same，the isolation effect of P waves，SH waves and SV waves by the same barriers composed of several rows of piles all increase with the increasing rows number of piles. (2) When the barriers width and total piles number are the same，the isolation effect of P waves，SH waves and SV waves by one row of tight piles are better than that by two rows of staggered piles. (3) The isolation effects of SH waves and SV waves are better than those of P waves by the same barriers composed of several rows of piles.

Select

EXPERIMENTAL STUDY OF NEGATIVE SKIN FRICTION FOR MAN-MADE CAST-IN-SITU BELLED PILES IN LOESS SOIL FOUNDATION

CAO Weiping1，ZHAO Min2

2012, 31 (S1): 3167-3173

[PDF] 1572 KB (20)

+

Show Abstract

Field tests were conducted to investigate the behavior of negative skin friction，positive skin friction，pile end reaction and neutral plane depth for man-made cast-in-situ belled piles in loess under pre-immersing and loading condition. The test results were also compared with the regulations of the technical code for building pile foundation of China. The results show that：(1) With the pre-immersing，negative skin friction，positive skin friction and pile end reaction are induced and increase with further immersing and the neutral plane gradually descend. The neutral plane depth ratio reaches 0.54–0.61 at the end of pre-immersing process，which is far smaller than that introduced in the technical code for building pile foundation of China. (2) When vertical load is applied on the pile head，negative skin friction decrease accompanied by the increasing of positive skin friction and pile end reaction as well as the ascending of the neutral plane. The neutral plane depth ratio reaches about 0.15–0.61 when P = 11 000 kN，which is also far smaller than that introduced in the technical code for building pile foundation of China. (3) The measured negative skin friction and its distribution dramatically differ from the ones calculated according to the technical code for building pile foundation of China. (4) The negative skin friction and the neutral plane depth are in a dynamic process with the immersing and the loading as well as the pile shaft diameter.

Select

study of dynamic stress-strain relationship of loess under seismic loading

DENG Longsheng1，FAN Wen1，2，3

2012, 31 (S1): 3174-3180

[PDF] 1772 KB (18)

+

Show Abstract

The dynamic triaxial text was carried out on the loess sample taken from Xijiawan landslide of Xiajiadalu Village in Xiji County，South of Ningxia Province，to research its dynamic stress-strain relationship acted by seismic wave. Considering the different amplitudes，durations and excellent frequencies of seismic wave having great effect on the test result，so the relationship between intensity and acceleration attenuation of the field were studied using the method of regression and conversion analysis based on its macrograph intensity data，and then，the seismic risk analysis has been carried out and the earthquake wave of the field with the 10% exceedance probability in the following 50 years was gained. The results showed that the stress-strain relationship is complicated very much，and which could be predigested as a series of ellipse loop with different sizes，stations and shapes，and the shear module could be expressed the function of dynamic stress，strain and consolidation press，which could be changed as a power function. The dynamic stress-strain relationship of loess and the function have a good correlation by a large number of tests.

Select

STUDY OF MODEL MATERIAL AND SCALING LAWS DESIGN OF DYNAMIC CENTRIFUGE SHAKING TABLE TEST FOR A SOIL-STRUCTURE INTERACTION SYSTEM

LIU Jingbo，ZHAO Dongdong，WANG Wenhui

2012, 31 (S1): 3181-3187

[PDF] 742 KB (8)

+

Show Abstract

In order to obtain model material with low strength and low modulus which can be used to make dynamic centrifuge model to study damage phenomena in the dynamic centrifuge shaking table test，orthogonal experimental design method to investigate plaster performance with different mixing proportion are studied. Based on the experiment results，an appropriate plaster mixture is selected to make the model for centrifuge shaking table tests. Furthermore，the plaster is treated by waterproof measures and underwent waterproof test. The results show that the waterproof plaster buried in moist soil can maintain strength and modulus. Similitude design of a model test concerns the size and materials of the model in prophase of a test and also concerns the management of data after the test，so it is very important for shaking table tests. Similitude design of the dynamic soil-structure interaction test on shaking table system for geotechnical centrifuge is carried out by means of dimensional analysis method，which is based on theorem of Bockingham . The main aim of the similitude design in the system is to induce strong soil-structure interaction as in the prototype. So the similitude design should maintain similar relative stiffness and inertial force between soil and structure as in the prototype. Based on the required similitude，plaster model and micro-concrete model are designed，and the analysis about the two models is conducted.

Select

ANALYSIS OF SEISMIC ACTIVE EARTH PRESSURE OF COHESIVE SOIL BEHIND RETAINING WALL

XIA Tangdai1，2，KONG Xiangbing1，2，WANG Zhikai1，2，CHEN Weiyun1，2

2012, 31 (S1): 3188-3195

[PDF] 1411 KB (17)

+

Show Abstract

Based on the planar rupture surfaces hypothesis of Mononobe-Okabe theory，considering the effect of amplification of seismic accelerations and using the pseudo-dynamics method，the seismic active earth pressure coefficient，the resultant force of seismic active earth pressure and the distribution of active earth pressure on a rigid retaining wall supporting cohesive backfill are obtained respectively. Time and phase changes within the backfill are also considered. On this basis，the most unfavorable conditions are investigated by an optimization algorithm. Then the effects of horizontal and vertical seismic accelerations，internal fiction angle，wall friction angle，retaining wall angle and amplification on the inclination of the slip surface on active earth pressure coefficient，critical depth，the location of resultant force and the distribution of active earth pressure are discussed. The results show that the distribution of seismic active earth pressure is nonlinear. The existence of seismic acceleration induces a considerable increase in the active earth pressure of cohesive soil. The retaining wall angle and amplification effect of seismic accelerations have obvious influences on the critical depth，location of resultant force and distribution of passive earth pressure.

Select

APPLICABLE CONDITIONS OF DYNAMIC CONSOLIDATION METHOD IN SATURATED SOIL FOUNDATION

Jiang Rongfeng

2012, 31 (S1): 3196-3202

[PDF] 1482 KB (11)

+

Show Abstract

According to some typical field tests，the validity of soil properties and drainage condition for saturated soft soil foundation by dynamic consolidation method are studied. The treatment techniques of the method are discussed，which include the development and dissipation of pore water pressure，single point tamping energy，compacting number，the time between tamping and the next tamping，and the affecting scopes，etc. The result shows that the drainage conditions，for various saturated soils，are different from each other. In practical engineering，design parameters and the bearing capacity of reinforced grounds are determined by soil properties. In a certain depth of soil layer，the pore water pressure induced by impact loading is usually higher than its self-weight stress and then produces many fissure channels，which accelerates the drainage process. For the ground soil with low permeability，drainage measurement and small dynamic loading are should be adopted，but for the ground soil with higher permeability，a greater dynamic loading should be adopted.

Select

LAW STUDY OF SATURATED CLAY DISCHARGE WATER RESPONSE WITH PRESSURE

Zhang Bingfeng1，Zhao Jian1，Tao Yuezan2

2012, 31 (S1): 3203-3208

[PDF] 717 KB (16)

+

Show Abstract

Base on compaction test for saturated clay of different hydrophilic properties under different pressures，the relationships between hydrophilic property，film water and stress are researched. The results show that，with the external pressure increasing，the film water in soil discharges along with void ratio reduces when the void ratio reaches a critical value，and the volume of pore water discharged is not equal to the soil compression volume. Under the test conditions，volume of pore water discharged is lager than soil compression volume and the difference between the two increases nonlinearly with external pressure. The hydrophilic property of soil has direct influences on the nonlinear relationship and the critical porosity of film water discharged. Based on the test data，relevant function relationships of different soils with different hydrophilic properties are established. The test results can provide reference for related research.

Select

Application of space axisymmetric solutions of cavity expansion to soil squeezing of pile driving

HAN Tongchun1，2，DOU Hongqiang1

2012, 31 (S1): 3209-3215

[PDF] 795 KB (31)

+

Show Abstract

The paper assumed that the process of pile driving is the quasi-static expansion process of cylindrical cavity，and the cylindrical cavity hole and semi-infinite soil body had been assumed as the thick walled cylinder of finite length with the infinite outer radius. Then the stress field and strain field were obtained through Love displacement functions in the elastic region. While the stress field and strain field in the plastic range are got by using the associated flow rule of Mohr-Coulomb and spatial mobilized plane(SMP) yield criterion. Then the calculated results were compared with the theoretical solutions of cylindrical cavity expansion which based on conventional plain strain model. In order to verify the correctness of theoretical solutions，the axisymmetric model of pile-soil was established by ABAQUS，and dynamic explicit integration method and arbitrary Lagrangian- Eulerian(ALE) adaptive meshing were adopted to overcome the large strain and highly distorted grid and other issues in the traditional numerical calculation of driving pile. According to the case，the result shows that the theoretical solution and numerical solution of the expansion of ultimate stress which based on Mohr-Coulomb and SMP yield criterion were good agreement，they all reflected the effect of the depth of driving pile，and the former was more safer.

Select

EFFECT STUDY OF PLANT ROOTS REINFORCEMENT ON SOIL

YU Qinqin1，QIAO Na1，LU Haijing1，HU Xiasong1，2，LI Guorong1，ZHU Haili1

2012, 31 (S1): 3216-3223

[PDF] 1697 KB (26)

+

Show Abstract

The triaxial compression tests have been conducted in cold and arid environments on four samples：soil without roots，herb root-soil composite system，shrub root-soil composite system and shrub root-herb root-soil composite system. By comparing the strength and corresponding stress-strain properties of the four samples，the effects of the roots reinforcement on soil and slope protection have evaluated. The results show that：(1) Under the confining pressure at 20，30 and 40 kPa，the main stress differences of root-soil composite system and soil without roots increase with the growing of axial strain，finally drive to the stable values. The relationship curves of main stress difference and axial strain belong to the strain hardening type. The shear capability of root-soil composite systems increases more quickly than that of soil without roots at the early stage of loading. (2) Under three degrees of confining pressure，the shear strength peaks of root-soil composite system samples are larger than that of soil without root，and the order of the shear strength peaks of the four samples from big to small is caragana korshinskii root-achnatherum splendens root-soil composite system＞achnatherum splendens root-soil composite system＞caragana korshinskii root-soil composite system＞soil without root. (3) Compared with soil without roots, the increasing ratio of cohesion of three root-soil composite system are 94.1%，66.6%，39.2% respectively. The increasing ratio of the combination of Caragana korshinskii root and Achnatherum splendens root-soil composite system is 16.5% bigger than Achnatherum splendens root-soil composite system，39.4% bigger than Caragana korshinskii root-soil composite system. The varying law shows that plant roots have obvious effects on slope reinforcement，especially the combination of herb roots and shrub roots，which owns greater effects than herb roots or shrub roots alone. The achievements can supply theoretical reference for geological catastrophes，such as soil and water loss，shallow landslide in the testing area and other areas with similar natural environments.

Select

STUDY OF PILE GROUP MODEL TEST WITH PRELOADING BOTTOM SEDIMENT

SONG Linhui1，CHEN Jian2，MEI Guoxiong2

2012, 31 (S1): 3224-3230

[PDF] 2641 KB (10)

+

Show Abstract

For reducing the influence of bottom sediment on bearing capacity of bored piles，a method of preloading sediment is proposed based on the principle of pile-soil interaction and the allowable displacement amount for frictional resistance. And the model tests are designed，which studied the bearing behavior of pile group with sediment and without sediment. The model experiment include two-pile foundation，three-pile foundation and four-pile foundation. For pile group without the sediment，the P-s curve of pile group represents step shape between pre-and post compacting the bottom sediment. The settlement of pile is greater after compacting the sediment. And the frictional resistance is greater than the general pile. Meanwhile，with the increase of load，the tip resistance experiences a process of small to great，and finally reaches the normal level. Through transferring the P-s curve of pile with sediment，the pile bearing capacity return to normal after the expense of certain settlement，and close contact between the pile cap and soil due to settlement，making the pile and soil common loading，which finally makes the pile has a higher vertical bearing capacity and a better horizontal bearing performance. The research results can provide a reference for similar projects.

Select

STUDY OF INFILTRATION AND COLLAPSIBLE DEFORMATION LAW OF UNSATURATED LOESS UNDER OVER BURDEN PRESSURE BY USING TDR SOIL WATER PROBE

HUANG Xuefeng1，2，LIU Changling1，YAO Zhihua2，YANG Xiaohui1，ZHANG Shijing1，ZHANG Jianhua3

2012, 31 (S1): 3231-3238

[PDF] 2248 KB (10)

+

Show Abstract

By large-scale in-situ water immersion test in the field of the collapsible loess under over burden pressure，There are TDR moisture probes embedded in different positions and depths，in order to measure the data about infiltration in vertical and horizontal directions. The law of infiltration and collapsible deformation under over burden pressure and their relationships after soaking are researched，the results show that：(1) The law about water infiltration in the soil is the first big pore，then penetrating down to enlarge saturated；(2) In water infiltration process，soil which is above depths of 22.5–25.0 m is more vulnerable to collapse，and soil below depths of 22.5–25.0 m whose soil moisture content increases slowly and reaches hardly collapsible starting moisture contents is not easy to collapse，therefore，the depths not only can be used as critical depth on-site collapsibility evaluation，but also can be considered to be the reference foundation treatment floor depth in large thickness collapsible loess area when the foundation is treated；(3) moisture content change curves which is from TDR soil moisture probe not only can be used to measure volume moisture content changes of time，and can be used to determine whether happen collapsible loess deformation，collapsible sensitivity and variation of collapsible coefficient with depth，and the diffusion speed of the water in the unsaturated loess can also be calculated roughly.

Select

A NEW CALCULATION METHOD FOR LARGE-DIAMETER-TUBULAR-PILE BEARING CAPACITY

LI Yiwen1，LI Boan2，LI Jianqiang2，ZHOU Jian1

2012, 31 (S1): 3239-3244

[PDF] 466 KB (10)

+

Show Abstract

Based on the imperial college pile(ICP) method，a new method is proposed to calculate the bearing capacity of large-diameter-tubular-pile，in which the contribution of soil plug is considered. However the inner pile friction is not taken into account due to the small value，not full-length distributed and conservative consideration. In this approach，the end resistance is the average value of tip resistance from the pile tip to the depth of 2 times of the pile diameter. In view of the unpopularity of ring shear test，the peak value of direct shear test is used for the friction angle of the interface by amplification of 1.2，which is verified through test results. The radial effective stress is very important in bearing capacity calculation，and a simplified method with a few parameters is put forward. This new approach is much simpler than ICP method，and could have satisfactory estimations if compared with α-method，Randolph methods and V&F method. The test results prove that the new method is reliable.

Select

RESEARCH ON LONG-TERM CREEP TEST OF PERMAFROST ON QINGHAI—TIBET PLATEAU

LIU Shiwei1，2，ZHANG Jianming1，ZHANG Hu1，ZHENG Bo3

2012, 31 (S1): 3245-3253

[PDF] 2695 KB (11)

+

Show Abstract

In order to investigate the creep behaviour of permafrost on the Qinghai-Tibet Plateau，long-term creep tests have been performed in permafrost regions at Beiluhe basin，and static load tests were applied. Bearing plate of the platforms is buried near the permafrost table. According to the drilling data，permafrost under the bearing plates belongs to warm and ice-rich frozen soil. Thickness of compressive layer can be determined considering lithology and ice content of frozen soil，and the concept of weighted average water content is also put forwarded. By discussing the ground temperature data，it is found that，within the annual depth of ground temperature，the average temperatures of different depths under the platforms reduces year by year，which implies that frozen ground under the platforms maintains a state of heat releasing due to cooling. Experimental study of the long-term creep test indicates that，temperature variation of the compressive layer is the decisive factor for creep deformation of permafrost. When the temperature increases，the creep rate increases accordingly. Conversely，the creep rate decreases when temperature decreases. When air temperature has little influence on the temperature of compressive layer，creep equation of warm and ice-rich frozen soil can be approximately applied to predict the development of the in-situ creep deformation. The development of creep deformation of permafrost in cold regions has significant influence on long-term stability of engineering structures.

Select

study of seismic softening behavior and ABAQUS simulation of pile-raft-clay system

MA Kang1，2，XU Qiang 2

2012, 31 (S1): 3254-3263

[PDF] 3995 KB (10)

+

Show Abstract

By conducting dynamic centrifuge tests on the pile-raft-clay system，that soil softening will be taken place in both near field and far field clay in a great degree is investigated，which are manifested as an increase in the resonance periods of clay layers with the level of shaking and successive earthquakes，while this is not the case for the pile-raft foundation since resonance periods of raft and bending moment envelopes of the pile are hardly affected by earthquake loadings. Furthermore，pile-raft dynamic behavior is hardly affected by the stiffness degradation of surrounding clay and could keep stable in successive earthquakes process. Then centrifuge tests are back-analyzed by using ABAQUS 6.9. The results show that，which are conducted using Hypoelastic model embedded in ABAQUS and a developed constitutive relationship，gave reasonably good agreement with the experimental observations. The ability of the numerical model to reasonably replicate the centrifuge tests suggested that ABAQUS simulation can be a powerful method to analyze the dynamic behavior of pile-raft-clay system under different conditions which can not be considered in the centrifuge experiments. Moreover，in ABAQUS analysis，the soil model with or without considering degradation can give almost similar results，but calculation using Hypoelastic soil model showed timesaving and speedy advantages.

Select

EXPERIMENTAL RESEARCH OF MECHANICAL PROPERTIES AND MICROSTRUCTURE FOR CEMENT MORTAR COMPOSITE SOIL

WANG Hailong，SHEN Xiangdong，WANG Xiaoxiao，DU Jinsheng

2012, 31 (S1): 3264-3269

[PDF] 2003 KB (11)

+

Show Abstract

Taking cement mortar composite soil in Hetao irrigation district as research object，relationship between amount of mixed sand and the strength is studied，aiming to find the suitable sand amount mixed in the cement mortar composite soil which has good engineering adaptability. Meanwhile，unconfined compressive strength，deformation characteristics and the microcosmic structure of cement mortar composite soil with different amounts of mixed sand and ages are analyzed. The laws of strength and deformation characteristics of cement mortar composite soil are influenced by amount of mixed sand and age of sand are obtained. The results show that，if a certain amount of sand is mixed in the cement mortar composite soil，strength of cement soil improves effectively，as well as structure of cement-soil. There is an optimal amount of mixed sand in the certain cement content which makes cement mortar composite soil having the highest strength and the stress-strain curves all showing peak values.

Select

ANALYSIS OF ONE-DIMENSIONAL NONLINEAR CONSOLIDATION OF SOFT SOIL CONSIDERING EXPONENTIAL FLOW LAW AND NON-UNIFORM DISTRIBUTION OF INITIAL EFFECTIVE STRESS

LI Chuanxun1，2，XIE Kanghe2，HU Anfeng2，LIU Xingwang3，QI Tian4

2012, 31 (S1): 3270-3277

[PDF] 2067 KB (11)

+

Show Abstract

Based on the results of consolidation experiments combining with permeability test，the governing equation of nonlinear consolidation was developed to consider exponential flow law，time-dependent loading and the actual distribution of initial effective stress in actual engineering，and the finite difference solutions for this governing equation were obtained. On condition that exponential flow law was degenerated to Darcy′s law， constant coefficient of consolidation，time-dependent loading and uniform distribution of initial effective stress were considered，the reliability of numerical solutions was verified by comparing the numerical solutions with the corresponding analytical solutions. Furthermore，nonlinear consolidation behavior under different parameters was analyzed. The results show that，if the ratio of the final effective stress to the average value of initial effective stress is less than 2，the rate of consolidation increases under smaller time factor，and decreases under the large long time factor. With the ratio of the final effective stress to the average value of initial effective stress increases，it can be found from the consolidation curves that the rate of consolidation increases with the exponent during the whole process of consolidation. The rate of consolidation with consideration of linear increases of initial effective stress is faster than that with consideration of uniform distribution of initial effective stress. The rate of consolidation increases with loading rate. In addition，both the ratio of the final effective stress to the average value of initial stress and the nonlinear consolidation parameters have greatly influenced on consolidation behavior.

Select

ENERGY DISTRIBUTION AND SEPARATION OF BLAST WAVE BASED ON TIME-FREQUENCY ENERGY ANALYSIS TECHNOLOGY

ZHAO Jianping，LIN Hang

2012, 31 (S1): 3278-3285

[PDF] 1120 KB (10)

+

Show Abstract

Blast wave signal measured in a set of concrete was analyzed using short time Fourier transform (STFT)，continuous wavelet transform(CWT) and Wigner-Ville distribution(WVD). Then the distribution and characteristics of energy density of blast wave were obtained quantitatively by time-frequency analysis. And the adaptability of the three methods to analyze non-stationary blast wave signals was compared and the blast wave energy of different regions was calculated on the time-frequency spectrum. The results show that the blast wave signal in the whole time-frequency map shows two zones，i.e.(3–9 μs，19–720 kHz) and (14–25 μs，19–150 kHz)，and the energy density of the two zones is significantly different. The first zone has the characteristics of high-frequency，high energy density，very short duration of action and significant energy，while the second zone has relatively low frequency and energy density，a longer duration of action and larger energy. WVD is more adaptive to the high and low frequency resolution of blast wave and the precision of energy calculation than the other methods. The energy of the first zone is 54.5% of the total energy，and the second zone accounts for 29% by using the WVD method.

Select

CALCULATION OF PILE-SOIL STRESS RATIO OF TWO-DIRECTION REINFORCEMENT COMPOSITE FOUNDATION UNDER EMBANKMENT LOADS

ZHAO Minghua，LIU Meng，LONG Jun，GU Meixiang

2012, 31 (S1): 3286-3290

[PDF] 604 KB (10)

+

Show Abstract

According to the characteristics of interaction among embankment，reinforced cushion and pile-soil reinforced area，the reinforced cushion is regarded as an elastic thin plate，and the soil and pile are simplified as a series of springs with different rigidities. Based on the theory of small deflection thin plate on elastic foundation，with consideration of soil arching effect in the embankment，the deflection deformation of the cushion is simulated. The calculation model for two-direction reinforcement composite foundation under embankment loads is established. Based on the model and the continuous conditions of stresses and deformations，the solution to pile-soil stress ratio can be obtained. Finally，the result calculated by the proposed method is compared with the observed one of a project. It is shown that the calculated result is close to the observed one. It verifies the feasibility of the proposed method and the results can provide references for engineering practice.

Select

FIELD PULL-OUT TEST RESEARCH ON TENSION AND PRESSRUE UNBONDED ANCHOR CABLES

SHEN Jun，GU Jincai，ZHANG Xiangyang，CHEN Anmin，MING Zhiqing

2012, 31 (S1): 3291-3297

[PDF] 1788 KB (11)

+

Show Abstract

The shear stress distribution curves of tension and pressure unbonded anchor cable between grouting body and rock hole wall，and the shear stress distribution curves of tension anchor cable between grouting body and steel wires are given；then，the shear stress distribution laws along the grouting body length are obtained by field pull-out tests. The tests results show that，for the tension anchor cable，shear stress peak value between grouting body and rock hole wall is less than that between grouting body and steel wires，but the shear stress distribution length is longer and the peak value point locates in back grouting segment. The shear stress between grouting body and rock hole wall is not equally distributed no matter what the anchor cable type is，and the peak value point locates at different grouting segment positions. For the pressure anchor cable，shear stress peak value is large and the distribution length is short and shear stress decays quickly under the same load. The effective bonded length of tension anchor cable increases significantly with the increasing resisting load. On the other hand，the shear stress peak value of pressure anchor cable increases significantly with the increasing resisting load. The bearing capacity of tension anchor cable is constant and it is normally adopted when requiring lower bearing capacity，the key construction is ensuring the grouting length. The bearing capacity of pressure anchor cable is in proportion to the number of the pressure bearing segment and it is adopted when requiring higher bearing capacity，the key construction is ensuring the grouting fullness and avoiding the grouting body shrinkage.

Select

DETECTION AND FORECASTING FOR HIDDEN DANGER OF KARST FISSURE WATER AND OTHER GEOLOGICAL DISASTERS DURING CONSTRUCTION OF TUNNELS AND UNDERGROUND PROJECTS

ZHONG Shihang1，2，3，SUN Hongzhi4，LI Shucai2，LI Xiu5，WANG Rong3

2012, 31 (S1): 3298-3327

[PDF] 14867 KB (9)

+

Show Abstract

There exist numerous unknown things in the construction of tunnels for railways，highways and water transmission，especially in geological conditions. Now the situation in safe construction of projects is extremely serious，more and more requirements have been put forward for prediction of geology during tunnel construction. Greatly progress in theories，technologies and practices for surveying forward from working face during tunnel construction have been gained in support of government departments since 1990，especially after 2003，who pay more attention on the increasing effect of survey and forecast，technology development and innovation，and independent intellectual property. Several majors and institutes have been centralized to that research. The technology and method including landsonar，transient electromagnetic methods(TEM)，ground penetrating radar (GPR)，and IP method，have achieved better effects in research of theories and practices on overcoming difficult problems about faults，groundwater，karst caves and underground rivers，and on determining their accurate spatial locations.

Select

STUDY OF COMBINATION EVALUATION OF SURROUNDING ROCK QUALITY CLASSIFICATION OF GUANKOUYA TUNNEL

CAO Wengui，ZHAI Youcheng，WANG Jiangying

2012, 31 (S1): 3328-3332

[PDF] 342 KB (30)

+

Show Abstract

Sometimes，the evaluation results given by different tunnel classification methods of surrounding rock quality are inconsistent，then combination evaluation idea was introduced. Firstly，a calculation model of surrounding rock quality classification based on combination evaluation was formulated，in which three existing tunnel classification methods of surrounding rock quality are selected as the fundament methods. Secondly，according to the physical meaning and dimension of evaluation indices of different fundament methods were different，a standardized method for evaluation indices was developed to make evaluation results of different fundament methods can compare with each other. Thirdly，a reasonable degrees measure method for fundament methods was established by introducing drifting degree，based on which the weight calculation method for fundament method was developed. Then the combination evaluation method of surrounding rock quality classification of tunnel was developed. Finally，the method was used to analyze the practical engineering，and the results showed that the method proposed here was feasible and reasonable.

Select

EXPERIMENTAL RESEARCH ON ENGINEERING CHARACTERISTICS OF AQUEOUS POWDERY SOIL

SU Yonghua，ZHAO Minghua，LIU Xiaoming，ZHAO Zhenyong

2012, 31 (S1): 3333-3338

[PDF] 2275 KB (8)

+

Show Abstract

Using road tester as main loading instrument and geotextile with good permeability as the cushioning layer，the aqueous powdery soil from Puyang county in alluvial champaign area by Yellow River is taken as test samples；and the mechanical characteristics of powdery soil as bank or dam or roadbed reclamation material are researched roundly through particle size analysis，standard compaction test，static compaction test，shear strength test，seepage test，and compression test in laboratory. The research results indicate that：(1) Compaction curve of powdery soil with poor gradation has a multi-peak values phenomenon. Their compaction performance cant be decided by the particle gradation completely，also is related with liquefaction limit. (2) The internal friction angle changes of powdery soil is lesser when soils saturation is between 50% and 80%，but it changes fiercely when its saturation is bigger than 80% or less than 50%. (3) Compacted powdery soil concurrently has the characteristics of sandy soil and clay. Penetration coefficient of powdery soil increases with silt content. (4) Under the load function，most of settlement for the compacted powdery soil occurs in a short time after the loads added，which is related with mineral components and has no significant relation with pore ratio.

Select

MEASUREMENT AND ANALYSIS OF 3D GEOSTRESS AT UPPER TAMAKOSHI HYDROPOWER STATION IN NEPAL

WANG Jianxin1，GAO Chengyu2，GUO Qiliang1，LIU Xiaoli3，YANG Ye2

2012, 31 (S1): 3339-3344

[PDF] 1095 KB (8)

+

Show Abstract

Geostress measurement was conducted in the south of Himalayas for the first time. 3D hydraulic fracturing method was adopted to measure the geostress at Upper Tamakoshi hydropower station in Nepal. The results are reliable in comparison with the related overseas study. The major principal stress 1 in this field is 17.00 MPa，approximately in NS direction，and small dip angle means its orientation of action is almost horizontal. The intermediate principal stress 2 is 13.39 MPa，approximately in EW direction. The minor principal stress 3 is 8.07 MPa，its azimuth and dip angle indicate that the trend of 3 points down. All of these results prove the combined action of crustal stress and rock gravity. The conclusion of medium-high stress state in this field was drawn according to the ratio of rock mass strength to stresses. The stress tensor characteristics parameter was calculated，which indicates that the geostress field has the characteristics of compression-shear. The larger shear action is one of the main factors that induce frequent tectonic movements. The work is helpful for full understanding of stress state in this field. Furthermore，all these data are greatly important for analysis of fault activity and crustal movement in south of Himalayas mountain.

Select

STUDY OF CHARACTERISTICS OF SATURATED SOFT CLAY UNDER UNIAXIAL CYCLIC LOAD

LIU Tianjun1，2，GE Xiurun2，AN Guanfeng1

2012, 31 (S1): 3345-3351

[PDF] 1962 KB (62)

+

Show Abstract

High liquid limit and low liquid limit clay specimens from Pearl River delta are used for cyclic triaxial tests under uniaxial cyclic loading，respectively，to simulate traffic loads. The emphasis is put on the development of axial strain and pore pressure of saturated soft clay. The influence of axial stress，confining stress and plasticity index are taken into account. The results of tests indicate that：(1) For the same soil，there are different critical cyclic stresses of saturated soft clay under different confining pressures. Critical cyclic stress ratio can be introduced under uniaxial cyclic loading. The critical cyclic stress can be normalized with undrained shear strength of saturated soft clay under different confining pressures. (2) Whether the cyclic stress is greater than the critical cyclic stress，variations of axis strain and pore pressure with number of cycles show two kind of rules. (3) The critical cyclic stress ratio is related to the plasticity index of saturated soft clay. The greater the plasticity index is，the smaller the critical cyclic stress ratio is. (4) When the cyclic stress is less than the critical cyclic stress，with the same loading condition，the axis strain and the pore pressure of samples with greater plasticity index develop faster than those of samples with smaller plastic index. (5) When the cyclic stress is greater than the critical cyclic stress，the sample of saturated soft clay fails rapidly. When the sample fails，the pore pressure can not achieve the value of confining pressure，only 60%–70% of the confining pressure. These conclusions are helpful for analyzing the settlement of saturated soft foundation under traffic loading.

Select

MODEL EXPERIMENT AND ANALYSIS OF WEDGE-SHAPED CUTTING MILLISECOND BLASTING

YUAN Wenhua1，2，MA Qinyong2，HUANG Wei2

2012, 31 (S1): 3352-3356

[PDF] 1967 KB (16)

+

Show Abstract

Aiming at problems of bad cutting effect，low hole utilization for hard rock excavation in coal mines，different cutting model tests were conducted by using concrete as similar material. Different blasting effects were analyzed from the cutting volume，blasting hole utilization and fragmentation. Wedge-shaped millisecond cutting was adopted in which middle blasting holes are 200 mm deeper than other cutting holes with 1or 2 branches explosives and 2 sections of millisecond electric detonator. The experimental results indicate that middle blasting holes increase free surface and overcome rocks clips；and the millisecond blasting extends the delay time of detonation gas with a rational broken particle size and even lump size，then enhances the blasting hole utilization and cutting volume.

Select

SAFETY ISOLATION LAYER THICKNESS AND ACOUSTIC EMISSION MONITORING OF CAVITY UNDER OPEN PIT BENCHES

LIU Xiling，LI Xibing，GONG Fengqiang，LI Diyuan

2012, 31 (S1): 3357-3362

[PDF] 494 KB (13)

+

Show Abstract

There have many open pits in China threatened by cavities under open pit benches because of former unreasonable underground mining. Shape and size of these cavities were greatly changed through many years mining activity. There have no clear figures or data to show how these cavities occurred. This would greatly restrict high-efficient and safe mining. Thus，the reasonable safety isolation layer thickness of cavity should be properly calculated，and the feasible stability monitoring method for this kind of cavity should be employed to well ensure safety of personnel and equipments on open pit benches. Based on the present situation of Sandaozhuang open pit of Luoyang Luanchuan Molybdenum Group Inc.，which has lots of cavities under its benches，the safety isolation layer thickness corresponding to different roof spans，which can provide a primary evaluation for cavity stability，was obtained through numerical modeling. Acoustic emission technique was used to monitor the cavity stability. Monitoring data of four types of cavity，i.e. unstable cavity，stable cavity，cavity with drill and cavity after blasting，which are all the typical ones under open pit benches，were listed. The signals of acoustic emission of those cavities were analyzed to obtain acoustic emission characteristics of typical cavities under open pit benches. This will provide reference for following accurate stability evaluation of cavities under open pit benches that are monitored by acoustic emission technique. Thereupon，the efficient safety guarantee system of open pit benches with cavity would be established through primary evaluation according to safety isolation layer and stability monitoring by the acoustic emission technique.

Select

SHPB TEST AND ANALYSIS OF DYNAMIC TENSILE PERFORMANCE OF SANDSTONE UNDER HIGH STRAIN RATE

PING Qi1，MA Qinyong1，ZHANG Jingshuang1，YUAN Pu1，CHEN Baisheng2

2012, 31 (S1): 3363-3369

[PDF] 1333 KB (16)

+

Show Abstract

In order to investigate the dynamic tensile performance of mine sandstone under high strain rate，variable cross-section split Hopkinson pressure bar(SHPB) apparatus is used to measure both the dynamic tensile stress and the strain rate of specimens. Rock samples are processed into disc specimens with the thick-diameter ratio of 0.5. Six impact pressures loaded in radial direction are applied in splitting tests to implement various loading speeds. The results show that not only splitting failure mode of tested specimens meets the validity condition in Brazilian disc test，but also radial stress distribution in specimen achieves the stress homogenization demand. Both the actuall measured waves and the strain rate effect are analyzed. The tensile stress and the strain rate of specimens under high strain rate are also studied. When the impact pressures are in the test range and the average strain rate increases from 48 to 137 s－1，the relationship between the average strain rate and the impact pressure is approximately an logarithmic function，and that between the dynamic tensile strength and the average strain rate is close to a power function.

Select

MODEL TEST RESEARCH ON EARTH PRESSURE OF UNDERGROUND RETAINING WALL OF CONVENTIONAL ISLAND IN A NUCLEAR POWER STATION

YUAN Jie1，2，GU Renguo1，2，FANG Yingguang1，2，FENG Weixi1，2

2012, 31 (S1): 3370-3376

[PDF] 5298 KB (18)

+

Show Abstract

Taking the stepped concrete arch retaining wall of the conventional island in Guangdong Taishan Nuclear Power Station as the prototype，1∶10 experiment model is established according to the similarity theory. The distributions of earth pressure，displacement and water pressure of stepped vertical wall structure and stepped arch wall structure at different slope gradients and working conditions are comparatively studied. The results show that：(1) The earth pressure of retaining wall of the two structural forms satisfy nearly linear distribution under various work conditions. The bigger the buried-depth is，the greater the value of measured earth pressure becomes. And the earth pressure value is generally less than the theoretical values of the Rankine earth pressure and static earth pressure. At the same time，the additional stress is produced in different ranges of depth under loads，which is 0.5–2.5 kPa. (2) The measured displacement decreases as the depth increases，and is not affected by construction loads. Under certain work conditions，the displacement at the top of retaining wall reaches its maximum value. Under various work conditions，the displacement reaches the maximum value without slope limitation，otherwise，the displacement becomes less when the slope angle becomes greater. (3) The distribution and size of measured water pressure are basically identical to the theoretical ones，and the influence of construction loads can also be ignored. (4) Under various work conditions，the earth pressures at buttress and arched slab of stepped arch wall structure are less than those of stepped vertical wall structure，and the difference is 0–3 kPa. But the distribution and size of displacement and water pressure of the two structural forms are basically identical. The conclusions will have certain reference values for similar engineering design and construction in future.

Select

EFFECT OF SHIELD TUNNEL UPLIFT CAUSED BY BACK-FILLED GROUTING ON STRUCTURE

ZHU Ling1，2，DING Wenqi1，2，YANG Bo1，2

2012, 31 (S1): 3377-3382

[PDF] 997 KB (27)

+

Show Abstract

As an essential procedure，the quality of back-filled grouting directly affects not only the deformation of strata around the tunnel but also the uplift of lining structure. Based on the present longitudinal equivalent continuous model theory and the elastic foundation theory，a longitudinal analysis model was designed. It can be obtained by numerical simulation of finite element method(FEM) that the largest deformation happens nearby the tenth lining ring. An important parameter，the maximum splaying amount of the joints，was used to analyze the effects of soil reaction coefficient，amount of longitudinal bolts，advance rate and width of rings. The following conclusions can be drawn. (1) The maximum splaying amount decreases with the increase of soil reaction coefficient and amount of longitudinal bolts，and increases obviously with the increase of advance rate and width of rings. (2) It is advisable to improve the soil reaction coefficient through artificial methods only when the soil is quite soft.

Select

DEFORMATION MONITORING AND ANALYSIS OF RETAINING STRUCTURE IN FOUNDATION PIT OF PINGAN FINANCIAL CENTER IN SHENZHEN

JIANG Chong，ZHOU Keping，HU Yifu

2012, 31 (S1): 3383-3389

[PDF] 2624 KB (12)

+

Show Abstract

Taking the foundation pit of Pingan Financial Center in Shenzhen as background，deformation monitoring scheme is designed according to the characteristics of retaining structure of the foundation pit. The data of retaining structure deformation monitored at field are analyzed，focusing on the variation in horizontal deformation of the retaining structure with excavation depth of foundation pit and time，the change in axial force of steel support with time during the process of foundation pit excavation. The results show that the design is safe. According to the monitoring data of surface subsidence，the change in surface subsidence induced by the excavation of the foundation pit is analyzed. It is concluded that the surface subsidence can be divided into four stages，i.e. linearly increasing stage of settlement，continuous stage of settlement rate，declining stage of settlement rate，and approximately steady stage of settlement. Based on this，the Usher model for settlement prediction is introduced to establish the prediction model for surface subsidence. Measured data agree well with the predicted values，showing that the method is feasible.

Select

SIMPLIFIED ANALYTICAL METHOD FOR RESPONSE PREDICTION OF SINGLE PILE EMBEDED INTO LAYERED SOILS

ZHANG Qianqing1，LI Lianxiang2，LI Shucai1，LI Liping1

2012, 31 (S1): 3390-3394

[PDF] 1270 KB (8)

+

Show Abstract

A simplified approach for nonlinear analysis of response of a single pile embedded in layered soils is presented. Two models are adopted in the proposed approach. One model uses a softening nonlinear relationship to simulate the degradation behavior between unit skin friction and pile-soil relative displacement developed along the pile-soil interface，and the other model adopts a hyperbolic relationship to capture the pile end response. Based on the two proposed models，a highly effective iterative computer program is developed for the analysis of single pile response. The efficiency and accuracy of the presented method is verified by using a series of field tests. Furthermore，a parametric study shows that the settlement of the single pile decreases with increasing failure ratio of skin friction，and increases with increasing failure ratio of tip resistance. It also can be concluded that the value of pile-soil relative displacement at the ultimate skin friction has a small influence on the single pile response derived from the proposed softening model of skin friction.

Select

EXPERIMENTAL INVESTIGATION ON MECHANICAL PROPERTY OF REINFORCED FRACTURED ROCK

JIN Aibing，WANG Zhikai，MING Shixiang

2012, 31 (S1): 3395-3398

[PDF] 770 KB (12)

+

Show Abstract

Fractured rock is often encountered in the process of underground construction，and intact rock can also be broken under the condition of high stress or other factors. The fractured rock has the properties of high rock strength but low rock mass strength，and it can keep high bearing capacity after being effectively reinforced. The mechanical characteristics of intact rock and fractured rock reinforced by grouting and bolt-grouting，respectively，were studied in laboratory. And the information about strength recovery of reinforced fractured rock was gained. The experimental results show that the compressive strength of the grouting reinforced fractured rock sample can recover to 40%–50% of the intact rock，and has no residual strength. The compressive strength recovery rate of bolt-grouting reinforced fractured rock sample is a little larger than that of the grouting reinforced fractured rock sample，and the residual strength is obviously improved.

Select

A METHOD FOR CALCULATING UNLIMITED EARTH PRESSURE OF RETAINING WALL WITH TRANSLATION MODE

YANG Qingguang，LIU Jie，HE Jie，LUO Shanhuang

2012, 31 (S1): 3399-3406

[PDF] 1752 KB (27)

+

Show Abstract

Considering the movement effect of translation mode，the friction angle reduction coefficient and the method of bevel-layer analysis，a method for calculating the unlimited active and passive earth pressures is deduced for cohesiveless soil retaining wall with translation mode. In order to validate the feasibility of the proposed approach，two model tests for active and passive earth pressures were conducted in laboratory，respectively；and the proposed method was used to analyze the two models. Experimental and theoretical results indicate that the curve of active earth pressure increases firstly and decreases then along the depth of retaining wall with different values of s/sc，and it has a point of intersection with the curve of Coulomb active earth pressure at the depth of 0.6H，where H is the wall height. The passive earth pressure keeps increasing along the depth of retaining wall and is always smaller than the Coulomb passive earth pressure. Further study indicates that the action point position of the active earth pressure is higher than that of the Coulomb passive earth pressure，and the action point position of the passive earth pressure is lower than that of the Coulomb passive pressure. Moreover，with the increasing value of s/sc，the calculated and measured action point positions keep away from the action point position of the Coulomb earth pressure.

Select

EXPERIMENTAL STUDY OF DYNAMIC CHARACTERISTICS OF SAND FOR HIGHWAY SUBGRADE

DONG Cheng1，2，LI Zhiyong2，YUE Zhiping2，LENG Wuming1

2012, 31 (S1): 3407-3412

[PDF] 1979 KB (8)

+

Show Abstract

To investigate the dynamic characteristics of sand for highway subgrade under repeated loads，a series of dynamic triaxial tests were carried out. According to the changing rule of accumulative plastic strain with loading cycles，the critical dynamic stress of sand under different compaction degrees and water contents were obtained. The experimental results demonstrate that dynamic resilient modulus values of sand increase with the increase of confining pressure and compaction degree，but decrease with deviatonic stress and water content. The dynamic resilient modulus constitutive model，which reflects the effects of bulk stress and deviatonic stress，was utilized for regression analysis of experimental data. A large coefficient of determination shows that the model is accurate and credible. The prediction model can provide parameters for pavement design based on dynamic method. In order to evaluate subgrade filling according to the above mentioned dynamic characteristics，the design principles for highway subgrade were put forward based on the dynamic characteristics of sand.

Select

MONITORING AND ANALYSIS OF EXCAVATION-INDUCED SUBSIDENCE OF SUBWAY STATION CONSTRUCTED BY ARCH COVER METHOD AND CONTROL MEASURES

ZHANG Guangquan1，2，DU Zijian3，SONG Jinquan2，CAI Jiande2，TAO Tiejun1，2

2012, 31 (S1): 3413-3420

[PDF] 2515 KB (7)

+

Show Abstract

Zhongshan Park Station of Qingdao subway line No.3，which is constructed by arch cover method，locates in soil-rock composite layer. The maximal excavation depth is about 27.24 m. Upper overburden is composed of quaternary and highly weathered granite，and the lower part is consisted of medium-slightly weathered granite and granite-porphyry. The thickness of partially highly weathered rock layer is large and the medium-slightly weathered rock surface is partly steep，which makes the contact surface unstable. To ensure the excavation work，the ground subsidence was monitored and analyzed at the station. Results indicate that the subsidence emerges before the tunnel working face reaches to about 20 m in front of monitoring sections when the arch cover method was adopted. With the decrease of distance between the tunnel working face and monitoring sections，the subsidence velocity continues to increase. Generally，the value of subsidence is 7–15 mm when the excavation face was going through the monitoring sections. The velocity of ground subsidence increases to the maximum until the working face passes through the monitoring sections for 5–10 m. After the working face passes through the monitoring section for more than 10 m，the subsidence velocity begins to fall. Most of observation points have the trend to be stable after the working face passes through the monitoring sections for about 20 m. Supporting should be exerted and closed as early as possible to make sure that the supporting can play a good role. In addition，there is a interrelationship between the left and right pilot tunnels. It is indicated that the appropriate distance between the left and right pilot tunnels should be 2.5 times of the diameter of pilot tunnel. According to the monitoring and analysis results，a series of control measures are put forward，which are proved to be feasible and effective by practice.

Select

CASE STUDY OF PILE BEARING CAPACITY TEST AT LIHE RIVER AQUEDUCT OF SOUTH-TO-NORTH WATER TRANSFER PROJECT

FAN Ling1，2，PENG Shuquan1，YIN Xiaobo3，4，WEI Jun2，GUO Qiwu4

2012, 31 (S1): 3421-3427

[PDF] 2450 KB (9)

+

Show Abstract

The designed bearing capacity characteristic value of 62 m long frictional pile in Lihe River aqueduct of South-to-North Water Transfer Project is 14 108 kN. The bearing capacity tests are conducted by combining self-balance method with high-strain method. With the self-developed high-strain hammer system is developed， several significant parameters are gained，including the recommended lateral friction of rock and soil layers，the recommended pile end resistance，the pile head displacement and the ultimate bearing capacity of single pile. The results of self-balance method and the high-strain method are much close，and they can verify each other. The high-strain hammer system is reasonable and effective for pile tests. The test results have reference values for similar projects.

Select

DEVELOPMENT AND QUICK-PREPARING OF CONTROLLABLE CLAY CEMENT STABLE SLURRY ADAPT TO ANTI-SEEPAGE GROUTING IN DEEP COMPLEX ROCK AND SOIL STRATUM

ZHANG Guijin1，YANG Songlin2，CHEN Anzhong3，ZHANG Qun2

2012, 31 (S1): 3428-3436

[PDF] 2613 KB (23)

+

Show Abstract

With the marked difference of the groutability in one borehole of the deep complex rock and soil stratum，grouting materials must change accordingly and grouting methods should enjoy great suitability. The present grouting materials is short of controllability and groutability. In the present grouting method，the density changes gradually in every length of grouting section which makes the grout scattering difficult to control，the grout wasteful to discard and the work efficiency low. Considering the practical needs of the construction technology in the grouting process and the performance optimization of the grouting materials，a controllable stable slurry is made mainly from clay and cement which is developed by taking advantages of the good performance of the clay，very low plastic viscosity and yield strength of sodium silicate slurry，the traits of cements solidification and strength，and modifier through the laboratory test of large-sample. The performance of this kind of slurry satisfies the general needs of the anti-seepage engineering，besides，the rheological parameter，setting time and concretion parameters can be adjusted on a large scale. As for the complex stratum，the tested controllable grouting materials and corresponding means of providing the materials can be selected according to the differences of the characteristics of grouted rock and soil，which can realize quick preparation of the grouting materials during the process and make the grouting easier，the discard grout few and the cost lower. The completed grouting test in the anti-seepage curtain engineering at river bend plot of Tuokou hydropower station indicated that compared with the traditional grout and grouting method，the injection volume has reduced about 65%，the efficiency of the rigmonth(m/(rig·month)) has increased about 30%；and the grouting quality meets the design requirements. Hence the research result can be widely applied to the project as well as other similar ones.

Select

DEFORMATION AND FAILUER MODEL TEST OF MODERATE-SLOW DIP EXCAVATION BEDDING SLOPE UNDER ACTION OF SEISMIC LOAD

A Fayou1，KONG Jiming2，NI Zhenqiang2

2012, 31 (S1): 3437-3443

[PDF] 3762 KB (13)

+

Show Abstract

In the Wenchuan earthquake disaster area，moderate-slow dip bedding slope is a kind of slope that seismic mountain disaster is very developing and the slope earthquake disaster is often exacerbated by the excavation. According to the survey，integral sliding is the main deformation and destruction form of moderate- slow dip bedding slope. In order to reproduce the process and analysis regularity of slope deformation and failure under the action of seismic load，Magunyan landslide located in Beichuan County is chosen as the typical example of moderate-slow dip excavation damage bedding slope；and the indoor physical model test of slope deformation and failure under the action of seismic load are carried out. The results show that slope deformation and failure under the action of seismic load is intensified by the excavation. Integral sliding is the main form of deformation and failure；and the results are consistent with field investigation. From the whole process of deformation and failure of bedding slope，the slope can be divided into the three stages：(1) Initial phase of the earthquake. The slope gradually breakthrough and slightly cuts out along the discontinuous bedding plane induced by excavation，and large cracks appear at the top of excavation slope. (2) Shallow landslides phase at top of excavation slope；(3) Integral sliding phase.

Select

DYNAMIC DEVELOPMENT CHARACTERISTICS OF TWO ZONES OF OVERBURDEN STRATA UNDER CONDITIONS OF COMPOUND ROOF，HIGHLY GASSY AND THICK COAL SEAM IN FULL-MECHANIZED TOP COAL CAVING FACES

GAO Baobin1，2，WANG Xiaolei3，ZHU Mingli3，ZHOU Jianwei1，2

2012, 31 (S1): 3444-3451

[PDF] 3211 KB (19)

+

Show Abstract

Taking Yuwu coal company as the experimental mine，by using the equipment which is sealed two ends by capsules in borehole，affused measurable water between the two capsules and borehole televiewer system，overburden two zones height of fully-mechanized top caving are monitored and analyzed through the digital relationship of fractures around mining such as change of dip angle， numbers and depth，numbers and width. At the same time， similarity model and numerical model experiment of fissure development evolution are carried out. The results show that：(1) Caving zone height changes from 27 m to 32 m and fractured zone height changes from 58 m to 61 m；(2) The fracture characteristics are mainly with high angle and low width before mining，with small angle and middle width after mining；with the mining of working face，the numbers of fractures increase with straight line；(3) The fractures cluster region mainly focuses near the coal wall，and the fractures density distribution curves of overlying strata are high at two ends and middle of working face，just like wave-shapes.

Select

ANALYSIS OF INFLUENCE ON DEFORMATION OF ADJACENT SUBWAY TUNNEL DUE TO BILATERAL DEEP EXCAVATIONS

WU Shangyong1，2，YANG Xiaoping1，2，LIU Tingjin1，2

2012, 31 (S1): 3452-3458

[PDF] 3543 KB (14)

+

Show Abstract

According to the practice of deep excavation adjacent to subway tunnel in Guangzhou，the finite element software Midas/GTS is employed to establish a 3D numerical model to simulate and analyze the interactive impact on the crossing tunnel caused by different construction sequences of the adjacent deep excavations on both sides of the tunnel. A comparative analysis is also made between the measured data and the results of finite element method. The calculated results are good agreement with the field measurements. The two results show that symmetric excavation method is better than asymmetric excavation method in controlling the horizontal displacement of the tunnel；however，symmetric excavation method is not suitable for controlling the vertical displacement of the tunnel. A conclusion is proposed and verified by numerical experiment that the effect on the curved tunnel in the horizontal plane caused by unload on the convex side of the curved tunnel is more serious than that by unload on the concave side of the curved tunnel under the same condition，because the longitudinal stiffness is different in two sides of the curved tunnel.