Select

2011, 30 (S2): -3377
Full Text:

[PDF 0 KB] (716)

+

Show Abstract

Select

STUDY OF CONTACT PRESSURE BETWEEN PRIMARY LINING AND SECONDARY LINING FOR TUNNELS OF PASSENGER DEDICATED LINES

FANG Qian1，2，ZHANG Dingli1，WONG Louis Ngai Yuen2，LI Pengfei1，CHEN Tielin1

2011, 30 (S2): -3385
Full Text:

[PDF 0 KB] (931)

+

Show Abstract

To systematically study the mechanical properties of the secondary lining for tunnels of the passenger dedicated lines(PDL)，in-site monitoring is used to measure the contact pressures between the primary lining and the secondary lining for some typical tunnels of different Lines，such as Guiguang Line，Lanyu Line and Jinghu Line. According to the research，the contact pressure reaches its maximum value at the moment when the tunnel lining trolley is removed. The load acting on secondary lining is the actual deformation pressure，which is totally different from the loose pressure prescribed in Chinese tunnel criteria. The safety factor for secondary lining under the measured load is higher than that under the criteria load and satisfies the safety requirements. It is therefore possible for the primary lining to sustain the entire surrounding rock pressure with the help of necessary auxiliary method and suitable installation time. The result given in this research enhances our understanding towards the mechanical characteristics of secondary lining for the PDL tunnel and it will be helpful for secondary lining design.

Select

MODEL TEST ON INFRARED RADIATION FEATURE OF TUNNEL SEEPAGE AND IMAGE PROCESSING

DOU Haitao1，2，HUANG Hongwei1，2，XUE Yadong1，2

2011, 30 (S2): -3391
Full Text:

[PDF 0 KB] (780)

+

Show Abstract

To study the infrared radiation(IR) features of water seepage in tunnel，water seepage is simulated on an outdoor concrete wall model and IR is measured using an IR thermal imager. The image feature of water seepage is extracted from IR image with a program written in MATLAB. The general experimental results of water seepage show that：thermal image shows temperature field characteristics of high-temperature region surrounded by low-temperature region and a clear interface of water seepage and concrete basement with large temperature gradient. The experimental results of water seepage process show that：the larger water seepage flow is，the larger temperature difference between water seepage and concrete basement is，the more uniform temperature in water region is and the more intense temperature in the water seepage region edge is. The experimental results are useful for water seepage detection and forecasting on concrete projects(such as geotechnical engineering，tunnels，etc.). For IR image features of water seepage，the seepage area and other information are extracted from IR image with a program written in MATLAB. The results lay the foundation for software system development of tunnel water seepage detection on movement.

Select

DYNAMIC SUB-MODEL METHOD OF EARTHQUAKE RESPONSE ANALYSIS OF LARGE-SCALE UNDERGROUND CAVERNS

2011, 30 (S2): -3400
Full Text:

[PDF 0 KB] (735)

+

Show Abstract

The overburden depth of underground caverns in hydropower plants is always huge. When earth surface is considered in mesh discretization，the computation cost is considerable and the computation lowers analysis efficiency. To solve this issue，the dynamic sub-model method is proposed for earthquake response analysis of large-scale underground caverns. This method separates large-scale，coarse-grained calculation of underground seismic motion and small-scale，fine-grained calculation of structural dynamic analysis by performing calculation on seismic field wave model and structural analysis model，respectively. Firstly，based on the transmitting characteristics of seismic wave in deep bedrock，the acceleration data in deep rock mass are estimated by linearly reducing the time-history of ground acceleration data. By inputting the estimated acceleration data along bottom boundary，seismic wave field covering wide range is derived. Afterwards，boundary points of structural analysis model are interpolated in seismic wave field model. The boundary conditions of structural model are then obtained and the earthquake input of structural model is realized. The numerical example indicates that the estimated acceleration data at the bottom boundary take specific engineering conditions into consideration. Therefore the estimated results are more efficient in reflecting actual underground seismic motion than the fixed reduction coefficient in design codes. Meanwhile，the simulation of earth surface reflection of seismic wave has considerable influences on the accuracy of calculation results. The proposed dynamic sub-model method not only guarantees the accuracy of calculation results but also ensures that the earth surface needs not to be modelled. The computation cost is therefore lowered considerably and the computation efficiency is greatly enhanced.

Select

EXPERIMENTAL STUDY OF INFLUENCES FOR WATER CONTENT IN COALBED GAS RESERVOIRS ON METHANE SEEPAGE

YIN Guangzhi1，2，3，JIANG Changbao1，2，3，XU Jiang1，2，3，PENG Shoujian1，2，3，LI Wenpu1，2，3

2011, 30 (S2): -3406
Full Text:

[PDF 0 KB] (859)

+

Show Abstract

The studied specimen was briquettes molded by coal from 3# coalbed of Zhaozhuang coal factory，Jincheng Coal Industrial Company. An experimental plan was designed to test the influence of water content on methane permeability. By using self-developed “coal containing gas thermal-hydrological-mechanical(THM) coupling experimental equipment”，the change rule of water content effects permeance of coalbed methane was studied. The research results showed that：under the conditions of constant temperature and effective stress but different water contents，the methane effective permeability increased with the decreasing of water content in coal. In the range of water content tested in this experiment，the relationship between water content of coal and methane effective permeability could be expressed by a linear function. The water in coalbed gas reservoirs occupies space of permeance pores in coal seams and decreases methane transportation passages which makes the transportation difficulty. According to the analysis of experimental results，it is theoretically proven that to wet the coal by pouring water could be used as a measure to prevent coal and gas outburst.

Select

STUDY OF REASONABLE CONTROLLING RANGE OF BOTTOM-HOLE PRESSURE IN INITIAL STAGE FOR COAL BED METHANE PRODUCTION

WANG Zhiyin，DUAN Pinjia，ZHANG Huabin

2011, 30 (S2): -3412
Full Text:

[PDF 0 KB] (798)

+

Show Abstract

Reasonable bottom-hole pressure is closely related to the mechanical properties of coal rock and the stress distribution around the well，and there is an interdependent relationship between the stress distribution around the well and the pass-through cracks which can increase the absolute permeability. Firstly，based on the experimental results of coal rock in Hancheng，the varying law of the absolute permeability with the different stress states around the well is analyzed in this paper. And then，according to the elastic-plastic theory and through the elastic-plastic analysis to the rock around the well of fissures，the mathematical models on the relationships between the stress around the well and the bottom hole pressure are established. Finally，the reasonable range of the bottom hole pressure is obtained to maintain or improve the absolute permeability，and to be applied in the practical analysis of coal bed methane(CBM) engineering in Hancheng. Thus，under a given condition of CBM engineering，it can be found that the absolute permeability will do higher growing and the methane production will be further improved，if the bottom-hole pressure can be controlled reasonably.

Select

NUMERICAL CALCULATION AND ANALYSIS OF DISTANCE AMONG SALT ROCK UNDERGROUND GAS STORAGE CAVERNS

LIU Jian1，SONG Juan1，ZHANG Qiangyong1，ZHANG Wenqian1，JIA Chao1，

2011, 30 (S2): -3420
Full Text:

[PDF 0 KB] (780)

+

Show Abstract

Reasonable distance between caverns is indispensable for the safety and normal operation of underground storage caverns. Many factors such as complex geological and operation conditions，high variability and stochastic behavior of material parameters influence the safety of caverns. In this paper，taking account of stability and sealability，Mohr-Coulomb criterion and damage-dilatancy criterion are used as main failure criterion. Then distributions of plastic area and damage-dilatancy area under different conditions under different distances between gas storage caverns and operating pressures are calculated by a two-gas storage cavern numerical calculation model. Failure probabilities of elements nearby the caverns are also calculated by response surface method combining with Monte-Carlo method. The calculation results indicate that：at normal operation conditions，plastic area and failure probabilities of elements nearby the caverns increase obviously with the decreasing distance between storage caverns. At the same time，damage-dilatancy area increases remarkably with the decreasing distance between storage caverns；the damage-dilatancy area even connects the two caverns when operation pressure is low. When operation pressures of two caverns are different，the influence of differential pressure on failure probabilities of elements nearby the caverns diminishes gradually with the increasing distance between storage caverns. According to the calculation results of stability and sealability，taking two times of cavern diameter as the minimum distance between gas storage caverns is reasonable.

Select

THREE-DIMENSIONAL FRACTURE NETWORK SIMULATION IN HUANGDAO WATER SEALED CAVERNS AREA

MA Feng1，BAI Fenghuai2，CHEN Gang3，LIN Wenjing1，WANG Guiling1

2011, 30 (S2): -3427
Full Text:

[PDF 0 KB] (778)

+

Show Abstract

Low permeability fractured rock is the best choice for the construction of water sealed underground oil tank. Three-dimensional fracture network simulation is an effective technical means of clarifying the essence of fracture distribution characteristics and seepage of fracture water rules for the underground project. The latest software discrete fracture network(DFN) is used to analyze the permeability of Huangdao water sealed underground oil tank based on the statistical work of field surface cracks and drilling image fracture results. Transmissibility distribution and connected compartmentalization of ZK13 are simulated in the model and the results are conceived to be reasonable and reliable through the comparison with the field test results. The example shows that the simulation results can deeply reveal the nature of fissure water seepage and could provide reference for the subsequent evaluation of water sealed effect and water inflow quantity.

Select

COMPREHENSIVE ANALYSIS OF DEFORMATION AND DESTROY OF WEAK ROADWAY SURROUNDING ROCK

ZHANG Jie1，2

2011, 30 (S2): -3433
Full Text:

[PDF 0 KB] (686)

+

Show Abstract

According to the serious problem of deformation and destroy of weak mining roadway，rock structure and mechanical parameters and ingredient and field monitoring for deformation and destroy of roadway are proceeded. The physical experiment indicates that the roof and floor belong to weak of roadway surrounding rock instability rock mass，the reliability of bolt and bolt strength is depression and difficult to form stability and effective load bearing structure because the endogenic fracture and structural fracture of coal are development. The monitoring analysis indicates that the rock mass deformation is very big，floor protrude is very serious，the now support way can?t meet the requirement of rock mass nonlinearity and big deformation character，it must lead to support lose efficacy. Based on experiment and field monitoring，the measures for controlling deformation through comprehensive reinforcement are raised，the achievement attain significant application effect.

Select

ANALYSIS ON FAILURE CHARACTERISTICS OF SHIELD TUNNEL UNDER ACCIDENTALLY INTERNAL EXPLOSION LOADING

WU Yubin1，TIAN Zhimin1，2，LUO Qifeng3

2011, 30 (S2): -3442
Full Text:

[PDF 0 KB] (714)

+

Show Abstract

In order to meet the needs of design of prefabricated assembly shield tunnel under explosion，A three- dimensional FEM model for analysis of dynamic response of shield tunnel under internal explosion loading is proposed，which can model the contact effects of segment-segment，segment-bolt and segment-soil. Taking typical metro running shield tunnel as an example，the failure mechanism and dynamic characteristics of the tunnel under internal explosion loading are analyzed. Comparison study of the blast-resistant characteristics between shield tunnel and integral cast in-situ tunnel is conducted，the failure characteristics of segment and bolt are revealed based on calculation results. Example analysis results show that blast-resistant characteristics of shield tunnel is inferior to that of integral cast in-situ tunnel，segment joint is the frail part of shield tunnel to resist internal explosion loading and enhancing bolt strength and tenacity can improve the blast-resistant characteristics of shield tunnel.

Select

REINFORCEMENT CONSTRUCTION AND MONITORING ANALYSIS OF ARCH SPRINGING COLLAPSE OF TUNNEL

HAN Tongchun1，HUANG Fuming1，ZHENG Junqing1，ZHU Jiancai2，LIN Tinsong2

2011, 30 (S2): -3449
Full Text:

[PDF 0 KB] (844)

+

Show Abstract

Construction process of mountain tunnel often encounters tunnel collapse，and collapse of arch springing has characteristics of large destructiveness and difficult detection，which is often neglected in actual project. In the Gaobao tunnel of Yongning express way，arch springing collapsed during construction. The cause of arch springing collapse and its reinforcement measure are studied. The displacement and stress of tunnel section near collapsed zone and collapsed zone after reinforcement are monitored to make sure that the surrounding rock is stable and the construction process is safe. The results show that：consolidation measure of arch springing is practicable，surrounding rock deformation and stress are well controlled，ductile injecting method is good. In the construction of tunnel making up of sand soil，much attention should be paid to the accidents caused by expansion of surrounding rock induced by rising up of ground water and rainfall infiltration. When accident of arch spring collapse occurs，surrounding rock of collapsed zone should be sealed up as quickly as possible，and surrounding rock within limits near collapsed zone should be reinforced. Excavation method of one side-surrounding pilot tunnel with short-line short-dig should be applied after monitoring result being stable near collapsed zone. The experience and conclusions presented can provide reference to design，construction and monitoring research of similar tunnels.

Select

STUDY OF PROCESS DESIGN METHOD OF LARGE CROSS-SECTION ROAD TUNNEL

ZHU Hehua1，QU Haifeng2，CAI Yongchang1，HUANG Feng1

2011, 30 (S2): -3456
Full Text:

[PDF 0 KB] (853)

+

Show Abstract

Process design method(PDM) of road tunnel with large cross-section is introduced according to the in-situ test study and finite element method(FEM) numerical simulation analysis of road tunnels in Longtoushan and Lanfeng，while the correlative practical mode is built subsequently. PDM is established based on the load-structure design method，and the loose load zone is defined by maximum tension strain of surrounding rock. PDM emphasizes more consideration about effect of a tunnel construction process，which is very different from both traditional road tunnel design codes and Протодъякнов?s(PUSI) theory. PDM optimizes the comparatively conservative support parameters by common design method，at the same time，of course can ensure the tunnel be at a whole safe state. Two engineering applications with different construction methods：double and single side-wall drift pilot excavations are studied，and the results show that PDM is more credible and practical than usual state one，and is better fit for the in-situ construction of tunnels with large cross-section. The results from this paper are in favor of advancing more efficient and reasonable design method of road tunnel with large cross-section，as well as to promote the current design level.

Select

EFFECTS OF PORE PRESSURE ON ROCK STRENGTH PROPERTIES

LIU Xiangjun，SHEN Jiankun，LIANG Lixi，HAN Lin，LIU Hong

2011, 30 (S2): -3463
Full Text:

[PDF 0 KB] (983)

+

Show Abstract

Oil/gas produced from reservoir formation will inevitably change its pore pressure，and then affect its rock mechanical properties. Strength properties of rock under different pore pressures and deformation properties of rock under periodic pore pressure are studied by triaxial compression tests in this paper. The results show that when confining pressure keeps constant，triaxial compressive strength，elastic modulus，volumetric modulus and shear modulus all present increasing trend with the decrease of pore pressure，while the Poisson ratio presents total decreasing trend. For the reservoir developed by blowdown recovery，with the decrease of pore pressure，volumetric modulus increases and volumetric compressibility decreases，rock compressibility gradually weakens. During the periodic loading and unloading process of pore pressure，axial strain，radial strain and volumetric strain will all gradually accumulate with the loop cycle，and change greatly in the initial loading and unloading，gradually tend to be stable with the increasing cycle numbers. The variation in rock strength and deformation with pore pressure shows that the drop of pressure in the early development of the reservoir has a serious impact and injury to the reservoir properties. If effective measures are never taken to stabilize the formation pressure in the early，substituted by injecting fluid in the later reservoir development period to change the formation permeability，it won?t take apparent effect. Moreover，the grand total of rock deformation may induce formation damage and even catastrophic events.

Select

ANALYSIS OF STABILITY OF SLURRY TRENCH SIDES OF DIAPHRAGM WALL BASED ON CONSTRUCTION PARAMETERS

XU Yonggang，WEI Zilong，ZHOU Guannan，SUN Yuyong

2011, 30 (S2): -3470
Full Text:

[PDF 0 KB] (835)

+

Show Abstract

Based on the diaphragm wall construction of two open-cut metro stations，we study the influence factors of stability of slurry trench sides during diaphragm wall building in soft soil by analyzing the fullness coefficient of slurry trenches corresponding to different controlling parameters. This paper also makes an analysis of distortion position of slurry trench sides by combining ultrasonic test records with concrete rising rate of diaphragm wall in the process of concreting. The analytic result shows that the rates of trench construction and perfusion have impact on the stability of slurry trench sides，yet the construction sequence and the groove depth have little effect on the stability of slurry trench sides if both the quality and the level height of slurry meet the design requirements. The deformation of slurry trench sides mainly happens within the region of 5 m below the guide wall and in the silt sand with clayey soil.

Select

ANALYSIS OF ENGINEERING PROJECTS OF RISK CONTROL IN HANGZHOU QING-CHUN ROAD CROSS-RIVER TUNNEL CONSTRUCTION

ZHANG Zhongmiao1，LIN Cungang1，WU Shiming2，LI Zongliang2，XIE Wenbin3，WANG Chengshan3

2011, 30 (S2): -3480
Full Text:

[PDF 0 KB] (711)

+

Show Abstract

Engineering projects of risk control in construction of Hangzhou Qingchun road cross-river tunnel are introduced. Contents include：causes of water leakage at the tunnel portal and soil collapse at the reinforced area when the shield setting out are put forward，moreover，avoidance and treatment measures are described. Reasons leading to the differences of settlements of the levee when two shields traversing it respectively are analyzed，and some construction measures for slurry shield to cross the levee are proposed. Reasons to the invalidation of the tail seal are studied，and techniques to shut off the groundwater using liquid nitrogen freezing method and repair the tail seal brushes in the artesian aquifer are presented. Engineering practices show that good tightness of the tunnel portal can avoid water leakage and soil collapse at the reinforced area，and optimization of parameters of shield driving can reduce disturbance to the levee while shield tunneling. On the contrary，sustainable rainfall and severe fluctuation of the chamber pressure lead to larger settlements. It is also shown that liquid nitrogen freezing method can seal off the groundwater safely and the repair of the tail seal brushes eliminates the risk of mud leakage of the shield tail successfully. These results would provide a scientific reference for risk control in similar shield tunnelling in practice.

Select

STUDY OF HYDROPOWER SLOPE ROCKMASS STABILITY CLASSIFICATION SYSTEM

ZHANG Julian1，SHEN Mingrong1，2

2011, 30 (S2): -3490
Full Text:

[PDF 0 KB] (814)

+

Show Abstract

Most slope rockmass rating originated or amended from rockmass classification designed for underground engineering，those classification systems don?t take into account the influence of failure-mechanism differences on slopes. To make up this theoretical defects of slope rockmass classification，this paper presents a rockmass classification based on slope failure mechanism. In this study，hydropower slopes were used as samples for the establishment of this classification system；eight impact factors for potential planar or already plane failed slopes were analyzed and collected，these factors are the slope geometry，the intact rock strength，the rockmass integrity features，the discontinuities characteristics，the geometrical relationship between discontinuities and slope，the engineering environment，the climate conditions and the failure history；then the multiple linear regression method was used to explore the relationship between the slope rockmass stability and the impact factors，the weights of each factor was obtained hereafter；and finally，the slope rockmass stability classification (SRSC) system was established by eliminating the factors whose weights were almost zero. Compared with the existing slope rockmass rating(SMR，CSMR) system，SRSC system?s evaluation results are closer to the experience scores which based on field condition，standard error is smaller，and evaluation accuracy rate is larger；moreover，twelve hydropower slopes were used to verify SRSC?s accuracy and applicability，correctness rate of evaluation is 100%，which indicates excellent evaluation results of SRSC system. Thus SRSC system based on slope failure mechanism is a superior rockmass classification system for slopes.

Select

DISCUSS ON FAILURE MECHANISM AND GEOLOGIC CHARACTERISTIC OF WOQIAN LANDSLIDE TRIGGERED BY WENCHUAN EARTHQUAKE

TANG Minggao，XU Qiang，ZHANG Wei，DONG Xiujun

2011, 30 (S2): -3502
Full Text:

[PDF 0 KB] (1067)

+

Show Abstract

In order to find out the characteristics of Woqian landslide triggered by Wenchuan earthquake and discuss the instability mechanism of the landslide，the author has investigated the landslide area many times. The investigation results show as follows：(1) The geologic structure of Woqian landslide is up hardness and down softness，and up steep and down slow，belongs to a kind of landslide with pattern of rips-tend towards slide. (2) Woqian landslide is an intense start-up and long run-out landslide triggered by Shikan fault movement，and its hanging-wall effect，energy convergence release effect，long time and repeat effect of earthquake wave，zoom in effect of terrain，level acceleration effect. (3) Woqian landslide behaves a series of movement and accumulation characteristics differing from landslide by gravity，for example landslide cliff of high and coarse，centrifugal super high in curve，throw to side，classify accumulation，come into being 5 areas，i.e. landslide source，steep accelerate segment，sturzstroms，accumulation and side throw. (4) Woqian landslide comes through four stages，i.e. slope shake fissure，high speed canker，sturzstrom and accumulation. The peak velocity is 56.1 m/s when sliding distance is about 800 m. The whole moving time is 57.1 s，and the average velocity is 35.6m/s in the sliding process. High potential energy and fluidization is the main reason for Woqian long run-out landslide.

Select

RESEARCH ON RELATIONSHIP BETWEEN FAULT MOVEMENT AND LARGE-SCALE LANDSLIDE IN INTENSIVE EARTHQUAKE REGION

ZHANG Yongshuang1，2，SU Shengrui3，WU Shuren1，2，SHI Jusong1，2，SUN Ping1，2，

2011, 30 (S2): -3513
Full Text:

[PDF 0 KB] (909)

+

Show Abstract

The relationship between active fault zone and large-scale landslides is a major issue on which people always concern. Based on field investigation of active fault zones and large-scale landslides induced by Wenchuan Ms 8.0 earthquake，the geological setting for large-scale landslides initiation in the Longmenshan active fault zones is documented，and the characteristics of distribution，shape，initiation and segmentation，as well as their influential factors，are summarized. Taking the Xiejiadianzi landslide-debris flow near the central Longmenshan fault zone as an example，simulations of the processes of landslide starting and fast slipping have been carried out by the discrete element method(DEM). It is thought that the disaster result of a rapid and long run-out landslide are dominated by the starting style，debris flying route and dumpling features. This research provides important information for the realization of the relationship between the fault movement and the formation of large-scale landslides，as well as prediction of the disaster result caused by earthquake landslides.

Select

RESEARCH ON SEISMIC RESPONSE ANALYSIS OF SLOPES IN NUCLEAR POWER PLANT

ZHENG Wentang1，2，CHENG Xiaojiu1，LEE C F2，FU Wenxi3，ZHOU Jiawen3

2011, 30 (S2): -3521
Full Text:

[PDF 0 KB] (750)

+

Show Abstract

The large and complicate slopes in nuclear power plants are simplified into cylinder model and slope model with free surfaces and structural planes，then the pretreatment and input of seismic wave，setting of dynamic artificial boundaries are studied. The seismic spread，reflection，oscillation and attenuation of designed simple harmonic wave and macroseism wave are simulated and verified by dynamic theory solution. Finally，the dynamic response of slope under macroseism wave is discussed by time-history dynamic analysis. The results showed that：The seismic wave has amplification effect and reflection on the free surface of slope，the weak structural plane leads to the reflection and transmission of the seismic wave. Constraint boundary gives rise to the reflection，while viscous absorption boundary and free-field boundary eliminate the reflection. The seismic wave would come into being several reflections on the slope face，and the amplification factor increases with the increasing elevation. The amplification effect of free surface of anisotropic slope is more intense than that of isotropic slope，which increases obviously on the weak structural plane. The relative slip and permanent deformation of anisotropic slope is greater than that of isotropic slope. Anisotropic condition is detrimental to the seismic stability of slope.

Select

STUDY OF DYNAMIC RESPONSE OF BEDDING ROCK SLOPE UNDER EARTHQUAKE AND INFLUENCE OF GROUND MOTION PARAMETERS

YAN Zhixin1，2，ZHANG Sen1，2，ZHANG Xuedong1，2，ZHANG Liuping1，2

2011, 30 (S2): -3528
Full Text:

[PDF 0 KB] (737)

+

Show Abstract

A model of bedding rock slope is established using FLAC2D program，and the dynamic response laws and the influence of parameters of ground motion on the dynamic responses under earthquake action are analyzed. It is shown that the structural surface plays a main control role on the failure of bedding rock slopes，displacement mainly takes place in the rock mass which on the potential sliding surface. The seismic waves are amplified by the vertical direction and free face of the slopes；and the filter function of bedding rock slope is not as apparent as soil slope. Different rock formations produce a significant amplification at certain frequency. The amplification coefficients of acceleration below the crest of slope decrease when the amplitudes and frequencies of seismic waves increase. The phenomenon is obvious in rock mass with relatively low intensity，but the dynamic response of slope becomes serious. The amplification coefficients of acceleration are less affected by the duration，while the duration has a great influence on the shear strain increment. The maximum displacement of the slope evidently increases with the increasing amplitudes and duration of earthquakes ground motion，while the maximum displacement of the slope decreases with the increase of predominant frequencies. It is approved that the failure of slope under earthquake action consists of the tension failure in the upper part and the shear failure in the lower part. The study results are helpful to further researches on the mechanism of slope instability under earthquakes action.

Select

SIMULATION OF RETROGRESSIVE LANDSLIDE FAILURE PROCESS BY STRENGTH REDUCTION FEM

CAI Wen1，CAO Hong2，LUO Yan3，LUO Guanyong2

2011, 30 (S2): -3533
Full Text:

[PDF 0 KB] (867)

+

Show Abstract

The retrogressive failure process of the slope，which has the characteristics of steps failing from slope toe towards slope crest，is simulated by several rounds of calculation in strength reduction finite element method (FEM). During simulation process，strength reduction factor is determined by dichotomy method for each calculation round. Weight of the locally failed soil is converted into slope surface load based on the static equilibrium assumption. The gradually becoming smaller reduction factor in the successive calculation rounds is adopted as the control criterion to determine whether it is a retrogressive landslide. Left abutment landslide of Jinjiang reservoir is taked as engineering example. The simulation results，which is basically in accordance with actual situations，prove that the simulation method is a feasible method.

Select

REPLACEMENT THICKNESS AND DYNAMIC STABILITY OF CUTTING BED UNDER BALLASTLESS TRACK OF HIGH-SPEED RAILWAY

LIU Xiaohong1，YANG Guolin2，FANG Wei2

2011, 30 (S2): -3538
Full Text:

[PDF 0 KB] (810)

+

Show Abstract

In view of the replacement thickness of red clay cutting bed under ballastless track of Wuhan—Guangzhou high-speed railway，based on results of indoor dynamic test and on-site dynamic response test，the dynamic stability of red clay cutting bed under ballastless track of Wuhan—Guangzhou high-speed railway is preliminary evaluated by methods of critical dynamic stress and dynamic shear strain respectively；and the theory values of minimal replacement thickness of cutting bed are given to meet synchronously two requirements of dynamic strength and dynamic deformation. After considering of railway bed structure request，actual cutting bed dynamic response influencing depth，special engineering properties of red clay and safety storage and so on，the suggestion values applied conveniently in engineering corresponding the theory values of minimal replacement thickness are also given. Influences are discussed for water content ratio and confining pressure to replacement thickness of cutting bed，the values of it increase with water ratio increases and reduce with confining pressures increase. The comparitive analysis shows that the dynamic strength condition of roadbed under ballastless track of high-speed railway can be certainly satisfied if the dynamic deformation condition of it can be done；dynamic deformation is the controlling factor of ballastless track roadbed of high-speed railway；the method of dynamic shear strain is superior to the way of critical dynamic stress. The results provide new thought for ensuring replacement thickness of roadbed under ballastless track of high-speed railway.

Select

ENGINEERING GEOLOGICAL CHARACTERISTICS OF ZHAIZICUN GIANT ANCIENT LANDSLIDE ALONG JINSHA RIVER AND ITS OCCURRENCE MECHANISMS

XU Zemin1，2，LIU Wenlian3，HUANG Runqiu2

2011, 30 (S2): -3550
Full Text:

[PDF 0 KB] (922)

+

Show Abstract

Height difference between the crown and the toe of rupture surface of Zhaizicun landslide in Jinsha river is 638 m，with about 2.5×108 m3 total rock displaced. The width of crown cracks surrounding the main scarp，which is limestone cliffs with a height of 5–30 m，is 30–100 cm. Slip source area with gullies is covered by colluvial deposit with vegetation，talus and separate giant rock blocks with a diameter of 1–6 m. The landslide occurred in Chenghai fault zone，which developed in the limestone dating to C2+3；and the landslide deposit is mainly made of cataclastic limestone and karst breccia. The Zhaizicun landslide once dammed Jinsha river and the crest of the residual landslide dam with a volume of 180 × 104 m3 opposite slip source area is 118 m high above the river. The relic landslide dam is mainly composed of 70% of limestone block with a diameter of less than 30 cm and 30% of blocks of limestone and karst breccia with a diameter of more than 30 cm. Chenghai fault zone with a length of 200 km is normal and lithospheric fault and its long-term activities make the quality of the rockmass in fault zone decrease. The undercutting of the Jinsha River flowing along the left side of the fault zone make the right bank slope increasingly steep and laid the foundation for the bank slope failure on a large scale. Chenghai fault zone is an activity fracture and the earthquake caused by its own activities is the inducing factor of Zhaizicun landslide.

Select

NEW PLASTIC SOLUTION FOR DISPLACEMENT OF ROCK TUNNELS

ZHANG Changguang1，XU Fei2，ZHANG Qinghe3，4，ZHANG Zhenguang2

2011, 30 (S2): -3556
Full Text:

[PDF 0 KB] (709)

+

Show Abstract

Based on the unified strength theory and the elastic-brittle-plastic model，the new plastic solution for displacement of deep circular tunnels in rock is deduced. The influence of the elastic modulus variation in the plastic zone，intermediate principal stress，rock softening and shear dilation is all involved in this new formula. The new displacement solution obtained in this paper has a broadly theoretical meaning. More reasonable choices could be made according to the actual engineering situations. By analyzing an engineering case，the tunnel displacement calculated with the radius-dependent Young?s modulus is between the upper and lower bounds，which reflects the distance changes of the tunnel excavation unloading affect and is more consistent with the true situation of tunnel deformation. The effects of the unified strength theory parameter and shear dilation characteristic parameter on the tunnel displacement in the plastic zone are discussed. It is shown that the intermediate principal stress，shear dilation and the elastic modulus in the plastic zone have a significant effect on the tunnel plastic displacement，in which these three aspects influence each other and work together.

Select

RESEARCH ON STRESS AND DEFORMATION MECHANISMS OF SHALLOW SECTION WITH UNSYMMETRICAL LOADING OF MULTI-ARCH TUNNEL

PAN Long1，WANG Jianguo1，CHEN Luwang2

2011, 30 (S2): -3566
Full Text:

[PDF 0 KB] (697)

+

Show Abstract

Taking Shuanghekou tunnel of Anjing expressway as engineering background，focused on the shallow section with unsymmetrical loading of multi-arch tunnel，the stress distribution of wall-rock is discussed under the combined effect of geostress and slope sliding. In order to meet the need of practice，a nonlinear method has been proposed to decompose the monitoring data；and the function between the stress and the deformation of wall-rock is established. At the same time，the remaining fluctuations is used to analyze the abnormal phenomenon in construction. The results show that when the shallow section with unsymmetrical loading of multi-arch tunnel is in the combination action of overlying load and sliding slope，the wall-rock and supporting structure，which are located in the tail of the most dangerous sliding surface，will have the largest deformation under mixed loading of tension and shearing. It is more obviously explained by monitoring data tendency item when eliminating construction and other influencing factor. Thus，the slope sliding must be taken into account when the tunnel goes through the wall-rock close to the most dangerous sliding surface.

Select

ANALYTIC SOLUTION FOR SEEPAGE FIELD OF SUBSEA TUNNEL AND ITS APPLICATION

DU Chaowei1，2，WANG Mengshu1，TAN Zhongsheng1

2011, 30 (S2): -3573
Full Text:

[PDF 0 KB] (798)

+

Show Abstract

Based on complex function and groundwater hydraulics theory，the analytic solution for seepage field of subsea tunnels，which is made up of surrounding rock，grouting circle and lining concrete，has been deduced. Using the F4 entire strong weathering bursa of Xiamen subsea tunnel as engineering background，the influences of seepage parameters of surrounding rock，grouting circle and lining on water pressure on primary support and seepage discharge are studied. The study results indicate that the construction qualities of grouting circle and primary support have great influence on seepage discharge and water pressure on primary support，so the constructions of grouting circle and primary supporting should be emphasized. In case of the blocked drainage system and the decreasing seepage discharge，the water pressure on the primary and second support will be redistributed. Considering the theoretical analysis result and the data by real time monitoring of water pressure on site comprehensively，it is put forward that in the circumstance of limit drainage，the water pressure behind the primary support can be reduced to 1/3 of the full hydrostatic pore pressure.

Select

STUDY OF GROUND TREATMENT OF DREDGER FILL IN-SITU TEST WITH STALK CUSHION USING VACUUM PRELOADING METHOD

WU Yajun1，ZOU Daomin1，TANG Junwu2，LIU Wei2

2011, 30 (S2): -3583
Full Text:

[PDF 0 KB] (686)

+

Show Abstract

For the very soft dredger fill site，it seems very hard for workers and construction machine standing and moving on the ground surface. That site is intended to be in use for agriculture. To meet such a need，the ground improvement should be implemented. Due to lack of the resources of sands，the sand cushion commonly used in the conventional method is replaced by reeds acted as drains in the vacuum preloading tests. Comparisons between results of vacuum preloading tests with and without bedding layer are obtained. Due to different loading processes of vacuum preloading tests with and without bedding layer，effects of consolidations of foundation vary considerably. In the case with no reed bedding layer，the velocity of consolidation in early stage is faster with small foundation settlement and low time cost，but this velocity decreases faster with the reduction in the settlement of the ground. In another case with reed bedding layer，the velocity of consolidation in early stage is relatively slow with some decreasing rate. It lasts about 33 d to make the same settlement magnitude as the site with no the reed cushion，and makes more 10.4% of total settlement than with no the reed cushion at the end. Moreover，the bearing capacity is higher than without reed layer. It shows that vacuum preloading method with reed bedding layer is a better ground treatment method. It has greater effects，shorter construction period and lower cost. It could be widely spread in the future construction.

Select

CALCULATION METHOD OF LATERAL DISPLACEMENT OF SOIL NAILING BASED ON MINDLIN SOLUTION

WEI Huanwei1，SONG Fengbo2，YANG Min3

2011, 30 (S2): -3594
Full Text:

[PDF 0 KB] (791)

+

Show Abstract

Lateral displacement of soil nail is a key parameter affecting its safety，however，the existed studies have not provided any reasonable theorical calculation method. A theorical calculation approach based on the MIDNLIN solution，in which virtual excavation stress is used to simulate the excavation status of soil nailing，is applied to obtain the lateral displacement of soil at potential failure surface and the end of nail caused by the virtual excavation stress and soil and nail shear stress. The approach has a hypothesis on the base of the in-situ measured data that the distribution of between soil and nail is double-triangle including two unknown coefficients，which can be worked out by two equations from the zero relative displacement and the equivalent axial force of soil nail at both sides of potential failure surface. Then the lateral displacement at the surface of soil nailing is the sum of the tension deformation of nail and the lateral deformation of soil at the end of nail. The measured data from French research test on soil nailing are used to illustrate the validity of the proposed calculation model.

Select

EXPERIMENTAL RESEARCH OF HYSTERESIS EFFECT OF LAND SUBSIDENCE CAUSED BY WATER RELEASING

XU Haiyang1，2，ZHOU Zhifang1，GAO Zongqi3

2011, 30 (S2): -3601
Full Text:

[PDF 0 KB] (810)

+

Show Abstract

Land subsidence caused by groundwater overpumping is becoming a serious geological disaster. Based on previous studies，testing device of land subsidence was manufactured and the saturation method of sample was improved. Land subsidence caused by water releasing was simulated by the use of this device. Hysteresis effect of land subsidence was studied on land subsidence response to changes of water level and pore water pressure in the process of land subsidence. The results show that：(1) The deformations of both confined aquifer and clay layer show lag phenomenon；(2) Under the same test conditions，the lag-time of deformation of clay layer was (going longer with the thickness of caly layer)in direct proportion to thickness of clay layer. When the test was completed，clay specimens were taken out from the bottom and top of clay layer respectively and measured by conventional consolidation test. The results indicate that the land subsidence caused by water releasing was not uniform in the vertical direction. The shorter the distance between the clay layer and the pumping aquifer is，the greater the degree of compression of the clay layer is.

Select

EXPERIMENTAL RESEARCH ON DYNAMIC SHEAR STRAIN THRESHOLD OF CUTTING BED RED CLAY UNDER BALLASTLESS TRACK OF WUHAN-GUANGZHOU HIGH-SPEED RAILWAY

LIU Xiaohong1，YANG Guolin2，FANG Wei2

2011, 30 (S2): -3610
Full Text:

[PDF 0 KB] (691)

+

Show Abstract

In view of the dynamic stability of red clay cutting bed under the ballastless track of Wuhan- Guangzhou high-speed railway，the reformed stress-controlled dynamic triaxial test instrument is utilized firstly to measure short-time and fatigue dynamic shear strain threshold，replacing the shear strain-controlled resonant column test apparatus not existing at home now. A complete set of short-time and fatigue cyclic triaxial testing program and test data processing methods are put forward，it opens up a new test way of measuring dynamic shear strain threshold. The values of short-time and fatigue dynamic shear strain threshold and its corresponding curves of red clay under 9 kinds test conditions are given. The fatigue dynamic shear strain threshold of red clay is always less than its short-time dynamic shear strain threshold，and the former is 2/10–3/10 of the latter. There are three types of curves for red clay：the stable ones，critical ones，destructive ones，and there are similar trends features in the same kind of curves under different test conditions. The influences on dynamic shear strain threshold of red clay are discussed for water content ratio and confining pressure，and the simple and practical empirical formulas of estimating dynamic shear strain threshold are provided. Based on contrastive analysis，we think it is feasible for the stress-controlled cyclic triaxial test to measure dynamic shear strain threshold replacing the shear strain-controlled resonant column test，and test results and data processing methods are correct and reasonable. The results provide valuable first-hand information for the dynamic stability evaluation of red clay subgrade of high-speed railway，as well as useful reference for similar projects.

Select

SEISMIC PASSIVE EARTH PRESSURE CALCULATION OF COHSIVELESS SOIL UNDER UNIFORM LOAD

WANG Kuihua1，MA Shaojun1，2，WU Wenbing1

2011, 30 (S2): -3617
Full Text:

[PDF 0 KB] (701)

+

Show Abstract

Based on the hypothesis of planar sliding surface，a modified pseudo-dynamic approach is proposed to overcome some shortage in method of seismic passive earth pressure calculation. The formulas are derived for the calculation of lateral earth pressure and total passive force under seismic condition by using pseudo-dynamic approach. The effects of wall friction angle，soil friction angle，horizontal and vertical seismic coefficients on the seismic passive force have been explored. The parametric study shows that the total seismic passive earth pressure increases with the increase in values of wall friction angle and soil friction angle；while it decreases with the increase in values of horizontal and vertical seismic coefficients. The calculation results of seismic passive force obtained from present analysis is larger than those obtained from Mononobe-Okabe theory. Unlike the Mononobe- Okabe theory，the present analysis predicts a nonlinear variation of passive earth pressure along the retaining wall.

Select

STUDY OF DYNAMIC LONGITUDINAL IMPEDANCE OF TAPERED PILE CONSIDERING LATERAL INERTIAL EFFECT

WU Wenbing1，2，WANG Kuihua1，2，WU Denghui1，2，MA Boning1，2

2011, 30 (S2): -3625
Full Text:

[PDF 0 KB] (915)

+

Show Abstract

Based on Rayleigh-Love rode model，the longitudinal vibration of tapered pile embedded in layered soil is theoretically investigated by considering lateral inertial effect of tapered pile. At first，considering stratification of the surrounding soil and variable cross-section of the tapered pile，the pile-soil system is discretized into finite segments. Then，by virtue of Laplace technique and impedance function transfer method，the analytical solution of complex impedance of tapered pile under longitudinal exciting force is derived. Finally，by means of parametric study method，the influence of the design parameters of tapered pile on complex impedance at the pile head is investigated within the low frequency range，and the complex impedance of tapered pile is compared with that of uniform cross-section pile with same volume. The results show that：(1) When other design parameters of tapered pile remain unchanged，dynamic damping increases as the cone-angle increases，dynamic stiffness also increases as the cone-angle increases，but the increase magnitude decreases gradually as the frequency increases；(2) When other design parameters of tapered pile remain unchanged，dynamic stiffness decreases as the cone-angle increases，and dynamic damping increases as the cone-angle increases；(3) When the volume and length of tapered pile are the same as that of uniform cross-section pile，dynamic stiffness decreases as the cone-angle increases，and dynamic damping increases as the cone-angle increases. When the volume and radius at the pile tip of tapered pile are the same as that of uniform cross-section pile，dynamic stiffness increases as the cone-angle of tapered pile increases，and dynamic damping increases as the cone-angle increases within a small range of cone-angle.

Select

EFFECT STUDY OF PILE STIFFNESS ON PILE-SOIL DYNAMIC INTERACTION PROBLEM

MA Kang1，PEI Jianliang2

2011, 30 (S2): -3632
Full Text:

[PDF 0 KB] (741)

+

Show Abstract

By conducting the centrifuge dynamic tests coverage to two kinds of piles with great stiffness difference，This paper investigated that there exist some quite different characteristics between behavior of flexible and stiff piles during earthquake shakings. For the flexible piles，the bending moment drops to a very small value below the changeover point. This is similar to the bending moment distribution curves for laterally loaded piles，and suggests that，for flexible piles，the clay beneath a certain depth is able to provide lateral support for the pile. On the other hand，for the stiff piles，the bending moment changes over at a much larger depth indicating that lateral support is not effective until much deeper. There is also much larger reverse moment below the changeover depth. This is quite different from the typical moment distribution of laterally loaded piles，the surrounding clay effect on the pile mainly focus on the providing additional inertia forces. Finally，a skillful parameter of pile-raft native frequency was presented herein to quantify pile flexibility.

Select

EFFECTS OF BENDED PLASTIC DRAINAGE PLATES ON CONSOLIDATION CAUSED BY VACUUM PRELOADING

YING Shu1，CHEN Pingshan2

2011, 30 (S2): -3640
Full Text:

[PDF 0 KB] (1041)

+

Show Abstract

The practices show that the plastic drainage plates would be bended because of the large settlement of soft foundation treated by vacuum preloading，which makes the longitudinal drainage content of prefabricated vertical drains(PVDs) decreasing then impairs the improvement performance of the deeper layer soil. To decrease the influences，the scheme of twice installation of PVDs was proposed for the ultra-soft foundation，which meant that the shallow-layer soil was treated firstly then the longer PVDs would be installed to improve the whole foundation as the shallow-layer soil had certain bearing capacity. Combined with the vacuum preloading engineering in the reclamation project of Dingshan reclamation area in Wenzhou city，Zhejiang province，the longitudinal drainage content of PVDs was measured under the different bended states to estimate the variation of the vertical permeability of PVDs during the improvement. The Duncan-Chang constitutive model was developed based on the FEM program automatic dynamic incremental nonlinear analysis(ADINA)，then the permeability variation of the bended PVDs and the initial un-dissipated excess pore water pressure were considered in 3D FEM simulation. Comparing the calculated results with the field data，it showed that the settlement and reduction of pore pressure caused by twice installation of PVDs were more than that caused by once installation of PVDs，and the calculated results were more approximate to the field data when considering the influence of the bended PVDs. The conclusions can be useful for the design and construction of the similar engineering.

Select

PRELIMINARY STUDY OF RELATIONSHIP BETWEEN SHALLOW SOIL REINFORCEMENT AND FRACTAL CHARACTERISTICS OF VEGETATION ROOTS IN BIOTECHNICAL SLOPE PROTECTION

XIA Zhenyao1，2，ZHOU Zhengjun2，HUANG Xiaole2，XU Wennian1，2

2011, 30 (S2): -3647
Full Text:

[PDF 0 KB] (737)

+

Show Abstract

In biotechnical slope protection engineering，the spatial distribution of plant roots exerts an important impact on the strength of root-soil reinforced composite. Two common plants，i.e. medicago sativa and cynodon dactylon，were planted in containers. Till the roots penetrating the whole soil (referring to base material of vegetation-growing concrete)，direct shear tests along the soil depth on the undisturbed soil and root-soil composite system are conducted respectively，and the fractal characteristics of roots are analyzed. The relationship between cohesive strength added value and the fractal characteristics of vegetation roots is to be studied by contrast. The results show that：(1) The shear strength of soil increases evidently after roots distributing in soil，especially the added value of cohesive strength increases obviously，but the increasing amplitudes of medicago sativa and cynodon dactylon manifest very significant difference. (2) The roots of the two plants both have fractal structure，the more biomass and well-distributed of roots in soil，the fractal dimension is comparatively larger. (3) The cohesive strength added value of soil is significantly positively correlated with the fractal dimension of the vegetation roots.

Select

STUDY OF PREMATURE REFUSAL OF LARGE DIAMETER PIPE PILE CAUSED BY PILE DRIVING SUSPENDING

LI Sa1，HUANG Jianchuan1，ZHOU Yangrui2，JIANG Baofan2

2011, 30 (S2): -3656
Full Text:

[PDF 0 KB] (877)

+

Show Abstract

With the platform size increment，the large diameter pipe piles are used in practice more and more. Pile driving maybe suspended because of many reasons during installation. Whether the driving could be re-started or not is an important problem that many people concerned. In this paper，we study the change of excess pore water pressure and effective stress during continuous and discontinuous striking with dynamic FEM. Based on FEM results，the mechanics of premature refusal caused by pile driving suspending in sand layers is discussed combined with a practical case. The results of dynamic FEM present that continuous driving causes pore water pressure accumulating around the pile tip. If the pile driving suspends，the excess pore water pressure dissipate quickly to cause the effective stress changes obviously within 1–2 times of the pile diameter. The end soil resistance increase，but the change of friction is just near the vibration fountain. The measurement data of the practical case show that after 3 months suspending，the friction in sand layer recovered and exceeded initial value，especially near pile tip. The friction increment is small in the thin sand layer between two clay layers. The friction in clay layer is still lower than the initial value. When we predict soil resistance after suspending，for the friction，the effecting scale of driving and suspending time should be considered；for the end resistance，the restarting procedure is important.

Select

STUDY OF BLOCKAGE ACCIDENT OF PRE-EMBEDMENT GROUTING PIPES AND ITS CORRESPONDING TREATMENT METHOD

ZHANG Qianqing 1，2，ZHANG Zhongmiao 1，2

2011, 30 (S2): -3664
Full Text:

[PDF 0 KB] (1015)

+

Show Abstract

This paper presents an accident caused by unopened pre-embedded grouting pipes of working piles at a site of Zhejiang Province，and then proposes construction measures of post-grouting conducted using two pre-embedded grouting piles，a borehole drilled in pile shaft and a hole embedded in soil around pile. The variation of grouting pressure and grouting amount with time during different schemes of post-grouting was also discussed. In the scheme of post-grouting conducted using a borehole drilled in pile shaft，rubber packer can be used to avoid cement sully leakage，while rubber packer and swelling water-stopper can be adopted to prevent cement sully leakage，as well as intermittent grouting technique being employed，in the scheme of post-grouting conducted with a borehole embedded in soil around pile.

Select

SEEPAGE CYLINDRICAL HEAT SOURCE MODEL OF DAM AND ITS EXPERIMENTAL STUDY

DONG Haizhou1，2，ZHANG Xiaoyan2

2011, 30 (S2): -3670
Full Text:

[PDF 0 KB] (747)

+

Show Abstract

The concentrated leaking water has heat exchange with rock and soil during its flowing，resulting in the change of ambient underground temperature distribution. Considering its own characteristics，the concentrated leakage passage can be regarded as a circle column. Based on analyzing the characteristics of temperature and seepage fields influenced by concentrated leakage passage in rock and soil，a circle columnar heat source model has been established to describe the heat conduction processes in and out of the passage，respectively. By the deduction of heat conduction differential equation，the functions of fluid temperature distribution on flow path have been determined under two conditions of finite and infinite leaking pathway length，eventually leaking velocity can be determined by inverse calculation. Through laboratory experiments，the heat transfer of leaking groundwater has been simulated，and the distribution of temperature has been studied under different influences such as heat source intensity，boundary conditions，and leakage flux，etc. Comparison of the experimental data and the corresponding model value showed that the errors were very small，which proved that the established heat source model and its calculation method were practicable.

Select

STUDY OF ENGINEERING GEOLOGICAL CHARACTERISTICS OF GRAVEL PEBBLE LAYER FOR DAM FOUNDATION OF HYDROPOWER PROJECT

WANG Qiguo

2011, 30 (S2): -3680
Full Text:

[PDF 0 KB] (774)

+

Show Abstract

The gravel and pebble is a common kind of coarse-grained soil in the riverbed of hydropower project，but its engineering properties have a significant impact on the layout of the dam project while its thickness is much large. The study object is the gravel layer deposited lately in Shangjiang to Qizong river reach riverbed of Jinsha River，which is much thick. The study employs some comprehensive methods，such as exploration，grain size analysis，in-situ tests，and laboratory tests of physico-mechanical properties for imitated gradation sample，and find out that this layer has the frame from coarse grains and some geological characteristics of this layer，such as much high bearing capacity，shear resistance，modulus of deformation and elasticity，and moderate to heavy permeability. This paper discusses the engineering geological problems from different plans while using this layer or clearing it. The study result provides the geological basis for the study of building dam on the gravel layers，and there is a certain reference value for similar projects and the soil mechanics study.

Select

MULTI-SCALE DAM DEFORMATION PREDICTION BASED ON EMPIRICAL MODE DECOMPOSITION AND GENETIC ALGORITHM FOR SUPPORT VECTOR MACHINES (GA-SVM)

ZHANG Hao，XU Sifa

2011, 30 (S2): -3688
Full Text:

[PDF 0 KB] (734)

+

Show Abstract

Empirical mode decomposition algorithm is used to decompose dam deformation data. By obtaining the multi-scale deformation components，the characteristics of deformation components and their related influence factors are analyzed. According to those characteristics，the independent GA-SVM deformation component prediction models are built，used to combine construct the empirical mode decomposition based GA-SVM multi-scale deformation prediction model. By analyzing the dam deformation data from a real case with the empirical mode decomposition，the following views is proved: the empirical mode decomposition can effectively perform the multi-scale decomposition on dam deformation data；and the deformation components decomposed by empirical mode decomposition algorithm have more clear characteristics which can be easily applied to the influence factors analysis for deformation components and surely achieve an higher prediction accuracy. Since the empirical mode decomposition based on GA-SVM multi-scale deformation prediction model is composed of different deformation components of prediction models，it is capable of showing the intrinsic principles of dam deformation，and able to perform dam deformation prediction in different feature scales simultaneously. Comparing accuracies via multi-scale dam deformation prediction model and multiple regression，time series analysis，GM(1，4)，BP neural network and GA-SVM dam deformation prediction model，the empirical mode decomposition based GA-SVM multi-scale deformation prediction model is proved as a valuable new method with higher accuracy for dam deformation prediction.

Select

BACK ANALYSIS ON CONSTRUCTION AND OPERATION PROPERTIES OF SHUIBUYA CONCRETE FACE ROCKFILL DAM

ZHU Sheng1，2

2011, 30 (S2): -3695
Full Text:

[PDF 0 KB] (811)

+

Show Abstract

According to the rockfill large-scale field test results，as well as Shuibuya concrete face rockfill dam?s deformation monitoring data during the construction and water storage period，Duncan E-B model parameters and incremental rheological model parameters of rockfill back-analysis are decided by immune genetic algorithm method；the panel cavity phenomenon at construction period and the behavior of the dam at the beginning of water storage run-time were verified；the calculated results of the dam?s long-running characteristics are indicated that the dam is safe，and 200 m-grade CFRD construction technology has more and more matured. However，it paid attention to the panel extrusion phenomenon because the rheological value in dam?s upstream rockfill zone increased more evidently due to water pressure.

Select

SURFACE-BLOCK ANALYSIS OF UNDERGROUND CAVERN BASED ON 3D GEOLOGICAL MODELING

ZHONG Denghua，LU Wenyan，LIU Jie，TONG Dawei

2011, 30 (S2): -3702
Full Text:

[PDF 0 KB] (745)

+

Show Abstract

According to both determinate geological and statistical date，different categories of geological objects are built through coupling stochastic network simulation technology and 3D geological modeling，which based on a NURBS-BRep hybrid data structure，and then 3D refined model of rock structures are completed. Based on the 3D refined model，the concept and mathematical definition of surface-block are presented，comprehensive consideration of stochastic fissure and definite geological structural planes such as spatial faults and excavation face of underground structures，three theorems—sealability，completeness and uniqueness，are put forward to realize identification and analysis of surface-block. In combination of actual project，surface-blocks around underground cave are quickly identified by using surface-block identification theorems and related technologies，supplying much effective geological and geometric information for the following stability analysis and surrounding rock support.

Select

FINITE ELEMENT ANALYSIS METHOD ON BEARING CAPACITY AND PROGRESSIVE FAILURE OF REINFORCED-SAND RETAINING WALLS

PENG Fangle1，2，CAO Yanbo1

2011, 30 (S2): -3713
Full Text:

[PDF 0 KB] (759)

+

Show Abstract

In order to develop a rational numerical method for simulating the bearing capacity and progressive failure on reinforced-sand retaining walls and to gain a better insight into their associated reinforcing mechanisms，a set of model experimental results from well-controlled fully-instrumented load model tests of reinforced sand retaining wall are simulated by using of a nonlinear elasto-plastic finite element model considering strain localization. This constitutive model for sand is developed on the modified plastic strain energy concept. A strain localization parameter S is introduced in the constitutive model to describe the effect of shear banding after the peak strength of sandy element. It is found that the load-settlement relationships obtained from finite element method(FEM) analysis are generally in good agreement with those from the physical experimental results. The reinforcing mechanism and the progressive failure with developments of shear bands in reinforced sandy ground are also reasonably simulated by the proposed FEM analysis.

Select

STUDY OF STRESS AND DEFORMATION CHARACTERISTICS OF ZHANGMAO NEARLY SATURATED LOESS TUNNEL INITIAL SUPPORT OF ZHENGZHOU—XI?AN PASSENGER RAILWAY

ZHANG Aijun1，2，BAI Mingzhou1，XU Zhaoyi1，HUO Yuhua2，BAO Hairong2，LEI Jun2，DU Yanqing1

2011, 30 (S2): -3720
Full Text:

[PDF 0 KB] (717)

+

Show Abstract

Engineering properties of loess is affected obviously by moisture content. Zhangmao tunnel of Zhengzhou—Xi?an passenger railway is through nearly saturated loess with the moisture content of 20%，which is very difficult for construction. The construction geological condition of Zhangmao tunnel is analyzed and the result is made to determine the excavation method. The special excavation method is studied and a specific step of the tunnel continued excavation is given. The excavation technology needs for rapid closure of the construction cutting face. According to the tunnel design，this tunnel has a very large size excavation section. So the three-dimensional non-contact deformation observation methods are studied in order to get information fastly. The characteristics of crown settlement and the two walls convergence after the initial support of the excavation are tested in site for a long time. Combined with earth pressure cells and strain gauge testing on the surface of the initial support，the characteristics of soil pressure and surface contact force on the initial support are studied. The characteristics of deformation and stress of initial support on the condition of seven-step excavation in three steps of nearly saturated loess are obtained. The limit deformation amount characteristics of initial support of the loess tunnel under this kind of tunnel excavation method are summarized and it can be a reference for similar projects.

Select

MODEL TEST AND NUMERICAL SIMULATION OF RETAINING WALL UNDER DIFFERENT DISPLACEMENT MODES

ZHOU Jian1，2，GAO Bing1，2，PENG Shuquan1，2

2011, 30 (S2): -3727
Full Text:

[PDF 0 KB] (832)

+

Show Abstract

Combined with the size designed by prototype proportion，the model box is self-developed by using angle iron and organic glass with high strength. The water and soil pressure distributions and the micro-parameters of the shear zone behind retaining wall are tested under different displacement modes. Based on the model test，using secondary development particle flow program PFC2D ，the sand retaining wall is simulated by discrete element method. The passive failure mechanisms of the retaining wall are studied under different displacement modes. The different wall movement modes including three kinds of basic modes，i.e. translation(T)，rotation about base(RB)，rotation about top(RT) and two combinational modes，i.e. rotation about the point below base(RBT)，rotation about the point above top(RTT). Changes of lateral pressure，soil displacement field and deformation，and the particle aggregate internal shear strain rate distribution when the retaining wall reach a certain displacement are analyzed. Numerical simulation results indicate that the retaining wall of active and passive earth pressure simulation results are basically consistent with experimental test results；and the influence law of soil pressure distribution can be better reflected as the retaining wall under different displacement modes.

Select

CHARACTERISTICS OF GROUND MOTION INDUCED BY A SHORT DELAY BLASTING IN LOESS FIELD

SUN Junjie1，2，QIU Rendong3，XU Shunhua2，WANG Lanmin1，2

2011, 30 (S2): -3738
Full Text:

[PDF 0 KB] (712)

+

Show Abstract

Based on a short delay blasting executed in the typical seismic loess field of Loess Plateau，the time histories characteristics，attenuation laws and frequency spectrum features of ground motion induced by the blasting are investigated. In-situ observation data show that exploding ground motion in loess field has two essential characteristics evidently，i.e. an instantaneous large peak ground acceleration(PGA) and a shorter duration. Analysis results of exploding ground motions reveal that effective duration is the most important factors to influence design effects of a short delay blasting. Independent exploding events in the blasting process have an evident feature that the time histories could be connected each other discretionarily. As a result，the duration of exploding ground motion may be lengthened through this kind of connection work. These connection results of time histories would not influence the spectral characteristics of ground motion induced by the short delay blasting. The new time histories are better in the application of laboratory and field tests to understand the response behaviors of soils and structures. The spectral response of blasting ground motion tends to attenuate with the increase of distance between the center of exploding field and observation points，especially for the high frequency ground motion，which has a greater reduction distinctly. The H/V values of frequency spectrum，meanwhile，become greater with the observational distances increase gradually. This phenomenon figures the variation features between horizontal component and vertical component of exploding ground motion. As the exploding energy accumulates，lower frequency energy of ground motion associates with the blasting increases gradually；and the frequency spectrum features of the ground shock approach an actual seismic oscillation by degrees.

Select

RESEARCH ON PULL-OUT FRICTION TEST OF SHRUB CARAGANA KORSHINSKII ROOTS FOR SLOPE PROTECTION IN LOESS AREA OF NORTHEAST QINGHAI—TIBETAN PLATEAU

ZHANG Xingling1，HU Xiasong2，3，MAO Xiaoqing1，ZHU Haili2，LI Guorong2，CHEN Guichen4

2011, 30 (S2): -3745
Full Text:

[PDF 0 KB] (756)

+

Show Abstract

To study the relationship between shrub roots and soil friction，the shrub Caragana korshinskii is planted on the slopes of the test area in Xining basin and the test is carried out on the roots when Caragana korshinskii grew for sixteen months. The pull-out friction test for Caragana korshinskii roots are carried out by speed rate 2.67 mm/min in the vertical pressures 1.22，24.39，36.59，51.22 kN. The test results show that the root-soil friction grew with displacement of roots increasing in the soil；relationship curve between root-soil friction and displacement represents a linear relation in the initial stage of test，then represents an obvious non-linear relation with the development of the experiment；with the displacement of roots increasing in the soil，root-soil friction obviously increases，and a given degree increases；when the friction increases to a certain degree，it arrives at its peak and keeps constant，showing that at this time root-soil friction reaches to the largest and keeps balance with pull-out，with displacement of roots increasing in the soil，root-soil friction gradually decreases to a given degree，then to a steady state and a new balance. The test results also show that the root-soil friction obviously increases with the increasing vertical pressure，representing a linear relation，at the same time，the root-soil friction gradually decreases with soil moisture content increasing，representing an approximate linear relation in this experimental investigation. It is useful to further discuss the mechanism of roots reinforcement and anchorage that increase soil strength of slopes，and meanwhile，it is of theoretical significance and practice value in preventing the geological hazards that happen in shallow soil of the slopes.

Select

LARGE-SCALE SHAKING TABLE MODEL TEST STUDY OF DYNAMIC RESPONSE AND DYNAMIC FAILURE OF SUBGRADE

LI Jinbei1，ZHANG Hongru1，LI Zhiqiang2

2011, 30 (S2): -3754
Full Text:

[PDF 0 KB] (695)

+

Show Abstract

Aimed at the seismic response and damage of fill subgrade，a large-scale shaking table model test of subgrade with the scale of 1：20 is introduced. The model subgrade is built by soil with a height of 1.93 m，length of 3.0 m and thickness of 1.4 m. A series of tests were performed with different kinds input seismic waves，amplitudes and frequencies. The dynamic responses of subgrade under earthquake，weak of portions，failure modes，as well as the influence of ground motion parameters are discussed. Results show that the subgrade has amplification effect to input seismic waves，and the effect become extremely prominent around the crest of the subgrade and the top of the retaining wall. The study also show that the top of the retaining wall and the crest of the subgrade are the vulnerable parts of subgrade and cracks normally appear near these parts under seismic motion. The amplification coefficients of the peak acceleration along subgrade slope surface decrease with the increasing earthquake amplitudes. The soil in subgrade has amplification effect to input seismic waves at high frequency and filtering effect at low frequency；and the filtering effect becomes more prominent with the increase of earthquake amplitudes. Lots of cracked locations are identified under gradually increased seismic. Vulnerable parts of the subgrade to earthquake loading and various factors that affect the earthquake-resistant behavior of the subgrade，such as the frequencies of waves，are discussed under seismic motions of different levels. The results are helpful to reveal the mechanism of subgrade damage under earthquake，and provide references for aseismic design of subgrade engineering.

Select

THE INFLUENCE OF WATER CONTENT ON UPLIFT ULTIMATE CAPACITY OF ENLARGED BASE PILES IN UNSATURATED SILT

KONG Linggang1，2，ZHANG Geqiang1，2，CHEN Renpeng1，2，CHEN Yunmin1，2，XING Yuelong3，YING Jianguo3

2011, 30 (S2): -3762
Full Text:

[PDF 0 KB] (775)

+

Show Abstract

To evaluate the uplift behavior of enlarged base piles，a simplified numerical model for the piles in silt has been developed in this study and its calculated results are compared to the results of large-scale model tests. Agreement between the calculated results and the test results is excellent. A series of numerical analysis were then performed to investigate the effects of raining and ground water level on the uplift capacities of enlarged base piles with different depths. It is found that raining has a more significant influence on uplift capacities of the enlarged base piles with shallow embedment，while the variation of ground water level has a significant influence on the enlarged base piles with different depths.

Select

ARCHING MONITORING AND ANALYSIS OF GRAVELLY SOIL COREWALL IN PUBUGOU DAM DURING CONSTRUCTION PERIOD

CHEN Xianghao1，DENG Jianhui1，LI Peng2，KE Hu3

2011, 30 (S2): -3770
Full Text:

[PDF 0 KB] (768)

+

Show Abstract

Excessive arching existing in the high rockfill dam corewall during construction period，is inclined to produce the hydraulic fracturing and concentrated leakage consequently during the storage period. Therefore，the analysis and evaluation of the arching characteristics of high corewall rockfill dam during construction period，is of high-guiding significance to the progress of following storage and the consequently construction of higher rockfill dam corewall in domestic. Based on the stress monitoring data of gravelly soil corewall in Pubugou dam during construction period，and combined with the practical deformation monitoring data，using the actual construction process and field building procedure，the arching in gravelly soil corewall have been analyzed during construction period in time and space scale respectively. Analysis found that：arching during construction period is gradually shown with the accompany of the construction and consolidation progress. With the increasing of dam height and the passing of time，the arching is more and move obvious. The strongest arching of corewall occurs in the 1/3 height of dam. Except the vicinity of contact surface between core and shell，the place near the dam axis also have strong arching. To reduce the arching during construction period，the upstream and downstream dam shell should always being watered，and the height of corewall should be kept slightly higher than the dam shell，and the valley higher than the slope.

Select

STUDY OF TEMPERATURE AND CONFINING PRESSURE EFFECTS ON POROSITY AND PERMEABILITY IN LOW PERMEABILITY SANDSTONE

LIU Xiangjun，GAO Han，LIANG Lixi

2011, 30 (S2): -3778
Full Text:

[PDF 0 KB] (779)

+

Show Abstract

Porosity and permeability are two key parameters of reservoir rocks which have been noticed widely for their measuring conditions and methods. The effects of confining pressure and temperature on porosity and permeability are studied through two groups of low permeability sand rock samples. Under the conditions of confining pressure 5 MPa and temperature 25 ℃，porosity of the first group of sand rock sample ranges from 3.2% to 4.6%，permeability from 0.098 8×10－3 μm2 to 0.191 9×10－3 μm2. And the second one?s porosity ranges from 12.8% to 14.2%，permeability from 0.176 7×10－3 μm2 to 0.301 3×10－3 μm2. The first group sandstone rock samples from subsurface formation and the second group from outcrop formation. Experimental temperature ranges from 25 ℃(room temperature) to 80 ℃ and confining pressure varies from 5 MPa to 55 MPa. Results show that porosity and permeability are strongly sensitive to confining pressure from 5 MPa to 55 MPa and temperature from 25 ℃ to 80 ℃. Both porosity and permeability decrease with confining pressure or temperature increase. Pressure effect on permeability is much higher than temperature. Generally，temperature effect on porosity is a little higher than pressure. Keeping confining pressure constant 5 MPa，increasing temperature from 25 ℃ to 80 ℃，porosity and permeability of the first group sandstone samples decrease 34.7% and 75.1% respectively；the second group's porosity and permeability decrease 18.4% and 35.2% respectively. Keeping temperature constant 25 ℃，increasing confining pressure from 5 MPa to 55 MPa，porosity and permeability of sandstone with low porosity and low permeability decrease 32.3% and 89.5% respectively；high porosity and low permeability sandstone porosity and permeability decrease 4.6% and 77.4% respectively.

Select

NUMERICAL FORMAT OF SPATIALLY MOBILIZED PLANE CRITERION AND ITS REALIZATION IN FLAC3D

LI Tao1，LIAO Hongjian1，XIE Yongli2

2011, 30 (S2): -3785
Full Text:

[PDF 0 KB] (832)

+

Show Abstract

The numerical format in FLAC3D of spatially mobilized plane(SMP) criterion was derived and the plasticity factor λs is obtained by solving a cubic equation. Then the SMP criterion is imported into FLAC3D on the secondary development platform provided by the software using a dll document developed by C++. The feasibility of the dll document was certified by the comparison between numerical and analytical results of true triaxial numerical test，thick-walled cylinder problem and slope stability analysis. Slope stability analysis indicates that the slope failure processes are similar calculated by M-C and SMP criterion. The factor of safety calculated by SMP criterion is bigger than M-C and the plastic zone and displacement calculated by SMP is smaller than M-C using the same reduction factor because SMP criterion can consider the influence of intermediate principal stress on the yield surface.

Select

STUDY OF VOID MODEL FOR FLUID FLOW THROUGH ROUGH JOINT BY CONSIDERING 3D TOPOGRAPHY CHARACTERISTICS

XIAO Weimin1，2，XIA Caichu1，2，WANG Wei3

2011, 30 (S2): -3795
Full Text:

[PDF 0 KB] (784)

+

Show Abstract

Joints are the main passages for underground water flowing through rock-masses. Fluid flow through joint has been one of research focuses on joint hydraulic properties. Due to the joint surface is rough and uneven，flow through a rough joint is greatly different from that between a pair of parallel plates. A void model for fluid flow through a rough rock joint is established. The joint plane is divided into a series of square meshes with the dimension of 1 mm×1 mm，the apertures of the grids of each mesh are determined by the 3D void composite topography. Assumed that the cubic law is applicable for fluid flow analysis in each mesh，analyse are performed one mesh by one mesh. Fluid flow through the whole joint plane is calculated by considering the continuity equation among the meshes and a procedure for flow calculation was compiled by MATLAB functions. Then an artificial marble tensile fracture is taken as an object，different contact states are formed by offsetting the upper joint surface along the length direction from the lower one for 1，2，3，4，5 and 6 mm respectively. The 3D void composite topographies in these six cases are calculated by contact algorithm，thus obtaining joint aperture distributions and the mean apertures under different contact states. The theoretical volumetric flow rates under different contact states calculated by void model and cubic law are compared with the results of laboratory flow tests carried out on the marble joint specimen. It indicated from the comparison that the results of void model are closer to experimental results than that resulting from cubic law and there existed a difference between void model and experimental results. And the reasons resulting in the difference were discussed.

Select

COUPLED HYDRO-MECHANICAL MODELING OF ROCK FRACTURES SUBJECT TO BOTH NORMAL STRESS AND FLUID PRESSURE

XIE Ni1，2，XU Lihua1，SHAO Jianfu2，FENG Xiating3

2011, 30 (S2): -3803
Full Text:

[PDF 0 KB] (910)

+

Show Abstract

A coupled mechanical-hydraulic model for a single saturated fracture under both normal stress and fluid pressure is proposed based on the classic Biot poroelasticity theory. By taking the fracture as assembling of a set of voids in rock mass，a generalized Biot coefficient is introduced to describe the interaction effect between pore fluid pressure and fracture deformation. Compared with the classic concept of effective stress proposed by Terzaghi，the generalized Biot coefficient in this model is not a constant but a function of fracture deformation，so that the dependency of the effect of fluid pressure on fracture deformation is emphasized. With the help of the generalized Biot coefficient，a nonlinear constitutive equation for a single fracture under both normal stress and fluid pressure is developed. Later，the mechanical deformation of the fracture is related to the fracture hydraulic conductivity through “cubic law”，so that a coupled mechanical-hydraulic model is developed. All the four parameters involved in this model have their physical significances and can be determined through mechanical compression tests and permeability tests. A first validity of the model is made by predicting the variation curve of fracture flowrates versus normal stress under different fluid pressure. Comparison between model prediction and tests data verifies the applicability of the proposed model.

Select

RESEARCH ON NONLINEAR CREEP MODEL IDENTIFICATION OF SILTITE IN THREE GORGES RESERVOIR AREA

HUANG Ming1，2，LIU Xinrong2

2011, 30 (S2): -3810
Full Text:

[PDF 0 KB] (737)

+

Show Abstract

For study on the nonlinear creep model of T2b2 siltite in the Three Gorges reservoir area，a nonlinear viscoelasticity model that can well describe the creep property of siltite is established and the parameters are also obtained. Based on nonlinear rheological theory and stress-strain relation of T2b2 siltite，a modified Kelvin model and its creep equation are presented firstly. Through installing the swath model which can be expressed as a step function with N model in parallel，a revised N model is established. What?s more，through connecting revised N model with revised K model and H model in the form of series，an mBurgers model，which can well describe the nonlinear creep property of rock is established. According to nonlinear least squares theory and uniaxial creep test results of T2b2 siltite，the parameters of mBurgers model are obtained by inversion calculation. By substituting the parameters obtained on behalf of the inversion into the model and calculating the theoretical results，theoretical curve and test curve are well anastomotic，which indicates that mBurgers model can well describe the creep of T2b2 siltite.

Select

ANALYSIS AND 3D MODELING OF REGIONAL SOIL EXPANSIBILITY?S SPATIAL VARIABILITY

JIN Yi1，2，PING Rui1，PAN Mao2，QIAO Jinhai2

2011, 30 (S2): -3819
Full Text:

[PDF 0 KB] (787)

+

Show Abstract

Goal is to analysis and model the spatial variability of soil expansive property quantitatively. With the collected data of boreholes and soil samples，the spatial variability patterns of soil expansibility of Binhu District，Hefei City，are explored in different direction and scale. And then，the three-dimensional expansibility variation model is constructed by using universal Kriging method as the mapping tool through GSIS2.0. Analysis results are validated by cross-validation method. Based on the above results，taking the local weather and distribution of water system into account，quantitative analysis and assessment of potential hazard from expansive soil are performed and some suggestions were proposed for civil planning and developing of the underground space. The research showed that three-dimensional analysis and modeling of subsurface geological environmental attributes is an effective，scientific，intuitive methodology for underground space planning and development，and it is also an effective mean for the attributes? quantitative analysis and assessment.

Select

STUDY OF DAMAGE VISCOELASTO-PLASTIC DYNAMIC CONSTITUTIVE MODEL OF ROCK MATERIALS

ZHAI Yue1，ZHAO Junhai2，LI Xunchang1，REN Jiancheng1

2011, 30 (S2): -3824
Full Text:

[PDF 0 KB] (803)

+

Show Abstract

For the dynamic mechanical properties of the rock materials，based on the statistical damage theory and constitutive model theory，the rock can be classified as a heterogeneous material which is made up of damage element，elastic element，plastic element and viscosity element. Consequently，based on above theory，the damage viscoelasto-plastic dynamic constitutive model of rock materials are constructed. Then，based on the data of dynamic impact test of rock，the characteristic parameters of dynamic constitutive functions of granite and concrete are ascertained by the inverse analysis method which is programmed by embedding the Nelder-Mead method in basic adaptive genetic algorithms by coding in real number. The result illustrate that stress-strain curve and experiment curve，which are both come from dynamic constitutive model，have a great consistency. Consequently，the applicability of damage viscoelasto-plastic dynamic constitutive model has been verified.

Select

STATISTICAL ANALYZING OF ROCK MASSES STRENGTH PARAMETERS BASED ON CLASSIFICATION

ZHANG Yihu，ZHOU Huoming，WU Aiqing，ZHONG Zuowu，QIN Lei

2011, 30 (S2): -3830
Full Text:

[PDF 0 KB] (936)

+

Show Abstract

186 samples of in situ rock masses strength parameters testing values，which include 7 samples of class I，41 samples of class II，46 samples of class III，76 samples of class IV，16 samples of class V，are screened out based on in-situ testing datum of CRSRI and information collected in Rock Masses Strength Parameters. By statistical analyzing，the scope of strength parameters of each class is given out，and the scopes are compared with the suggesting values in Standard for engineering classification of rock masses. Result indicates that the suggesting values in Standard for Engineering Classification of Rock Masses is much lower and needs to be corrected. 110 samples of geological suggestion values，which include 12 of class I，22 of class II，28 of class III，30 of class IV，18 of class V，are also screened out based on engineering geological datum of above 40 typical projects. The scope of geological suggestion values of each class is then given out，and compared with the values in Code for Engineering Geological Investigation of water resources and hydropower. Result indicates that the two scopes consist with each other well. Researching achievements can not only be helpful in standards or codes modification，but also be meaningful in enhancing the understanding of rock masses strength for engineers.

Select

ANALYTICAL SOLUTIONS OF CIRCULAR TUNNEL UNDER TWO-DIMENSION UNEQUAL PRESSURE CONSIDERING DILATANCY AND SOFTENING

BIAN Kang1，XIAO Ming2

2011, 30 (S2): -3838
Full Text:

[PDF 0 KB] (736)

+

Show Abstract

Base on the elastoplastic softening model and non-associated flow rule，the lateral pressure coefficient，the included angle with the polar axis and principal stress corresponding relations under different engineering conditions are considered. Combine with the strain softening and dilatancy characteristic of rock after it comes into the yield stage，the analytical solutions of elastoplastic stress，displacement and plastic radius of the circular tunnel are deduced. The result of computation example shows that the lateral pressure coefficient and principal stress corresponding relations decide the distributing shape of plastic zone nearby the tunnel. Dilatancy has a much more important influence on the rock displacement nearby the tunnel than on the plastic radius. The influence of dilatancy extent to the deformation nearby the tunnel becomes larger when the strain softening characteristic of surrounding rock increases. In the project which is controlled by the displacement nearby the tunnel，the influence of strain softening and dilatancy can not be ignored.

Select

FRACTAL ANALYSIS OF THREE-DIMENSIONAL TOPOGRAPHY CHARACTERISTICS OF ROCK JOINT SURFACE

CAO Ping，JIA Hongqiang，LIU Taoying，PU Chengzhi，FAN Xiang

2011, 30 (S2): -3843
Full Text:

[PDF 0 KB] (815)

+

Show Abstract

The surface of joint specimen has been scanned by using 3D surface profiler Talysurf CLI 2000 and the surface shape is numerical expressed in order to implement the 3D visualization of joint surface. Then，after the analysis of 3D surface topography characteristics with fractal geometric theory，the function，connected with fractal dimension and JRC of joint profile，is put forward. By taking a single joint surface as the research object，this paper probes into the relation between the fractal dimension of joint profile，JRC and the fractal dimension of joint surface，which has important significance in introducing fractal geometric theory to research the joint surface state.

Select

FRACTURE EVOLUTIONARY RULES OF MUDSTONE UNDER COUPLED COMPRESSION AND SHEAR AND ITS FRACTAL CHARACTERISTICS

CHAI Zhaoyun1，2，KANG Tianhe1，CHEN Weiyi2，YANG Yongkang1

2011, 30 (S2): -3850
Full Text:

[PDF 0 KB] (812)

+

Show Abstract

Based on the shear test with variable angle for pressure punch of mudstone samples in natural moisture condition，the fracture evolutionary rule and fractal characteristics of fracture blocks distribution of mudstone under compression and shear loading are studied by using nonlinear fractal theory. The research results are as follows：(1) The cohesion and friction angle parameters of rock samples are achieved by draw Mohr’s strength envelope according to the test date of shear test with variable angle for pressure punch. (2) The shape of load-load point displacement curves of rock sample under compression and shear loading is similar to complete stress-strain curve of rock sample under uniaxial compression，can be divided into compaction，elastic，plastic and fracture etc four stages，and faithfully represent the failure process of rock samples under coupled compression and shear. (3) Compression and shear failure is the nonlinear energy dissipation dynamics process，fracture blocks distribution has self-similarity obviously，and can use fractal dimension characterization its size distribution character. (4) Fractal dimension of fracture blocks distribution decrease logarithm with shear angle increase because of dominate fracture type transformed from splitting fracture into shear fracture.

Select

RESEARCH AND APPLICATION OF PREDICTING ANTI-DRILLING PARAMETERS OF CARBONATE FORMATION

ZOU Deyong1，CAO Jifei2，YUAN Jun1，SUN Yuanxiu1

2011, 30 (S2): -3856
Full Text:

[PDF 0 KB] (795)

+

Show Abstract

As the important formation that is rich in oil and gas，predicting anti-drilling parameters of carbonate formation is the guarantee for efficient development of oil and gas. Based on anti-drilling parameters measured in lab and on-site logging data，the correlations of the rock drill ability and compressional wave offset time，compressive strength and compressional wave offset time，plasticity coefficient and Poisson's ratio，and the correlation between compressional wave offset time of rock surface and the down hole-logged compressional wave offset time，compressional wave offset time and shear wave offset time were studied by means of mathematical statistics. The mathematical models were established to predict anti-drilling parameters of carbonate formation. By substituting the logging data into the prediction model for calculations，the prediction accuracy is up to 90%. Using the established mathematical models，the anti-drilling characteristics of marine formation in Yuanba block were researched and that will provide the reasonable basis for bit selection and drilling parameters optimization.

Select

INVESTIGATION ON CONVENTIONAL TRIAXIAL COMPRESSION TESTS OF DUCTILE ROCK AND LAW OF DEFORMATION AND DAMAGE EVOLUTION

ZHANG Zhiliang1，2，XU Weiya1，2，WANG Wei1，2，WANG Rubin1，2

2011, 30 (S2): -3862
Full Text:

[PDF 0 KB] (786)

+

Show Abstract

The rock sample is strongly weathered sandstone which is from the compressive zone of the dam foundation of Xiangjiaba hydropower station，and the conventional triaxial experiments under different confining pressures are carried out for the rock by using automatic triaxial servo-instrument. The deformation and failure mechanism of rock are studied. The results show that the rock has significant characteristics of non-linear deformation and ductile failure，so it belongs to ductile rock. In the action of deviatoric stress，the axial and lateral strain of rock reaches 5% and 4% respectively，and the volume expansion strain reaches more than 4%.The deformation mechanical parameters of rock change with the loading. With the increase of deviatoric stress，elastic modulus of the rock decreases as well as Poisson?s ratio increases. The confining pressure enhances the rock resistance to deformation and failure. The greater the confining pressure，the larger the initial expansion deviatoric stress of rock. Based on the density method，the damage evolution of rock is discussed. At the initial loading state，the rock is compacted without damage；when the deviatoric stress exceeds a certain level，the rock damage increases as a linear relationship with the equivalent strain，and the density damage threshold is lower than 0.12. The experiment results offer important reference value to the research of stability of the dam foundation of Xiangjiaba hydropower station.

Select

PARAMETERS IDENTIFICATION OF PROBABILITY-INTEGRAL METHOD BASED ON MULTI-SCALE KERNEL PARTIAL LEAST-SQUARES REGRESSION METHOD

WANG Zhengshuai1，2，DENG Kazhong1，2

2011, 30 (S2): -3870
Full Text:

[PDF 0 KB] (846)

+

Show Abstract

Aiming at the prediction shortcomings of the traditional nonlinear modeling methods，including partial least-squares regression(PLS)，artificial neural network(ANN) and support vector machines(SVM) using probability-integral method，a novel method named multi-scale kernel partial least-squares regression(multi-scale KPLS) is proposed to identify parameters of the probability-integral method. Firstly，an admissible multi-scale Gaussian kernel function is constructed. Secondly，fuzzy clustering is applied to determine the optimal number of categories，which is regarded as scale parameter，and then，all kernel widths are optimized by 10 times 10-fold cross-validation and grid search method. Finally，the modeling process was discussed detailedly. Contrasting the prediction results of multi-scale KPLS with other methods of PLS，RBF neural network(RBF-NN) and SVM respectively，it shows that the former?s prediction accuracy is obviously better than the others? because of considering the characteristic of multi-scale in modeling samples；multi-scale KPLS has a stronger robustness and efficiently overcomes the multicollinearity between factors effecting on prediction results disadvantageously；multi-scale KPLS is suitable for parameters identification of probability-integral method with several induced variables versus several independent variables and its parameters could be determined by self-adaptive，so by terms of modeling efficiency，it is better than RBF-NN and SVM.

Select

STUDY OF ACOUSTIC EMISSION CHARACTERISTICS OF LIMESTONE UNDER CYCLE UNIAXIAL LOADING- UNLOADING PERTURBATION

BAO Chunyan1，2，JIANG Annan1，TANG Chun?an2，LIANG Zhengzhao2

2011, 30 (S2): -3877
Full Text:

[PDF 0 KB] (781)

+

Show Abstract

Take limestone samples from metro Line 2 as research objects，and study acoustic emission(AE) characteristics under uniaxial cyclic load-unload disturbance，which simulate the traffic load disturbance，then carry out numerical simulation of rock failure process under load-unload by RFPA2D. The results confirmed the existence of Kaiser effect of such limestone，also confirmed the existence of Felicity effect under loading- unloading. Loading and unloading theory will be applied to the rock acoustic emission precursor analysis，taken the Y value(load/unload response ratio，LURR) reach(close) to 1 as a precursor of failure characteristics of such rock. The AE energy of such stone accelerated release obviously. The numerical simulation shows evident Kaiser effect，and the corresponding AE event vividly. The comparison of the results of simulation and tests shows that，the two are the most closed when the coefficient of homogeneity m is 5. The results are expected to provide basis for construction safety and to avoid geological disaster in the underground works.

Select

INVESTIGATION ON THREE-DIMENSIONAL OVERBURDEN PRESSURE CALCULATION METHOD

FAN Honghai，YE Zhi，JI Rongyi，ZHANG Hongbao，LI Xuge

2011, 30 (S2): -3883
Full Text:

[PDF 0 KB] (658)

+

Show Abstract

This paper presents a new model for 3D overburden pressure estimation，which is based on single point algorithm hypothesis. In this model，the 3D seismic data is combined with drilled well information and geological stratification information，greatly improves the calculation precision of 3D overburden pressure field. This model consists of three steps：first，3D density volume is obtained by logging constrained seismic inversion；second，overburden pressure data is calculated from inversion density data point by point，on basis of single algorithm and spatial interpolation；finally，3D overburden pressure volume is rebuilt by spatial interpolation calculation. A computer program is developed，and a seismic zone of the Yinger depression in Jiudong basin is taken as a calculation example. Compared with the overburden pressure of drilled wells in this zone，the results proved the accuracy and applicability of this model.

Select

A PHYSICAL MODELING STUDY OF WATER FLOW AND HEAT TRANSFER IN UN-FILLED FRACTURED ROCKS

LU Wei，XIANG Yanyong，LI Tao

2011, 30 (S2): -3891
Full Text:

[PDF 0 KB] (699)

+

Show Abstract

The characteristics of water flow and heat transfer in fractured rocks is an important component for the performance and safety evaluation of high-level radioactive nuclear waste repositories. A meter-scale physical modelling experiment is conducted to study the behaviour of flow and heat transfer in multi-fractured rocks with variable heat source temperature and water flow velocity. The granite rocks are taken from the Beishan area in Gansu province，which is being investigated as potential site for the high-nuclear waste repository in China. The fractured rock model of 150.25 cm×90.4 cm×30 cm(height×width×thickness) consists of 18 granite rocks with 2 vertical fractures and 2 horizontal fractures；a heater is placed on one side of the fractured rock model and thermal sensors and pressure sensors are installed in the interior. The experimental results reveal that：(1) since there exists a distance between the heat source and the vertical fractures，heat conduction and fracture water flow are not significantly coupled until after one hour of the experiment；(2) at the junction of vertical and horizontal fractures，due to local heat convection，the temperature of water in the vicinity is significantly increased；(3) the range of influence of the heat source is larger，and the time for asymptotically approaching steady-state is longer，for higher heat source temperatures and lower water velocities in the fractures；(4) vertical fracture adjacent to the heat source controls the temperature distribution in the model，and the horizontal fractures may increase the range of influence of the heat source；(5) under the given conditions，with the vertical fracture water temperatures well below 100 ℃，there is little effect on the water pressure.

Select

CHARACTERISTICS OF DEFORMATION，FAILURE AND STRAIN ENERGY OF SANDSTONE UNDER CYCLING LOADING IN POST-PEAK

GUO Chenye1，2，XIAN Xuefu1，JIANG Yongdong1，WANG Chen1

2011, 30 (S2): -3898
Full Text:

[PDF 0 KB] (731)

+

Show Abstract

In order to understand the characteristics of deformation，failure and strain energy of the fractured rock sample under continuous loading，triaxial compression tests of the sandstone sample from Yongchuan mine are carried out by a MTS815 rock testing system. Based on the experimental results，the fractured ratio(r) is developed，it reflects the ratio of the break between the fractured sample and the perfect sample，smaller r means the larger fracture for the rock sample，the maximum and the minimum value of r is 1 and the ratio of residual strength and peak strength. The results of this analysis showed that the fractured ratio has good linear relationship with the secant modulus，axial strain，Poisson?s ratio and strain energy；after continuous loading，the failure mode of fractured rock sample appears‘X’shear failure mode；the maximum of Poisson?s ratio of rock can be determined by the test under continuous loading. These conclusions have a great significance to understand the mechanism of rock outburst and rockburst.

Select

STUDY OF VISCOPLASTIC STRAIN RATE METHOD TO QUICKLY DETERMINE LONG-TERM STRENGTH OF ROCK

CUI Xuan1，2，SHE Chengxue1

2011, 30 (S2): -3904
Full Text:

[PDF 0 KB] (761)

+

Show Abstract

A new method to determine the long-term strength of rock with quick creep test is proposed. Firstly，the linear relationship of the viscoplastic strain rate and the loading stress is discussed，and it is illustrated theoretically that only if the viscoplastic strains under different stress levels can be measured，the long-term strength of rock can be determined. And then a method is proposed to separate the viscoplastic strain increment from the total strain increament，in which the creep tests under lower stress are used to establish the viscoelastic creep model to determine the viscoelastic strain increment under higher stress level. Thirdly，the conventional multi-stage creep test for marbles is conducted to check the correctness of the proposed method. And fatherly，the creep test with shortening loading time is also conducted to check the feasibility to shortening test time. The results demonstrate that the proposed method is correct；and under the condition of shortening loading time，the long-term strength of rock is determined correctly showing the feasibility of shortening loading time. These works have demonstrated that the proposed method has the characteristics of quick creep test，computer programming and excluding the personal influence. Furthermore the method can well adapt the fluctuation of deformation measuring values during creep test. It is forecasted that the proposed method will have good application in engineering.

Select

RESEARCH ON ANALYTICAL SOLUTION OF STRESS FIELD OF SURROUNDING ROCK OF SINGLE HOLE WITH ARBITRARY SHAPE BASED ON HIGHLY-EFFICIENT CONFORMAL MAPPING

HUANGFU Pengpeng，ZHANG Luqing，WU Faquan

2011, 30 (S2): -3913
Full Text:

[PDF 0 KB] (798)

+

Show Abstract

The general steps of calculating analytical solution of stress field of the surrounding rock of single hole with arbitrary shape and analytical expression of the two potentials were obtained，based on highly-efficient conformal mapping of external area of underground cavern with arbitrary shape based on searching mapped points on the boundary，Cauchy integral formula，combined with complex function method. Then，the stresses at any point z inside the surrounding rock can be computed by using the Kolosov-Muskhelishvili formulae fast. Compared with numerical result，the result acquired by this analytical algorithm could be much more precise than that of the numerical simulation，and the former is much more efficient，too. Then，the analytical result of stress field of the surrounding rock of hole with straight wall and horseshoe shape under three cases of remote loading were obtained using this method，and zones of stress concentration were denoted emphatically. Finally，using this method，the analytical solution of stress field of the surrounding rock of the main power house of Jinping I hydropower station was calculated.

Select

RESEARCH ON RELATIONSHIP OF ROCK MASS INTEGRITY INDEX AND ROCK MASS ELASTIC MODULUS

GUO Qiang1，GE Xiurun1，2，CHE Ailan1

2011, 30 (S2): -3919
Full Text:

[PDF 0 KB] (747)

+

Show Abstract

Research and test have proved the closeness between elasticity modulus and integrity index of rock mass. The elasticity modulus can be indirectly inferred from the study of rock mass integrity. The borehole image technology and its analytical approaches are used to get the rock mass integrity index(RMDI)，which is deduced to have negative linear correlation with rock mass elasticity modulus when it was kept constant. The conclusion is proved to be right by the on-site trial. Otherwise，it contrasted the correlations of RMDI and rock quality designation to the elasticity modulus of rock mass，the result showed that RMDI and elasticity modulus has higher dependency.

Select

MECHANISM STUDY OF OVERLYING STRATA MOVEMENT INDUCING ROCKRURST ON TOP-COAL CAVING FACE

HE Jiang，DOU Linming，HE Hu，LU Zhenyu，LU Changguo，GUO Xiaoqiang

2011, 30 (S2): -3927
Full Text:

[PDF 0 KB] (719)

+

Show Abstract

Based on the voussoir beam theory，the bi-directional(up and down wards) movement model of top-coal caving face was promoted. Accordingly the energy and stress sources of rockburst were analyzed. By the seismic observation technology，the microseism(MS) effect of the overlying strata movement was observed and the achieved results are as follows：(1) the MS activity is periodic，before rockburst，the total energy continuously gets larger，and when rockburst happens，it gets up to the largest，and then it drops extraordinarily；(2) before rockburst happens，the events firstly get higher and then drop. The rockburst happens during the process of events reducing；(3) the average elevation can reflect the development state of the movement of overlying strata. Before rockburst happens，the average elevation gets higher，and when or pre of the rockburst，the elevation gets up to the largest value，while it drops abruptly after rockburst happening：(4) during the MS activity cycle，the spatial distribution of seismcities gets higher in elevation and vast in space before rockburst. When rockburst happens，it gets up to the peek values and the strata near the working face active strongly. As a result，the rockburst mainly happens during the overlying strata moving downwards，hence it?s possible to observe and prevent rockburst by monitoring the upward movement of the overlying strata.

Select

EFFECT OF CONFINING PRESSURE ON REPRESENTATIVE ELEMENTARY VOLUME SIZE OF JOINTED ROCK MASS

MA Chaofeng1，2，3，LI Xiao3，JIE Yuxin1，WANG Duli2，WANG Gang4

2011, 30 (S2): -3936
Full Text:

[PDF 0 KB] (672)

+

Show Abstract

The mechanical properties of jointed rock mass are closely related to its occurrence of stress state. None of the existing methods in obtaining representative elementary volume has taken the effect of confining pressure on representative elementary volume(REV) size into account. Based on certain road tunnel project，this issue is studied with 3D discrete element method in this paper. The dominant joint sets of rock mass are calculated based on a large number of joint surveys in our study area. Then，the structure model and 3D discrete element model of rock mass are built，which are further employed to simulate the compression test of rock mass，thereby employing the effect of confining pressure on REV size，deformation and mechanical properties of rock mass. The results indicate but not limit to the following conclusions：when confining pressure is less than 20 MPa，REV size is positively correlated with the increase of confining pressure；when the confining pressure is greater than 20 MPa，REV size keep constant；when the confining pressure is less than 60 MPa，the capacity of rock mass is positively correlated with the increase of confining pressure；when the confining pressure is greater than 60 MPa，the rock mass capacity did not change as the confining pressure increasing. In addition，the axial strain，lateral strain and volumetric strain also showed significant effect of confining pressure.

Select

SEMI-ANALYTICAL SOLUTION OF ONE-DIMENSIONAL CONSOLIDATION WITH NON-DARCIAN FLOW CONSIDERING TIME-DEPENDENT LOADING

LI Chuanxun1，2，HU Anfeng1，XIE Kanghe1，WANG Yulin1

2011, 30 (S2): -3943
Full Text:

[PDF 0 KB] (826)

+

Show Abstract

A semi-analytical method，combining analytic solution for linear consolidation of layered soils with numerical discretization，is adopted to consider one-dimensional consolidation with non-Darcian flow under time-dependent loading，and semi-analytical solutions for this problem are obtained. The reliability of semi-analytical solutions was verified by comparing semi-analytical solutions to analytical solutions with Darcy?s flow and finite difference solutions with non-Darcian flow. Then consolidation behavior under various parameters is analyzed by a series of computation，and the results show that the parameters of non-Darcian flow have great influence on consolidation behavior；the greater the exponent and critical hydraulic grade，the slower the rate of consolidation；external load and the thickness of soil layer have great influence on consolidation behavior；the larger the load，the faster the rate of consolidation；the thicker the thickness of soil layer，the slower the rate of consolidation. Based on this non-Darcian flow，the similarity relationship that consolidation time is proportional to the square of the thickness of soil layer in classic theory of consolidation is no longer satisfied. The faster the loading rate，the faster the rate of consolidation. Finally，applicability of Darcy?s flow law to one-dimensional consolidation is analyzed.

Select

STUDY OF MECHANICAL PROPERTY OF LIMESTONE SPECIMENS WITH NATURAL CONTINUOUS WEAK PLANE

SU Chengdong，WU Qiuhong

2011, 30 (S2): -3952
Full Text:

[PDF 0 KB] (693)

+

Show Abstract

In order to study the effect of natural weak plane on mechanical properties of rock，40 limestone intact specimens and specimens with the angle of natural continuous weak plane ranged from 53° to 90° are carried out longitudinal wave velocities，uniaxial and pseudo-triaxial compression. The tests indicate that：longitudinal wave velocities，dip of specimens with weak plane，and uniaxial compressive strength have no certain relationship. Failure modes of specimens have three types，sliding-failure along the weak plane，shearing-failure across the weak plane and comprehensive failure，when the angle of specimen with weak plane ranged from 65° to 80°，it takes place sliding-failure along the weak plane，its strength is obviously lower，when the angle of specimen with weak plane is less than 65° or greater than 80°，it takes place shearing-failure across the weak plane，the strength and the fracture angle approximately meet Coulomb strength criterion；Two specimens take comprehensive failure，the strength of comprehensive failure is between shearing-failure across the weak plane and sliding-failure along the weak plane. The filling material of weak plane of limestone is approximately to main body，which has same internal friction coefficient 0.944 with intact specimens. The material strength of 40 specimens that the strength of triaxial compression deducts confining pressure is between 30.3 and 177.1 MPa，the average is 121.3 MPa，the standard deviation is 32.6 MPa，which roughly conform to normal distribution；The orientation of the weakest plane of rock varies with specimen whose cohesion is significant difference，which makes significant different the strength and failure modes of triaxial compression.

Select

MESO-EXPERIMENTAL INVESTIGATION ON CRACK EVOLUTION IN BEDDED SALT ROCK

PENG Ruidong 1，2，WU Zhide2，ZHOU Hongwei2，ZUO Jianping2

2011, 30 (S2): -3959
Full Text:

[PDF 0 KB] (759)

+

Show Abstract

Investigation of mechanical behavior of bedded salt rock is the scientific fundamental for constructing storage cavern in underground salt rocks. By means of an advanced testing system which can be used to observe real-time SEM images of samples under the condition of loading in situ，the evolution of cracks was investigated during bedded salt rock samples have being broken and the meso-mechanism is discussed based on the analysis of energy dissipation and energy release. It is observed that there exists large different between the meso-structure of rock salt and that of mud rock impurity in bedded salt rock，and such difference affect the micro mechanical behavior of bedded salt rock. Cracks never develop along the interface of rock salt and mud rock impurity，and they usually develop in rock salts or mud rock impurities. When cracks are developing in the mud rock impurity，energy dissipation plays an important role so that the path of cracks is irregular which fractal dimension is large than 1 and even branch out sometimes，and under this case the load-bearing capacity of bedded rock is weak so that it would rupture although the work of external load is still small. When cracks are developing in the rock salt，more elastic energy is released quickly so that the path of cracks is straight which fractal dimension is nearly equal to 1 and even open more large distance sometimes，and under this case the load-bearing capacity of bedded rock is strong so that it could absorb more energy due to the work of external load.

Select

EXPERIMENTAL RESEARCH ON CREEP CHARACTERISTICS OF CHONGQING RED SANDSTONE UNDER DIRECT TENSION

ZHAO Baoyun1，2，LIU Dongyan1，2，ZHU Keshan1，ZHENG Zhiming1，3，XUE Kaixi1

2011, 30 (S2): -3965
Full Text:

[PDF 0 KB] (708)

+

Show Abstract

Taking Chongqing typical red sandstone for study object，direct tensile creep test of the red sandstone is conducted by self-designed and developed uniaxial direct tension device. Based on test results，the uniaxial creep laws of axial creep，lateral creep and unloading creep are studied，and the characteristics of creep ruptures are also discussed. Finally，the modified nonlinear Nishihara model is used to describe the creep process of sandstone. Based on the Matlab programming of Levenberg-Marquardt(LM) optimization algorithm，the parameters of modified nonlinear Nishihara model are obtained. Comparison between creep model and experimental results shows that the modified nonlinear Nishihara model is applicability in the direct tensile creep of red sandstone. Conclusions of the study enrich the creep data of red sandstone in Chongqing and have positive significance for large-scale geotechnical engineering in this region.

Select

EXPERIMENTAL STUDY OF FAILURE MODE OF SANDSTONE UNDER DIFFERENT LOADING PATHS

NIU Shuangjian1，JING Hongwen2，LIANG Junqi3

2011, 30 (S2): -3974
Full Text:

[PDF 0 KB] (808)

+

Show Abstract

As the existing studies in failure modes of rock under different loading paths are less，uniaxial compression，conventional triaxial compression，pre-peak and post-peak unloading confining pressure tests of sandstone are respectively conducted with the MTS815 rigid servo-controlling testing machine. Based on test results，the failure modes of sandstone under different loading paths are studied. According to the energy analysis of sandstone specimens before and after failure，the reasons for existences of different failure modes under different loading paths are discussed by means of energy dissipation theory. The results show that the main failure mode of sandstone specimens in uniaxial compression tests is splitting failure，while single shear failure is complement. The main failure mode is single shear or splitting failure under low confining pressure in conventional triaxial compression and post-peak unloading confining pressure tests；when the confining pressure is higher，combination failure modes of single shear and splitting failure mainly occurs. Under the per-peak unloading confining pressure tests，combination failure modes of shear and transverse shear of sandstone specimens mainly occurs under low confining pressure. On the contrary，combination failure modes of splitting and shear mainly occurs under high confining pressure. With the increasing confining pressure，shear failure occurs easily under triaxial compression；but the probability of shear failure occurrence increases at first，then decreases under pre-peak and post-peak unloading confining pressure. The failure modes under different loading paths are related with the energy values of sandstone specimens before and after failure. When the energy value is low，single failure mode occurs easily with intact broken block. When the energy value is high，combination failure modes occur easily with crushed block.

Select

EXPERIMENTAL INVESTIGATION ON SINGLE-PHASE NON-LINEAR FLOW IN LOW PERMEABILITY CORES

XIE Quan1，2，JIAO Chunyan2，CUI Liping3，HE Shunli2，LU Zhikai2

2011, 30 (S2): -3981
Full Text:

[PDF 0 KB] (804)

+

Show Abstract

The saturated seepage curves with the single-phase of the standard brine and kerosene in the low permeability full diameter core plugs from the Erdos basin have been measured through fully automatic flooding system——AFS300TM provided by Core Lab of America under low pressure gradient(0.005～0.300 MPa/m) with the steady state approach. Through the BP–100 air spring back to pressure valve，core outlet pressure is controlled. The experimental results indicate that the outlet flow rate of core plugs increases linearly with the increase of pressure gradient；and the phenomena of threshold pressure gradient and non-linearity are not observed in terms of saturated flow method. Moreover，obvious threshold pressure gradient is not observed in terms of unsteady state method. Single-phase non-linear flow in low permeability cores with Newtonian fluids-brine and kerosene meets Darcy law. The interaction force between the surface of pore and the standard brine and kerosene can not cause non-linearity and threshold pressure gradient of single-phase flow.

Select

EXPERIMENTAL STUDY OF INFLUENTIAL RULE OF FRACTAL INTERCEPT ON ENERGY DISSIPATION OF STRESS WAVE

LI Yexue1，2，PENG Qi 3，ZHU Jianbo3，LIU Jianfeng2

2011, 30 (S2): -3988
Full Text:

[PDF 0 KB] (725)

+

Show Abstract

Scanning experiment of rough fracture and impacting dynamics test of jointed granite is respectively conducted in order to investigate influential rule of geometrical characteristic of joint surface on energy dissipation of stress wave and establish quantitative relationship between fractal intercept and energy dissipation ratio contributed by intercept of stress wave across joint on the condition of fractal dimension 2.0≤D≤2.2. It is shown that contribution towards total energy dissipation ratio from fractal dimension is still primary；but in the interval，its contribution towards total energy dissipation ratio is constant and increment of total energy dissipation ratio is decided by fractal intercept. Energy dissipation ratio which is contributed by intercept of jointed rock decreases nonlinearly with the increasing of fractal intercept. By mechanism analysis，it is indicated that on the condition of similar impact loading，smaller shear displacement leads to less work and corresponding lower energy dissipation of stress wave because larger fractal intercept corresponds to higher shear stiffness. From microscopic view，during impacting loading，sample with larger fractal intercept brings lower probability of tiny plastic strain，crystal cracking，mutual impingement among molecule，so energy of stress wave is less dissipated.

Select

DYNAMIC TRIAXIAL EXPERIMENTAL RESEARCH ON DAMPING PARAMETERS AND DYNAMIC ELASTIC PARAMETERS FOR MARBLE

NIE Ming1，2，XU Jin1，2，REN Haonan1，2，LIU Jianfeng1，2

2011, 30 (S2): -3994
Full Text:

[PDF 0 KB] (676)

+

Show Abstract

The dynamic triaxial tests for marble under different confining pressure are conducted on MTS815 Flex Test GT rock mechanics test system for the first time. Damping parameters and dynamic elastic parameters of marble are tested. The sine wave is adopted in cyclic loading tests at the frequency of 3 Hz，and the cyclic number is 30. The upper limit of dynamic stress is 0.6 times of the compressive strength of specimen under corresponding confining pressure，while the lower limit of dynamic stress is 5.09 MPa. The research results are shown as follows：damping ratios，damping coefficients and dynamic Poisson?s ratios of marble decrease with the increasing cyclic loading number，while they increase with the increasing confining pressure. Dynamic elastic moduli increase with the increasing cyclic loading number，while they decrease with the increasing confining pressure. Dynamic elastic moduli are always greater than static elastic moduli，while dynamic Poisson?s ratios are always smaller than static Poisson?s ratios under different confining pressures；and the higher the confining pressure is，the greater the difference value is. Mechanical properties of marble are gradually reinforced within 30 dynamic loading cycles.

Select

STUDY OF DYNAMIC RESPONSE OF BRIDGE PIER SHOCKED BY FALLING ROCK INDUCED BY INTENSIVE EARTHQUAKE

PEI Xiangjun，HUANG Runqiu，LI Shigui

2011, 30 (S2): -4001
Full Text:

[PDF 0 KB] (718)

+

Show Abstract

In the high earthquake region of intensity VIII，dangerous rock mass slope of Xichongte bridge pier #16 at YK136＋097 along Ya?an—Lugu highway is selected as studying objects. The geology-dynamics model of dangerous rock bodies is constructed from steep structural plane tilting to the outside slope and weathering- unloading fracture. Monitoring points are placed at important places of slope body and bridge pier. Using the numerical analysis method of discontinuous deformation，the instability model，failure scale，motion trajectory of dangerous rock masses and their impact dynamic response characteristics on bridge pier are simulated. Evolution process is presented as follows：Under intense earthquake，horizontal earthquake force causes enlargement effect，which results in earthquake collapse and ejection of the rock masses at salient position at first. Next，shattering-sliding and disintegrating of the rock masses happens along unloading tension fracture surfaces in the middle of slope. At last，the whole landslide body slumps along controlling structural plane and impacts bridge pier. Statistical analysis of displacement and deformation feature of all monitoring points at slope body and bridge pier shows that the displacement from all monitoring points is positively correlated with earthquake rhythm. Under the influence of the impacting of instability rock and the pushing of accumulation rock，the deformation and permanent displacement of beam and the top of pier are larger than that at other positions，which is the same as phenomenon of bridge failure during “5•12” Wenchuan earthquake. Based on the quantitative analysis of deformation of slope and pier，according to the collapse features induced by intense earthquake，prevention and treatment measurement are put forward for the dangerous rock mass of bridge slope.

Select

NUMERICAL DETERMINATION OF STRENGTH PARAMETERS OF FRACTURED ROCK MASSES USING FINITE ELEMENT METHOD

YANG Jianping1，CHEN Weizhong1，2，WU Guojun1，DAI Yonghao1

2011, 30 (S2): -4010
Full Text:

[PDF 0 KB] (788)

+

Show Abstract

The equivalent strength parameters of fractured rock masses are prerequisite to stability analysis of geotechnical engineering projects constructed in fractured rock masses which are encountered frequently in west China. Based on generated mesh of fractured rock masses，combined with statistic damage constitutive model of intact rock and damage model of structural plane，progressive failure of fractured rock masses is studied using finite element method(FEM). Furthermore，scale effect and anisotropy of compressive strength of fractured rock masses are studied. Study results show that the strength decreases and tends towards stability rapidly from intact rock to fractured rock masses，and the anisotropy of strength of fractured rock masses is not significant. At last，based on numerical simulation conducted on 10 m scale rock masses under different confining pressures，the equivalent strength parameters of fractured rock masses are gained and the results are compared with Hoek-Brown criteria. The method developed is helpful for determination of strength parameters of fractured rock masses.

Select

MODIFICATION AND APPLICATION OF CRITICAL WATER OUTBURST COEFFICIENT IN COALMINE BASED ON THE CONCEPT OF EFFECTIVE STRESS

YANG Tianhong1，LIU Honglei1，ZHU Wancheng1，MENG Zhaoping2，WANG Rui2

2011, 30 (S2): -4018
Full Text:

[PDF 0 KB] (863)

+

Show Abstract

Water outbursts from coalmine floor and hydraulic fracturing have the homologous mechanical mechanisms，which are all to determine the critical water pressure during failure process(water outburst coefficient is defined as critical water pressure per unit thickness of floor). The effect of effective stress coefficient is remarkable through hydraulic fracturing theoretical analysis. The influence of different effective stress coefficients during the process of water outburst in coal mine floor is discussed from static and transient aspects by in-situ case simulation，respectively. The formula of modified critical water outburst coefficient under different seepage conditions in coal mine floor is derived according to the theory of effective stress. Finally，calculation and field test methods of modifying water outburst coefficient are proposed according to different seepage conditions in coal mine floor，which have significant theoretical and practical senses for understanding the essences of water outburst induced by rock failure，the connotation of water outburst coefficient，and the guidance of seepage control design by grouting.

Select

STUDY OF CALCULATING METHODS FOR BEARING CAPACITY OF DEEP-ROCK-SOCKETED PILE

DAI Guoliang1，GONG Weiming1，CHENG Ye1，2，MENG Lijun1

2011, 30 (S2): -4024
Full Text:

[PDF 0 KB] (753)

+

Show Abstract

Based on the database of 120 piles tests，for the calculations of bearing capacity of the deep piles (the socket depth greater than 5 times pile diameter) used in large highway bridges and culverts，considering the form and ideas in the specification[1]，the factors of frictional resistance and base resistance related to the corresponding unconfined compression strength are analyzed for different ranges of unconfined compression strength and introduced in the formula. To verify the calculation formula，ultimate bearing capacity of tested piles of four projects，including Xihoumen Highway Bridge，Qingdao Bay Bridge，Jinyue Yangtze River Highway Bridge，and Balinhe River Highway Bridge，are checked. The results showed that calculated and measured values are in good agreement，to meet the engineering design requirements.

Select

STABILITY PROBABILITY CLASSIFICATION METHOD FOR ROCK SLOPE IN HYDROPOWER ENGINEERING REGIONS

LI Xiuzhen1，2，KONG Jiming1，2，LI Shengwei3

2011, 30 (S2): -4032
Full Text:

[PDF 0 KB] (798)

+

Show Abstract

Firstly introduced a slope stability probability classification(SSPC) method，which was proposed by Dutch scholar R. Hack，et al[1-3]. The method has two main limitations in the evaluation of rock slope stability of hydropower engineering regions. One is that the method is valid only for the slopes with heights ranging up to 45 m，another is that the estimation of the intact rock strength with broad bands in SSPC has strong subjectivity and randomness. To the two limitations，the shear strength of the slope rock masses is modified by Hoek-Brown strength criterion，and the maximum height of the slopes is calculated by using an empirical formula. The analysis results of 34 typical rock slopes(10 non-structure controlling slopes and 24 structure controlling slopes) of hydropower engineering regions show that the assessment accuracy of the modified method is 61.8% for the all 34 slopes and 80% for the 10 non-structure controlling slopes. So，the modified SSPC method is good for slope stability probability classification and can provide a new way for quick and effective assessment of rock slope in hydropower engineering regions.

Select

NUMERICAL IMPLEMENTATION AND APPLICATION OF THE TRIPLE SHEAR ENERGY CONSTITUTIVE MODEL OF GEOMATERIALS

GAO Hong 1，ZHENG Yingren1，2

2011, 30 (S2): -4038
Full Text:

[PDF 0 KB] (877)

+

Show Abstract

Based on the plastic potential theory，the numerical scheme in FLAC3D of the triple shear energy constitutive model suggested by the authors is studied. The numerical format of the model is derived，and the corresponding UDM interface codes are programmed. Considering that under conventional triaxial condition，the triple shear energy criterion is simplified to the Mohr-Coulomb criterion，the triple shear energy model and the Mohr-Coulomb model are used to numerical simulation of sample triaxial test. The two models give almost completely the same results，which verify the validity of the numerical scheme and the codes. Then the engineering application of the triple shear energy model is researched. The Prandtl analytic solution，the Mohr-Coulomb model，and the triple shear energy model are used to analyze the foundation bearing capacity. Because the Prandtl analytic solution is based on the Mohr-Coulomb criterion，the results of the Mohr-Coulomb model and the Prandtl analytic solution are almost the same. Owing to the consideration of the intermediate principle stress effect in the triple shear energy criterion and the lack of consideration in the Mohr-Coulomb criterion，the Prandtl analytic solution and the Mohr-Coulomb model are both more conservative than the triple shear energy model，so the limit bearing capacity computed by the former two is smaller than that of the latter.

Select

DESIGNED CALCULATION OF RIGID-PILE COMPOSITE FOUNDATION IN SOFT SOIL GROUND CONSIDERING DEFORMATION COMPATIBILITY OF PILE AND SOIL

LIU Peng1，2，YANG Guanghua1，3

2011, 30 (S2): -4046
Full Text:

[PDF 0 KB] (816)

+

Show Abstract

According to design specification，soft soil rigid pile composite bearing capacity of soil between piles are often use too high，the settlement of soft soil under the corresponding designed load is greater than the settlement of composite foundation. But this situation can not happen in reality. So the bearing capacity of soft soil is not fully functional as designed load in engineering practice. The main reason is not considered the pile-soil deformation compatibility. In order to reveal the intrinsic relationship between the deformation compatibility and bearing capacity of soft soil being used much higher than the reality，the p-s curve of the pile and soil respectively is calculated by the tangent modulus method. Then，the rigid-pile composite foundation?s p-s curve is determined by the p-s curves of the pile and soil. The relationship of the deformation compatibility of pile-soil will be established，on the basis of which the load-sharing case of the pile and soil can be analysed. It is found that the designed bearing capacity of soil is much higher than the reality based on normal design norms of composite foundation，while pile load is greater than the designed value. The bearing capacity or strength of pile is inadequate，which leads to foundation failure. For the lack of design norms methods，it was put forward that rational design of composite foundation should consider the deformation compatibility and bearing capacity of soft soil should be determined under corresponding the settlement in terms of its p-s curve. It is established the designed calculation of rigid-pile composite foundation in soft soil ground considering deformation compatibility of pile-soil. It provides a guide for design in the future.

Select

DEVELOPMENT OF WIRELESS SENSOR NETWORK TECHNOLOGY AND ITS CHALLENGES IN SUBWAY TUNNEL ENGINEERING

XIE Xiongyao1，2，FENG Lei1，2

2011, 30 (S2): -4055
Full Text:

[PDF 0 KB] (824)

+

Show Abstract

The structures will deteriorate with the extension of service life after the completion of civil engineering infrastructures. Structural health monitoring systems are widely adopted to monitor the behavior of structures and evaluate the safety and durability of structures. The monitoring of urban subway tunnel structures is significant and difficult due to combined effects of ground water erosion and train vibration loads，wireless sensor network(WSN) technology provide a promising method to monitor subway tunnel structures. Wireless sensor network provide advantages in cost，size，flexibility and distributed intelligence，compared to traditional wired monitoring method. However，as a emerging technology，there are some limitations for the application of WSN in subway tunnel monitoring，such as signal attenuation inside tunnel，node deployment，time synchronization，limitation of battery. The state of the art in wireless sensor network technology is reviewed，recent research and application activities on monitoring of civil infrastructures are briefly introduced. Challenges of the application of WSN in subway tunnel are analyzed and summarized，and the future research directions are discussed.

Select

ANALYSIS OF DYNAMIC STRESS STATE AND EFFECTIVE WORKING RADIUS IN SUBGRADE UNDER CONCENTRATED LOAD

TANG Liansheng1，2，LIN Peiyuan1，2，WU Ke1，DENG Xibin1，DING Qingfeng1，DENG Zhongwei1

2011, 30 (S2): -4063
Full Text:

[PDF 0 KB] (699)

+

Show Abstract

Based on the classical Boussinesq analytical solutions，a set defined by stress and strain state of points，when subjected to concentrated load，with varied spatial location in semi-infinite elastic subgrade and constrained by certain conditions，is employed to characterize the stress and strain state of a fixed point in the subgrade during the loading-unloading process induced by a single vehicle load. Dynamics，consequently，is transformed into quasi-statics，and analysis model，which is supposed to be convenient and practical for verifying subgrade dynamic behaviors，is established. Stress state and effective working radius are approached and determined during a loading—unloading process in subgrade. Results indicate：(1) curves of dynamic normal stress differences( ) and ( ) are pulse shape，while( ) changes in a twin peak manner；(2) the maximum principal stress might whirl abruptly about z axis，and the angle intersected with z axis rotates gradually and continuously by 180°；the orientation of minimum principal stress turns in a relatively smooth pattern and its rotation features are less remarkably；while the intermediate principal stress direction alters elusively；(3) effective working radius，which represents the limit of impacts exerted by a single vehicle loads on subgrade，pavement system，is suggested to a length of 10 m，and the influenced area can be considered as a semi-sphere with a radius of 10 m and whose center sited at the point of load. At last，the validity of effective working radius，which is defined by 10 m under one vehicle loading，is specified by in situ monitoring data.

Select

STUDY OF CRITICAL SLOPE DEGREE OF CHANNEL EXCAVATION BASED ON FINITE ARC AND STRENGTH REDUCTION METHOD

ZHANG Yu1，XU Weiya1，SHI Chong1，ZHANG Fangfang2

2011, 30 (S2): -4071
Full Text:

[PDF 0 KB] (843)

+

Show Abstract

Stress，strain and displacement in slope are calculated using the finite difference method. The finite arc method is presented based on the limit equilibrium theory and strength reduction method with deformation?s change trend as a standard of failure. The presented method is applied to search critical slip surface and the minimum safety coefficient of slip，and the case studies with verification and parameters? discussion demonstrates the accuracy in the application of slope engineering. The presented method and the limit equilibrium method are applied to study critical slope of one large channel excavation in South-to-North Water Diversion Project. In the study three typical channel?s slope modes including high slope，reclaimed slope and deep excavation slope mode are selected to get the safety coefficients? change with slope degrees of excavation，then the critical excavated slope of channel can be determined. The computed results show that high slope and reclaimed slope in the large channel require a high level for excavated slope degree. Compared to the excavation，the filling load owes more effect on the slope?s stability. It?s found that the presented methods in this paper more accurate and rational，which could complement the insufficiency of existing methods. The methods not only solve the design problems of large channel?s slope，but also provide a good reference for the similar slope engineering.

Select

DEFORMATION PREDICTING AND CONTRAST ANALYSIS OF RUNNING SUBWAY CAUSED BY SHIELD UP-UNDER CROSSING

YANG Yuheng，LIAO Shaoming，FAN Yaoyao，WU Jun

2011, 30 (S2): -4077
Full Text:

[PDF 0 KB] (808)

+

Show Abstract

Base on the up-under crossing running subway project in Shanghai metro construction，with the numerical simulation approach，the disturbance cause by shield crossing is analyzed under the sequence of under crossing first then up. The result shows that it could satisfy the operation and environment requirements when the ground loss rate is controlled to less than 3‰. For further analysis，the deformations caused by two cases of up-under crossing and up crossing only is compared. The result shows that the up-under crossing lead a larger rebound float owing to disturbing effect in advance. Finally，based the theoretical predictions and the difference between the two cases，a series of controlling measures to control the diversification are formulated. It provides a reference for the similar projects.

Select

MONITORING AND DEFORMATION FAILURE ANALYSIS OF RED SANDSTONE BEDDING SLOPE

FENG Zhen1，2，JIN Fuxi3，GONG Yifang4

2011, 30 (S2): -4086
Full Text:

[PDF 0 KB] (831)

+

Show Abstract

Because of the characteristics of weathering disintegrating easily，low long-term strength and argillization intercalation development for red sandstone，toe excavation produces enormous susceptible bedding slopes. Combining a construction project，the main reasons of red sandstone bedding slope failure are unfavorable geological structure，toe excavation and precipitation. According to long-term slope monitoring data，the slope is still in the stage of creep deformation after treatment of anti-slide piles and the slope and anti-slide piles deform to different extents. Based on previous research and data processing of long-term slope monitoring，analysis results indicate that the main reasons of deformation of slope and piles are continuous and intensive precipitation and sliding surface going deeper. New sliding surface is above stable underground water table，so that eluviations and water content increase of argillization intercalation could happen only under continuous and intensive precipitation which lead to shear strength reducing and residual sliding force increasing. Piles deform to adjust increasing residual sliding force.

Select

ROCK DAMAGE EVOLUTION BASED ON ENERGY PRINCIPLE

GAO Wei1，WANG Lei2，YANG Dayong3

2011, 30 (S2): -4092
Full Text:

[PDF 0 KB] (727)

+

Show Abstract

Rock is a kind of natural engineering material with genetic defects. For the complexity of its mechanical property，the mature model to describe rock damage process is not yet established. To solve this problem，from the basic isotropic damage，based on strain equivalent principle and least energy consumption principle，one novel damage evolutionary model of the rock from the energy principle is developed. From analysis the whole test process of granite block from meso-damage to macro fracture，the damage evolutionary model of granite is obtained based on energy principle. Compared to the computing results of traditional Marzars damage model，we can find that the new damage model proposed here can reflect the rock damage process more reliably，and coincide with the real fracture process of rock test very well.

Select

NUMERICAL SIMULATION ON INFLUENCE OF HETEROGENEITY ON MACROSCOPIC FRACTURE PROCESS OF ROCK FAILURE

KE Changren1，2，JIANG Junling2，GE Xiurun1，3，XIAO Benlin2

2011, 30 (S2): -4103
Full Text:

[PDF 0 KB] (632)

+

Show Abstract

Based on the virtual internal bond model，the influence of heterogeneity index on macroscopic behavior of rock failure is studied. It is deemed by discrete virtual internal bond model(VIB) that the solid materials are composed of quality materials at micro scale，the particles are connected by a VIB，based on a special cohesive force law，the VIB model could simulate the fracture of solid materials needing no fracture guideline，and the macro constitutive equation is drawn from the interactive of the particles. Two kinds of the elements’ state are proposed—the solid element and the air element，to describe the element?s condition under the pressure. By simulating the rock fracture process when the heterogeneity index m = 1.1，1.5，2.0，3.0，5.0，it is found that the heterogeneity has immense influence on the stress-strain curve and the fracture modes：with the higher heterogeneity index，the stronger linearity of the pre- stress-strain curve，and the higher peak stress，the deeper post stress-strain curve，and the fracture mode presents markedly brittle behavior.

Select

NUMERICAL ANALYSIS OF DEEP FOUNDATION PIT DISPLACEMENT WITH DOUBLE-ROW END-SUSPENDED PILES IN STRATA OF SOIL-ROCK DUALISTIC STRUCTURE

LIU Hongjun1，2，WANG Yajun2，JIANG Dehong3，ZHENG Jianguo1，2

2011, 30 (S2): -4103
Full Text:

[PDF 0 KB] (792)

+

Show Abstract

Many special supporting structures have arisen in deep foundation pits corresponding to different excavation methods，depths and geological conditions. In strata of soil-rock dualistic structure，design and construction experiences are far from adequate in double-row end-suspended piles. The supporting system of Kaiyue deep foundation pit in Qingdao is taken as an engineering case to simulate the excavation process with the finite element software Plaxis. And then，comparative analyses are carried out between analytical results and in-situ monitoring data. The results show that such double-row end-suspended piles has more stiffness and can effectively control the deformation of foundation pit and the displacement of the pile，which mainly concentrates in the depth range of soil strata. The conclusions can serve as a theoretical reference for the optimal design of similar support structures.

Select

EXPERIMENTAL STUDY OF SHOCK COMPRESSION PROPERTIES OF UNDERGROUND ENGINEERING ROCK UNDER ACTIVE CONFINING PRESSURE

LIU Junzhong1，XU Jinyu1，2，ZHAO Dehui1，BAI Erlei1，WANG Zhenyu3

2011, 30 (S2): -4109
Full Text:

[PDF 0 KB] (666)

+

Show Abstract

The mechanical properties of rock-like brittle materials are closely related to the confining pressure. In order to study the dynamic mechanical properties of rock under confining pressure and get its axial stress-strain curve under distinct confining pressures and strain rates，the underground engineering rock are subjected to impact compression experiments with the split Hopkinson pressure bar(SHPB) of diameter 100 mm with active confining pressure device. At the same time，the dynamic stress equilibrium of SHPB experiment is analyzed. Experimental results show that：(1) The dynamic compressive strength and toughening effects of rock are more prominent under confining pressure and appears development trends to ductile characteristic，which reveals a strong confining pressure effect. (2) Under the same range of confining pressure，rock?s peak strength and peak strain change with the strain rate and reveal significant strain rate dependence. The dynamic strength increase factor keeps an approximately linear relationship with the logarithm of strain rate and dynamic strength appears approximately linearly increase with the stain-rate upwards. (3) The rock demonstrates the obvious fragility characteristic under axial dynamic load. It damages under the action of many stresses combined and mainly by the tensile stress. With the confining pressure increasing，the rock sample reverses from brittle to ductile. Failure modes are characterized by compression shear damage going with tensile strain damage and unloading damage.

Select

FROZEN WALL DEFORMATION ANALYSIS IN WEAKLY CEMENTED SOFT ROCK BASED ON LAYERED CALCULATION OF STRENGTH

WANG Weiming1，2，WANG Lei1，2，DAI Chunquan1，2

2011, 30 (S2): -4116
Full Text:

[PDF 0 KB] (764)

+

Show Abstract

The weakly cemented soft rock has the characteristics of low strength，low frost heaving ratio and high theology effect. Traditional calculation method which substitutes average temperature for radial temperature gradient distribution of the frozen temperature field and substitutes average strength parameters for mechanical parameters radial hierarchical distribution can not reflect the deformation characteristic of the frozen wall in weakly cemented soft rock. The finite difference equation of layer model is given based on the model of power law constitutive relationship；and the implementation method of layer calculation model in FLAC3D is also given. The example analysis indicates that the results of layered calculation model are good agreement with the measured data. Based on the calculation result analysis in different working cases，the maximal displacement point of shaft wall in weakly cemented soft rock freeze sinking shaft is in the ranges of 0.36 h to 0.42 h. The h is the section height. The radial displacement of the free shaft wall is sensitive to the height of digging. With the increment of section height，surrounding rock deformation increases remarkably，and extends to deep freezing surrounding rock. An analysis of admissible free rib time shows that working face construction safety could not be assured during the normal shaft sinking time when the section height is more than 4.5 m.

Select

SEISMIC DESIGN STUDY OF HIGH SLOPE AT MAO STATION IN CHENGDU—LANZHOU RAILWAY

YE Hailin1，2，ZHENG Yingren1，2，LI Anhong3，DU Xiuli4，LAI Jie1

2011, 30 (S2): -4122
Full Text:

[PDF 0 KB] (769)

+

Show Abstract

In traditional seismic design of slope，the most commonly used method is the pseudo-static method. Because of its limitations，a new method of seismic design of the slope is proposed based on the strength reduction dynamic analysis. The proposed method takes into account the interaction between the supporting structure and rock soil under earthquake. It can satisfy the design requirements of earthquake and static stability of slope. The internal forces of supporting structure are obtained by the method. So，it ensures the safety and economics of engineering design. The seismic design of high slope of Mao railway station demonstrates the feasibility of the proposed method in practice，which provides a new idea for the seismic design of retaining the slope.

Select

COMPARISON OF THREE METHODS FOR GEOTECHNICAL CENTRIFUGE MODEL TESTS OF EXPLOSION CRATERING IN SAND

FAN Yikai1，2，CHEN Zuyu2，LIANG Xiangqian2，HUANG Xin1，ZHANG Xuedong2

2011, 30 (S2): -4128
Full Text:

[PDF 0 KB] (691)

+

Show Abstract

The explosion cratering effects in dry standard sands were investigated by using a 450 g-t geotechnical centrifuge apparatus. The ten centrifuge model tests were completed with a variety range of explosive mass，burial depth and centrifuge accelerations. Three methods were used to analyze the results of 10 centrifuge model tests of explosion cratering in sand. These three methods included Schmidt formula，Baker formula，and the correction Боресков formula. The first two formulas were derived by similarity analysis. The correctional Боресков formula was an empirical formula based on experimental data. The correlation coefficients R2 of the three methods were 0.931，0.960，and 0.998 respectively. A comparison of these three methods was also given in this paper. The Schmidt formula is the most suitable method for cratering effect analysis. The parameters of this formula can be accurately determined.

Select

SUPPORT OPTIMIZATION OF SOFT ROCK ROADWAYS BASED ON DAMAGE CONSTITUTIVE MODEL FOR WEAK INTERCALATED LAYERS

WU Guojun1，CHEN Weizhong1，2，YANG Jianping1，TAN Xianjun1

2011, 30 (S2): -4135
Full Text:

[PDF 0 KB] (681)

+

Show Abstract

Weak intercalated layers，to a large degree，affect the stability of rock mass when excavating roadways in underground engineering. According to analyzing the features of damage and separation-growing of weak intercalated layers，the exponential nonlinear damage evolution model of weak intercalated layers is proposed；and the contrast optimization of supporting is done for some roadway buried in deep mudstone with weak intercalated layers by finite element software ABAQUS. Aiming at the problem of floor heaving to a large deformation and a serious buckling deformation in the vicinity of weak intercalated layers at the initial period of roadway excavation，measures of prestressed anchor reinforcement，inverted arch excavation and backfilling and steel arch of shoring are proposed，which can restrain separation-growing or damage of weak intercalated layers and deformation of rock mass effectively. The research results can provide useful reference for some similar roadways in deep soft rock mass.

Select

SELECTION OF LIMIT EQUILIBRIUM METHODS IN THE DESIGN SPECIFITION FOR WASTE DUMP OF METAL MINE

LI Xiaochun1，REN Wei1，WANG Shaoquan2，WANG Haibin1，CUI Yinxiang1

2011, 30 (S2): -4142
Full Text:

[PDF 0 KB] (773)

+

Show Abstract

There are some controversies on the selection of stability calculation methods when preparing for the new specification of waste dump. We evaluate the accuracy and applicability of 7 limit equilibrium methods by using the difference percentage and standard deviation of safety factors in waste dump slope stability analysis. Combined with previous research，the application of limit equilibrium method in waste dump slope analysis is described. Ordinary method has a poor accuracy. The accuracy is larger than 30% and the standard deviation is large when dealing with ground water problem. Its calculation result can be used as a lower limit. Bishop method has an accuracy of 3.7% and good standard deviation，although only satisfying moment equilibrium. For the simple algorithm，it is recommended as a basic method. The correct values can be obtained from methods satisfying force and moment equilibrium，which applies to a variety of conditions.

Select

RESEARCH ON LAW OF MINING EARTHQUAKES IN A COAL MINE OF YANZHOU

TANG Zibo

2011, 30 (S2): -4152
Full Text:

[PDF 0 KB] (721)

+

Show Abstract

By using the observation data of mining earthquakes occurred from November 2004 to March 2009 in a coal mine of Yanzhou，Shandong province recorded by the seismic network，the sources of mining earthquakes are located and the following questions are studied：methods of improving the accuracy of mining earthquake source location；relationship between distribution of sources of mining shock and the tectonic background；relationship between large mining earthquakes and the in-situ ground stress；relationship between mining earthquakes and the process of mining；relationship between the mining shock and the disaster event that envelop wall is destroyed；the law of seismicity of mining earthquakes series. The primary results are obtained as follows：by using the methods of polarization analysis and wave form correlation analysis，the source location accuracy can be improved under the condition of sparse networks. The results show that it is the mining shock that made the top tray near the residual column of coal rake collapse and then formed strong blast that destroyed the envelope wall. It is also shown that the three component seismometer and wave form analysis have important effect in diagnosing the properties of mining disasters.

Select

BLASTING EXCAVATION AND VIBRATION EFFECTS OF SHALLOW TUNNEL EXCAVATION

GAO Wenxue1，YAN Pengcheng1，LI Zhixing2，WEI Pengwei1，HOU Binghui1

2011, 30 (S2): -4157
Full Text:

[PDF 0 KB] (746)

+

Show Abstract

Taking the project of Huolangyu tunnel in Mixing road as the background，the experiments for tunnel blasting excavation and ground vibration test are carried out. Based on the measurement of the waveforms of the vibration velocity in different distances away from the tunnel blasting sources on the ground，the vibration characteristic of the ground and its varying laws are studied. The results of the monitoring and analysis show that：(1) Along the tunnel excavation direction，the vibration velocity shows attenuation trend from the excavated zone to non-excavated. And the various law of shallow tunnel excavation blasting vibration is closely related with the cross-section size，depth，construction techniques and geological conditions，and so on. (2) The vibration control of wedge cutting holes blasting is the key of reducing or eliminating shallow tunnel vibrating calamity. And the choice of the multi-stage small wedge cutting holes instead of the big wedge cutting holes can noticeably ameliorate blasting vibration and rock fragmentation. (3) Comprehensive monitoring of the blasting vibration and optimizing blasting parameter can improve the blasting vibration harm and construction efficiency and reduce the consumption of materials and supplies at the same time.

Select

STUDY OF STRUCTURE EFFECT OF JOINTED ROCK MASS DEFORMATION MODULUS

ZHANG Zhanrong1，ZHAO Xinyi1，LIU Qinghui1，SHENG Qian2，YANG Yanshuang2

2011, 30 (S2): -4166
Full Text:

[PDF 0 KB] (704)

+

Show Abstract

According to the principle of equivalent deformation，the theoretical formula which can calculate the deformation modulus of jointed rock mass is derived. A new graphics called full space exhibition map is introduced，which can show the space distribution characteristics of parameters through the contour. Using the theoretical formula and full space exhibition map，a new method which can study the space distribution of the rock mass deformation modulus is formed. Using this method，the structure effect of jointed rock mass with one，two and three joint has been systematically researched. When the rock mass is cut by one joint set，the deformation modulus is the biggest in the direction which is parallel to the joint plane and presents as an extreme value line in the full space exhibition map，while the deformation modulus is the smallest in the direction which is vertical to the joint plane and present as an extreme value point in the full space exhibition map. When the rock mass is cut by two joint sets，the deformation modulus is the biggest in the direction of the intersection point of the two extreme value lines，while the deformation modulus is the smallest in the direction which is between the two extreme value points，in the full space exhibition map. When the rock mass is cut by three joint sets，the direction of the biggest deformation modulus is in the smallest triangle enclosed by the three extreme value lines，while the direction of the smallest deformation modulus is in the triangle enclosed by the three extreme value points，in the full space exhibition map. The weakened degree of deformation modulus becomes significant as the number of joint sets increasing. Because of the simple computational process and the obvious advantage of the space distribution characteristics，this method to evaluate the rock mass deformation modulus provides useful reference in the three dimensional full space.