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2008, 27 (S2): 3304-3304 doi:

[PDF] 227 KB (1110)

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STUDY ON WATER HOLDUP OF MUNICIPAL SOLID WASTE

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2008, 27 (S2): 3305-3305 doi:

[PDF] 214 KB (1153)

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A laboratory testing method，which is used to measure water holdup of municipal solid waste(MSW) is introduced. A artificial solid waste is used in the study，which is made according to the composition of a municipal solid waste landfill located in Southern China. In general，the dry gravimetric water holdup of the waste decreases with increasing of its dry density，the waste density is another important factor affecting water holdup. The volumetric water holdup for the dense waste also decreases with increasing overburden pressure and dry density. However，the volumetric water holdup for the loose waste initially increases with the increase of overburden pressure and dry density. After the volumetric water holdup reaches a maximum value，the volumetric water holdup then decreases with the increase of overburden pressure and dry density.

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DYNAMIC RESPONSE OF AN ELASTIC SLAB RESTING ON DOUBLE-LAYERED SUBGRADE SUBJECTED TO MOVING LOAD

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2008, 27 (S2): 3312-3312 doi:

[PDF] 288 KB (973)

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The dynamic response of a subgrade-slab system subjected to harmonic strip moving load is investigated using the Fourier transform and the inverse Fourier transform. The subgrade-slab interaction is considered，and the pavement is treated as orthotropic elastic slab resting on a double-layered subgrade. Taking the soil layer above the groundwater table as elastic single-phase layer and the soil layer below the groundwater table as saturated medium，the governing equations of subgrade-slab system are solved in the transformed field domains of moving space considering the finite depth of layers，and Lame decomposition theorem of displacement field and potential functions. Considering the mixed boundary condition at the upper surface，the fixed boundary condition at the lowest surface and that the stress and displacement at the interface of the layers are continuous；analytical solutions of vertical displacement，stress and pore water pressure in saturated layer are derived using the Fourier transform and the inverse Fourier transform. Numerical results are obtained by using the inverse fast Fourier transform(IFFT). Calculation results show that the vertical displacement of soil medium is considerably affected by the moving load velocity，frequency and the permeability of saturated layer. The influence of depth of elastic single-phase layer on vertical displacement depends on moving load velocity. The depth of elastic soil layer has great effect on pore water pressure in saturated layer，and the influence of the rigidity ratio between elastic single-phase layer and saturated layer on pore water pressure is similar to that of the depth of elastic soil.

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COUPLING EFFECTS OF INITIAL SHEAR STRESS AND LOADING RATE ON STRENGTH BEHAVIORS OF SATURATED SOFT CLAY

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2008, 27 (S2): 3321-3321 doi:

[PDF] 197 KB (1013)

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Undrained triaxial compressive tests are carried out on Hangzhou saturated soft clay to investigate the coupling effects of initial shear stress and loading rate on the monotonic characteristics of soft clay. It is observed that the shear strength decreases and the total strength increases as the initial shear stress increases. When the initial shear stress is 60 kPa，the shear strength decreases about 60%. The pore water pressure decreases with the increase of initial shear stress. When the initial shear stress is 60 kPa，the pore water pressure reduces about 50%. As the increase of loading rate，the strength increases and pore water pressure decreases. The stress-stain curve shows the strain-hardening characteristic without initial shear stress. However，it turns to be strain-softening with the increase of initial shear stress. Empirical equations for the peak strength and pore water pressure considering the coupling effects of initial shear stress and loading rate are proposed respectively by introducing the normalized peak shear stress parameter s and pore water pressure parameter . It is observed that with the increase of normalized strain rate，s increases and decreases. The relationships between s， and normalized strain rate show linearity with a semi-log scale. In such a case，the effect of initial shear stress on s and is not significant.

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THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS FOR EFFECTS OF STEP CONSTRUCTION ON DEEP SOFT SOIL FOUNDATION PITS

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2008, 27 (S2): 3328-3328 doi:

[PDF] 374 KB (1563)

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Time-space effects have been validated with a lot of soft soil deep foundation pits. Step construction during the excavation is an effective way for the application of the theory of time-space effect，though those applications are somewhat experiential. A method to analyze behaviors of deep foundation pits considering the effects of step-by-step construction is proposed. A 3D finite element program based on the model is developed. The method is used to analyze the deformations and inner forces in the retaining piles and the struts of a typical excavation case. The numerical results are compared with the results that not considering the construction effects. It is also proven that step construction is an effective way to control displacement of deep foundation pits in soft soil. Finally，the method proposed here is used to analyze an actual deep pit project in Hangzhou. The analytical results are compared with the measured data. It is indicated that the suggested method can be well used to simulate the complex excavation process of foundation pits.

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STUDY ON STABILITY ANALYSIS METHOD FOR MORAINE SOIL SLOPE IN WEST WALL OF TAIHE IRON MINE

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2008, 27 (S2): 3335-3335 doi:

[PDF] 342 KB (1223)

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Aiming at the moraine soil slope in west wall of Taihe Iron Mine，a method based on the results of in-situ test and laboratory test for moraine soil which couples automata(CA) with FLAC3D to conduct triaxial simulation test is presented and shear strength model for moraine soil is established. Firstly，CA is adopted to simulate the microstructure of moraine soil and specimens are prepared for triaxial simulation test. Secondly，the simulation procedures of specimens are introduced into FLAC3D and then simulation tests are conducted. Finally，after the data from simulation results are processed，the probability models for shear strength are obtained. After that，a comprehensive analysis method of slope stability which integrates numerical analysis method，limit equilibrium method and reliability analysis method，is presented. In the comprehensive analysis method，three methods are linked to each other by adopting strength reduction technique，simplified first-order second-moment method and Rosenblueth method. The results of the three cases are interrelated consequently. According to the research results mentioned above，a multi-angle stability analysis of the moraine soil slope is made. The analyses of displacement vector and deformation indicate that the failure mode of the slope mainly exists as shallow circular shear failure. Although the mean factor of safety is high(1.40–1.59)，the probability of failure(1.07%–3.36%) is high due to the higher uncertainty of shear strength parameters. As a result，the risk level of this slope is unacceptable so that some effective measures should be adopted.

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APPLICATION OF REDUCED SUCTION TO EARTH PRESSURE CALCULATION OF UNSATURATED SOILS AND SWELL INCREMENT

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2008, 27 (S2): 3341-3341 doi:

[PDF] 234 KB (954)

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A method of determination of reduced suction based on the principle of equivalence of deformation is introduced；and the reduced suction is used as an essential variable in the earth pressure calculation of unsaturated soils on retaining wall and swell increment. The rest soil pressure，active soil pressure，passive soil pressure of unsaturated soil under different water table conditions，and swell increment of unsaturated soil under different water level conditions and swell increment that are caused by rainfall have been considered. The calculation results have rationally reflected the distribution trend of unsaturated soil pressure and swell increment. Comparing the calculation results with the results of centrifugal model test and the model trough test，it is found that they have very good consistency. Calculation results also verify the proposed formulation.

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FIELD TEST ON TIME EFFECT OF BEARING CAPACITY ON END-OPEN PILE AND END-CLOSED PILE

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2008, 27 (S2): 3349-3349 doi:

[PDF] 155 KB (1491)

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LIMIT EARTH PRESSURE UNDER PLANE STRAIN CONDITION

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2008, 27 (S2): 3354-3354 doi:

[PDF] 170 KB (1260)

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Based on the strength criterion under plane strain condition and Rankine¢s theory，a simplified method for determination of limit earth pressure is proposed. The principal stress in the plane strain direction，which can be determined under the rigidity-plasticity assumption using static earth pressure coefficient，is the intermediate principal stress under the limit equilibrium condition. The relationship between major and minor principal stresses is obtained based on the strength criterion. Then the earth pressure coefficient can be determined. Although the proposed method is as simple as that of the Rankine¢s theory，it can obtain more reasonable calculation results，and accordingly improve the design methodology yielding output more economically. The results also show that the difference between the proposed method and the Rankine¢s theory is enlarged along with the increase of the friction angle of the material. The validity of this method is confirmed by observed data from the practical foundation engineering. Compared with the Rankine¢s theory，the proposed method can be more rationally used in soil-retaining structure designing.

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EXPERIMENTAL RESEARCH ON DEFORMATION AND STABILITY OF SHALLOW-BURIED LARGE-SPAN SOIL-LAYERED TUNNEL

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2008, 27 (S2): 3360-3360 doi:

[PDF] 433 KB (1306)

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The characteristics of two kinds of silty clays in shallow-buried large-span soil-layered tunnel，which are soft-plastic and hard-plastic soils，are studied using centrifugal model test；and the main deformation characteristics are discussed through the unconfined compression strength，rebound and arching capabilities. The effect on construction stability is also analyzed. By contrast of unsupported tunnel excavation with different soil covers，the great difference between soil and rock tunnels in arching is found，and the hard-plastic soil has arching ability while the soft-soil does not have. It is shown from the deformation characteristics that there isn¢t relaxed earth pressure in shallow clay but deformation pressure，then the load on the tunnel can be determined according to the deformation. Besides，the influence of soft-plastic interlayer with different locations to excavation deformation and construction stability is studied. It is found that the soft-plastic interlayer has a large effect on the excavation stability，especially for the interlayer at the crown. The layered horizontal and vertical deformations of soil with different covers are measured. Thus，whether the shear band exits or not，the deformation characteristics inside the shear band are analyzed.

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ANALYSIS OF MOISTURE TRANSPORT IN AN EVAPOTRANSPIRATION COVER

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2008, 27 (S2): 3367-3367 doi:

[PDF] 265 KB (1095)

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Based on the general principles included in the performance of an evapotranspiration cover，the plant interception，the soil evaporation，the evapotranspiration，runoff，and the net infiltration are calculated considering Penman¢s potential evapotranspiration. The calculated net infiltration is input into an unsaturated flow model as a boundary condition to simulate the moisture transport and evaluate the performance of an evapotranspiration(ET) cover. The analytical results show that evapotranspiration is crucial to the moisture transport. Water contents of soils in the upper portion are sensitive to the variation of rainfall and evapotranspiration，whereas water contents of soils in the bottom remain almost remain unchanged. The storage and release of infiltrated water happen mainly within the root depth. A 120 cm thick ET cover with a good stand of plants and a root depth of 50 cm can satisfy the design requirement. The ET cover has an advantage over conventional landfill covers in reducing rainfall percolation.

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ANALYSIS OF DEFORMATIONS OF SHALLOW-BURIED REINFORCED CONCRETE STRUCTURES AND DYNAMIC EARTH PRESSURES IN LIQUEFIABLE SOILS

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2008, 27 (S2): 3374-3374 doi:

[PDF] 284 KB (1025)

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Based on the method of effective stress analysis using a multiple shear plasticity model and the concept of liquefaction front，numerical modeling for deformations and dynamic earth pressures acting on the shallow duct-type reinforced concrete(RC) structures subjected to earthquake motions is presented. Moreover，the change rules of the relative displacement between the underground structures and liquefiable soils，dynamic earth pressures acting on the sidewall of RC structures，shear stress and excess pore water pressures in liquefiable soil during earthquake for the cases with a crest input motion of 0.85 g are further investigated. The results indicate that the values of deformations and bending moments，curvatures of RC structures increase with the level of input motions. And plastic yield area firstly occurs on the corners of structure and expands to other areas. The interaction factors in liquefied models with strong motions are less than those of non-liquefied models with a motion of 0.1 g. The values of relative displacement between ground and structure increase sharply up to a stable value after the soil is liquefied during earthquakes. The maximum and residual values of dynamic earth pressures acting on sidewalls increase with shaking. However，the growth is not a simple linear relationship with the input motion. On the contrary，the shear stresses acting on the top and the bottom slab，and the horizontal effective stresses acting on sidewall decrease sharply when the soil is liquefied. These results provide the foundation and references for the seismic design of shallow underground structures in the liquefiable soils.

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STUDY ON REINFORCEMENT OF EARTHEN SITES BY BAMBOO-STEEL COMPOSITE ANCHOR

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2008, 27 (S2): 3381-3381 doi:

[PDF] 193 KB (1224)

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The bamboo-steel composite anchor is a kind of new anchor that is designed for aiming at the bulk earthen sites. According to the test，the reinforcement of earthen sites accords with the principle of the heritage sites protection by adopting the PS series of grout material and the bamboo-steel composite anchor. If adopting the cement mortar as grout material，its anchoring unit power can be adopted 30 kN/m；if adopting the PS-(F+C) as grout material，its anchoring unit power can be adopted 20 kN/m. When reinforcing the earthen sites by the bamboo-steel composite anchor，its weak interface exists between anchor body and anchoring solid. The strengths of cement-mortar and PS-F slurry are adopted for anchoring by the bamboo-steel composite anchor. The standard value of cohesive strength averages 187 kPa，the eigenvalue averages 85 kPa between the cement-mortar and anchor body. The standard value of cohesive strength averages 114 kPa，the eigenvalue averages 52 kPa between the 12% PS-F and anchor body.

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ANALYSIS OF RETAINING STRUCTURES FOR DEEP FOUNDATION PIT
OF QIUTAO ROAD STATION IN HANGZHOU METRO

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2008, 27 (S2): 3386-3386 doi:

[PDF] 235 KB (1495)

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The retaining structure deformation of the deep foundation pit is an important factor for the effect on the deformation of deep foundation pit. In view of the retaining structure of deep foundation pit for Qiutao Road Station in Hangzhou Metro，the finite element method of elastic foundation beam bar system is adopted. Firstly，the computation analysis to the standard section as a project example of the deep foundation pit is carried out through the contrastive analysis of the computed results and measured data，and then the computation model and the computation method are confirmed. Finally，in view of the silty sand soil stratum of the Qiutao Road Station， the rigidity of the retaining structure，the order of the excavating and the supporting of the deep foundation pit，the arrangement mode of the supports，and the improvement soils depth and other design and construction factors on effect of the deformation and internal force of the retaining structure are all discussed. The analytical results indicates that the pile intensity satisfies the requirements，usually it is not suitable through increasing the pile rigidity to reduce the deformation of the retaining structure. For the multi-support arrangement，the way that the supports are dense in the excavation upside and the supports are sparse in the excavation lower part is optimized. In the construction，the first supporting and then excavating excavation way should be adopted. There is a critical depth for the improvement soils. The appraisal analysis to each influencing factor is adopted to provide the reference to the related design and the construction.

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STUDY ON SHIELD TUNNEL DEFORMATION DUE TO FOUNDATION PIT CONSTRUCTION

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2008, 27 (S2): 3393-3393 doi:

[PDF] 285 KB (1265)

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NUMERICAL ANALYSIS OF EARTH PRESSURE BALANCE SHIELD TUNNELING AT GUOMAO—SHUANGJING INTERZONE OF BEIJING SUBWAY LINE NO.10

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2008, 27 (S2): 3401-3401 doi:

[PDF] 407 KB (1328)

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Shield tunneling process is simulated with FLAD3D combined with engineering situation of Guomao— Shuangjing interzone of Beijing subway line No.10. Stress and displacement monitoring points are distributed around the model shield tunnel. Regularities of displacement and stress in surrounding soil are studied. The main results are as follows：(1) not only vertical but also horizontal displacements show that soil is extruded ahead of excavation；(2) vertical displacement is more prominent that horizontal displacement；(3) vertical and horizontal stresses decrease speedily near the tunneling excavation face with half stress being released；and (4) a mass of disturbance mainly occurs in 20 m between excavation face and its behind. It is found that the simulated results are in good agreement with in-situ values.

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NUMERICAL STUDY OF BEARING CAPACITY FACTORS FOR STRIP FOOTING EMBEDDED IN HOMOGENEOUS SUBSOIL

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2008, 27 (S2): 3408-3408 doi:

[PDF] 246 KB (1329)

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In engineering practice，the limit bearing capacity of foundations is usually estimated using the superposed formulae suggested by K. Terzaghi. As it is used for strip footing embedded in homogeneous subsoil，the bearing capacity factors and the pertaining embedment modifying factors must be determined. Many published papers have used limit equilibrium method，slip-line method and upper bound method to investigate these factors. However，the predicted bearing capacity is affected by the assumed failure mode，which will lead to bigger discrepancies in the value of these factors obtained by different investigators. Conversely，the finite element method can predict more accurately bearing capacity without assuming failure mode in advance. An elastoplastic numerical model for embedded strip foundation is established by introducing zero-thickness interface element to remove the computational difficulty of the footing corner in finite element analysis and simulate the contact between subsoil and footing. A numerous numerical analysis for three types of subsoil，i.e. undrained clay，sand and the soil with nonzero cohesion and frictional angle，is executed to obtain the bearing capacity factors and embedment modifying factors. These factors are presented and compared with published results. Some rules of these factors varying with roughness of footing sides，embedment，surcharge load，soil strength are summarized and the applicability of these factors is also determined. These results can provide references to foundation design.

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BEHAVIORS OF SOCKETED H-SHAPED STEEL PILES

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2008, 27 (S2): 3416-3416 doi:

[PDF] 277 KB (3471)

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A series of filed load tests and laboratory tests are conducted to investigate the pile deformation and the load transfer behavior of socketed H-shaped steel piles. The instrumented test results reveal that significant shaft resistance can be mobilized along the steel-grout interface. On the other hand，the H-shapes steel pile and the grout body cannot be assumed as a composite body in the evaluation of pile deformation. Laboratory bond tests are carried out on H-shaped steel/grout pile specimens. The bond test results indicat that the lateral confinement can significantly improve the bond strength along the steel-grout interface. Furthermore，if lateral confinement is provided，the welded steel studs can also improve the bond strength. Therefore，the steel-grout bond strength is not a constant along the depth in a socketed H-shaped steel pile. The comparison between the laboratory and the field test results demonstrate that slippage can occur along the steel-grout interface in the load tests. For short piles，the slippage can develop along the whole length above the socket section. For longer piles，slippage is likely to develop to a certain depth above the socket section. Such behaviors should be considered in the evaluation of the pile deformation under the vertical load. A modified calculation method for pile deformation is suggested. The pile deformation evaluated from the suggested method is closer to the field measured data than that the one from the local guidelines. In addition，more detailed analyses can be carried out for load test results by using the suggested method.

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UPPER BOUND APPROACH OF RIGID ELEMENTS FOR INHOMOGENEOUS SOIL SLOPE STABILITY ANALYSIS

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2008, 27 (S2): 3425-3425 doi:

[PDF] 261 KB (1271)

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Stability analysis of inhomogeneous soil slope is one of classical problems for soil mechanics. The authors establish a rotational failure mechanism with combination of different logarithmic spiral arcs based on the theory of limit analysis method. When slip mass is looked upon as rigid-body，the layered soil slope can be discretized and meshed by triangle elements which are the pre-processor of the ANSYS software. According to upper bound theory of limit analysis method，not only every triangle element¢s external work-rate done by self-weight and seismic force but also the internal energy dissipation produced in different logarithmic spiral arcs can be totally calculated. By means of strength reduction method and virtual work-rate equation for upper bound theorem，the calculation formula of upper bound solution with rigid elements for inhomogeneous soil slope stability analysis can be deduced. As an example of two layered soil slope，the factor of safety is computed by different methods such as Sweden slice method，Bishop method，Janbu method and upper bound approach of rigid elements. The results show that the new method can obtain the upper-bound solution for layered soil slope，but the value of factor of safety calculated by the method of Bishop is close to the lower-bound solution. It is very important to choose proper solution of factor of safety when the upper limit and lower limits are certainly made. At last，the new method has good applicability for layered soil slope stability analysis.

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DYNAMIC MONITORING AND NUMERICAL ANALYSIS OF SOIL-LIKE CUT SLOPE

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2008, 27 (S2): 3431-3431 doi:

[PDF] 631 KB (1232)

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Based on a case of soil-like cut slope in Zhangjiakou－Shijiazhuang Expressway，local monitoring combined with numerical simulation is adopted in the slope stability analysis. Firstly，according to the in-situ information about layers of earth distribution and thickness of landslide，displacement monitoring points are set up. There are two parts of monitoring system：one is inclinometer to monitor slope¢s deep part displacement，another is level instrument combined with theodolite to monitor slope¢s surface displacement. Monitoring result displays that after mini-typed steel tube grouting，the soil¢s properties are changed，and the displacement of slope approaches to critical sliding value of after excavation once again. The first time sliding is simulated by particle flow code(PFC). Based on the same model after sliding and through recovering parallel bond among particles which are near the sliding surface，the effect of grouting is simulated，and then excavation. Monitoring points in the model show that the displacements show progressive change，and expand to failure finally，demonstrating that slope reaches limit equilibrium state again. It means that measures should be taken in time. Finally，rectangle anti-sliding pile combined with low retaining wall in the toe of slope is adopted to reinforce the slope，which is proven to be rational. Local monitoring combined with numerical simulation analysis method is qualified for dynamic analysis，and it can predict the slope¢s trend pattern in time，which can be applied to middle and mini-scale slope¢s analysis widely.

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DEVELOPMENT OF A NEW-TYPE APPARATUS FOR MEASURING SEEPAGE DEFORMATION

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2008, 27 (S2): 3441-3441 doi:

[PDF] 177 KB (1269)

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In view of the defects of the existing apparatus for measuring seepage deformation such as poor seal，seepage areas decreased by sample fix installation，complication of apparatus，etc，a new type of apparatus that can be used to measure the seepage characteristic of cohesive soil and cement soil is developed based on the analysis of the characteristic and testing theory of seepage deformation of soil. The apparatus has some unique designs such as adopting flexible seal method in which the samples are wrap by rubber membrane with confining pressure，and a ring porous stone is used on the top of the specimen to fix it，etc.. The apparatus can be used to measure seepage coefficient and deformation，and it can guarantee the effective seepage area of specimen in test and permit the test specimen to produce seepage deformation at the same time，and the seal quality of apparatus is good under the seepage hydraulic pressure in the test. The practical application indicates that the seepage coefficient and deformation and the ratio of resistance seepage slope of soil obtained by the proposed apparatus have high reliability and precision.

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STUDY ON MECHANICAL CHARACTERISTICS OF SHRUB
ROOTS FOR SLOPE PROTECTION IN LOESS AREA OF
TIBETAN PLATEAU

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2008, 27 (S2): 3445-3445 doi:

[PDF] 334 KB (1661)

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The single root tensile and shear tests were carried out to study the mechanism of slope protection by shrub roots and analyze the mechanical characteristics of shrub roots on Caragana korshinskii，Nitraria tangutorum，Zygophyllum xanthoxylon and atriplex canescens in loess area of Tibetan plateau where Xining basin was taken as an example. Experiments and studies showed that power or exponential relations existed between single root tensile resistance and root diameter of four shrub roots，and both the single root tensile resistance and shear resistance increased with increasing diameter，and the increment rate of Atriplex canescens is the largest，followed by Caragana korshinskii、Zygophyllum xanthoxylon and Nitraria tangutorum for eighteen-month age shrub. Either power or exponential relations were fitted between root tensile strength and root diameter，and the root tensile strength decreased with increasing diameter. The results revealed that various root structures have different tensile stress-strain characteristics. The stress-strain curves of four shrub roots also presented straight line relation in root initial stage after tension. As the pulling force kept increasing after loading over elastic limit，the stress-strain curves reflected the non-linear elastic characteristics. The rate of tensile elongation of four shrub roots was all over 13%，and the elongation rate of roots decreased with increasing diameter. The shallow soil of studied area from 0.3 m to 0.8 m with plenty of hair roots had strong single root tensile strength，shear strength and non-deformability，so the shallow soil played an important role in controlling soil and water loss of slope，reinforcing shear strength of soil-root composite and controlling slide deformation. According to the root mechanical characteristics and root morphological features，Atriplex canescens and Caragana korshinskii had significant function in slope protection in of loess area Tibetan.

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EXPERIMENTAL STUDY ON RELATIONSHIP BETWEEN TENSILE AND SHEAR STRENGTH OF UNSATURATION CLAY EARTH MATERIAL

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2008, 27 (S2): 3453-3453 doi:

[PDF] 210 KB (2267)

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In order to find out the qualitative and quantitative relationships between triaxial tensile strength and triaxial shear strength，contrast experiments are carried out including triaxial tensile，triaxial shear and uniaxial tensile with remolded samples of unsaturated clay in core wall of Heihe Dam in Xi¢an，Shannxi province under different moisture contents. The experimental results show that：(1) the shear intensity index of unsaturated clay c and j decrease with the increasing of moisture contents；(2) though triaxial or uniaxial experiments of unsaturated clay，the Mohr circle，which is decided by confining pressure as major principal stress and axial stress as minor principal stress，accords with Coulomb criterion；and (3) there is functional relationship between tensile strength and shear strength of different unsaturated clay samples with same physical nature. Based on these conclusions，tensile strength of unsaturated clay can be estimated through results of shear tests without tensile strength test conditions.

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STUDY ON REFUSAL OF RESTARTING OF LARGE DIAMETER AND DEEP PENETRATION PILE AND BEARING CAPACITY CALCULATION

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2008, 27 (S2): 3459-3459 doi:

[PDF] 247 KB (1853)

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Due to the harsh environmental conditions in ocean engineering，intermissions occur during the driving of large diameter and deep penetration piles，which may cause difficulties，even refusal，in re-starting the pile. Analytical results show that soil strength recovering is influenced by the soil stratum distribution，the crack development around the pile，the cessation time of driving and the soil plug effect in the pile pipe. A calculation method is proposed to identify the developed excess pore water pressure and its time effects in the soil around the pile during driving. Based on the driving records，the back-figured method is applied to estimate the pile bearing capacity after refusal taking place. The calculated results agree well with the in-situ observed data，which indicates that the proposed back-figured procedure can be used in similar pile driving situations.

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NUMERICAL ANALYSIS OF SCALE EFFECT OF PILE-BUCKET FOUNDATION STRUCTURES UNDER UPLIFT LOADING

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2008, 27 (S2): 3465-3465 doi:

[PDF] 233 KB (1223)

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The ABAQUS software was used to research the uplift loading and the affected region of ground soil body on pile-bucket foundations of different sizes under same uplift displacement，and preliminary design of pile-bucket foundation was carried out. The sizes of pile-bucket foundation mainly included the pile length under the top of the bucket(L3)，the bucket radius(R) and the bucket wall height(H). The ultimate uplift loading of pile-bucket foundations are various with change of size of foundations. The scope influenced by the uplift bearing capacity of foundation and ground soil body could be highly enhanced if L3，R and H were increased; the influence of change R was most to the uplift bearing capacity of foundation and the ground soil body horizontal scope，and the change of L3 took the second place，and the change of H went the last；the influence of change L3 was most to the ground soil body longitudinal scope，and followed by the change of H and R. When the proportion relation of L3 and R reached 8.0∶1.0，common uplift performance of the pile structure and the bucket structure together could be fully manifest; when the proportion relation of R and H was 0.6∶1.0，the uplift performance of the bucket structure was embodied completely.

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STUDY ON STRENGTH REDUCTION FEM CONSIDERING
SEEPAGE AND BOLT

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2008, 27 (S2): 3471-3471 doi:

[PDF] 356 KB (1306)

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Due to the limitation of the numerical models of rock bolt by finite element method(FEM) in geotechnical engineering at present，the bolt model suitable for the FEM of strength reduction method and optimization of anchor parameters is exploited. The program of the 3D FEM considering seepage and the action of bolt is developed，in which the failure model of bolt because of lowness of cohesion between the bolt and the soil around can be considered as well. Through comparison of the calculation of FEM and limit equilibrium method，the applicability of FEM to analyze the slope stability is evaluated. The comparison result shows that the finite element method is feasible to analyze the stability of the slope considering seepage and strength reduction caused by seepage and the action of bolt.

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EXPERIMENTAL STUDY ON MUDSTONE¢S CREEP BEHAVIOR UNDER DIFFERENT WATER CONTENTS AND ITS EFFECT ON CASING DAMAGE

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2008, 27 (S2): 3477-3477 doi:

[PDF] 271 KB (1536)

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Strength and creep experiments of mudstone from Daqing Oil Field under different saturated conditions are performed through the XTR01 servo-controlled compression machine. The creep characteristics and the change of mechanical parameters with the increment of water content are analyzed. The results indicate that the rock strength and elastic modulus decrease with the increment of water content，while the creep strain and steady state creep strain rate increase. Through the experiments，the nonlinear creeping constitutive equation of mudstone considering the change of water content is established as compared with the creep characteristic curves. In water injection reservoir，based on the relationship between the water cut in the mudstone and the mechanical property of the mudstone，the mechanism of casing failure is analyzed，and the casing-cement sheath-mudstone creeping model is built in order to simulate the creep pressure of mudstone with different water contents. The simulation results show that under heterogeneous stress，the increasing water content accelerates the incremental rate of the creep pressure of mudstone，so the time of reaching yield state reduces significantly，which means service time of case becomes much shorter. During the process of water injection production，high injection pressure cut in mudstone should be prevented to reduce casing damage.

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ANALYSIS OF RE-FRACTURE PROPERTIES OF CRACKED ROCK MASS UNDER HOOP EFFECTIVE CONSTRAINT

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2008, 27 (S2): 3483-3483 doi:

[PDF] 280 KB (896)

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The underground rock after failure forms cracked rock mass in a certain area，which represents great structural effect under effective support，namely，it has the capacity of load-carrying and resisting deformation. During the process of resisting the outer load or deformation，the cracked rock mass shows the stress hardening characteristic. Under outer-loading，the rock blocks within the cracked rock mass produce re-fracture and the degradation of rock mechanical behavior. The evolution of stress state and mechanical behavior of cracked rock mass when bearing outer load are determined by the integral mechanical performance of cracked rock mass，the stress state of hoop constraint and the characteristics of initial failure surface. When re-loaded on cracked rock mass，both the direction and magnitude of principal stress on the failure surface change gradually and the direction of principal stress on failure surface is different from that of rock mass，by which the new failure surfaces form and develop sequentially. This research reflects the load-carrying properties and re-fracturing process of cracked rock mass，which is very significant for study of stability of deep underground engineering.

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DISCUSSION ON GENERAL RELATIONSHIP BETWEEN PLASTIC FACTOR AND PLASTIC TIME

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2008, 27 (S2): 3490-3490 doi:

[PDF] 284 KB (954)

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It is difficult to determine the expression of an intrinsic time for a specific material in the endochronic theory of plasticity. Meantime，according to the definition of the intrinsic time by K.C. Valanis，the relationship between the increment theory of plasticity and the endochronic theory of plasticity becomes ambiguous. In order to overcome the limitations above，the new intrinsic time，which is named plastic time，is defined. The old intrinsic time is a special case of the plastic time. According to the definition of plastic time，it is illustrated that the increment theory of plasticity is a special case of endochronic theory of plasticity. It is proved that the plastic factor in the increment theory of plasticity belongs to the plastic time. The expression of plastic time could be derived from the expression of plastic factor. It has been shown by mechanic tests that the plastic factors are different from material. As a result，the plastic time is not identical for different materials. A lot of instances present the specific method to deduce the expression of a finite plastic time and provide the generalized approach to derive the integral endochronic constitute equations from the increment theory of plasticity by means of the plastic time and the impulse function.

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MODEL OF RANDOM POROUS ROCK AND WAVE FIELD
ANALYSIS IN 2D SPACE

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2008, 27 (S2): 3498-3498 doi:

[PDF] 204 KB (1079)

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A new heterogeneous constitutive model of random porous rock is established by introducing two model parameters：the local radius(r) and the local porous density(p). In this model，the local radius(r) and the local porous density(p) are used to describe the length of the porous medium and the local porous space density in each distributed porous zone respectively. The elastic properties of rocks containing a random spatial distribution of porous size can be simulated by this model with the connection of the macro-mechanical properties(the elastic wave speeds) of the porous rocks and the model parameters(r and p). Numerical example indicates that the real heterogeneous medium can be modeled effectively as long as appropriate model parameters are given. Different heterogeneous random porous rocks have different scattering effects on wave speeds. The elastic wave speeds caused by larger pore are more distinguishable. The relative random distribution characteristics of pores hardly affect wave speeds under the same random distribution of the local porous density and local radius. The resolving power of S-wave on random porous rock is stronger than that of P-wave，and S-wave is more sensitive to anisotropy caused by micro-cracks.

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A NEW METHOD FOR ESTIMATING ROCK JOINT SIZE

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2008, 27 (S2): 3503-3503 doi:

[PDF] 246 KB (972)

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The joint size is the extension of the joint plane in space. For the joint Poisson disc model，the joint size can be represented by the disc diameter. Warburton¢s method is right theoretically，but not practical in determining the joint probabilistic distribution. A new method for estimating the joint diameter distribution is proposed without using the joint probabilistic distribution. With the variation of the initial mean values of the joint diameter，the relative errors between the initial mean values and the calculated values by the numerical method can be acquired. The relationship between the relative errors and the initial mean values is analyzed. When the error is zero，the optimal joint diameter is obtained by numerical method，and so is the joint diameter distribution. To verify the numerical method，two kinds of theoretical joint diameter distributions are adopted：negative exponential and lognormal distributions. The errors between the theoretical joint diameter and the calculated joint diameter by the numerical method are very small. The theoretical joint diameter distribution and the joint diameter distribution by the numerical method are uniform. The parameter analysis is implemented to determinate the available condition of the numerical method. Especially，the accuracy by the numerical method is better when the mean value of the joint diameter is relatively large and standard deviation is small. From the results above，it is concluded that the numerical method for calculating the joint diameter distribution is simple，valid and accurate. The numerical method is used to analyze the joint data of the statistical homogeneous domain II of the Jiji quarry-the preselected area in Beishan area，Gansu Province for Chinese high-level radioactive waste repository. The diameter distribution is acquired by using trace distribution from the multi-circular window sampling method.

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EXPERIMENTAL STUDY ON GAS SLIPPAGE EFFECTS IN HYPOTONIC COAL RESERVOIR

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2008, 27 (S2): 3509-3509 doi:

[PDF] 221 KB (1284)

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Under the depth of about 1 000 m in the deep mining，the pressure of the coal-bed is considerably high and the permeability of the coal-bed is low，in which the porous media are regarded to be highly compacted. Considering the percolation in this pre-pressing porous media，the slippage effects are remarkable，which will increase coal reservoir penetration function. So the experimental methodology is adopted to study the coal samples in Jilin and Fuxin City in order to explore the influence of slippage effects considering confining and pore water pressure，and to analyze the influence of slippage on the gas permeability under different confining and pore water pressures，and to find the range of confining pressure of beneficial influence of slippage on the gas log permeability of different hypotonic reservoirs. It verifies the universal existence of low permeability coal gas slippage effect. The experimental results establish the foundation of understanding the internal structure of coal and coal-bed methane slippage flow in coal seams and present significant theoretical value for carrying out coal-bed methane industrialization in hypotonic reservoirs.

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STUDY ON CREEP PROPERTY OF GLAUBERITE SALT ROCK

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2008, 27 (S2): 3516-3516 doi:

[PDF] 176 KB (1137)

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In nature，the pure glauberite appears in the form of compound with structural formula of Na2Ca(SO4)2，but in the sample it appears in the form of mixture by glauberite and claystone internally，which determines that its mechanical and creep properties are different from those of general salt rock. Uniaxial compression creep test over 100 days is carried out under different stress levels. It is found that the creep velocity under high stress level is larger than that under low stress level，and the creep velocity and creep deformation are lower than those of general rock salt. By regressive analyses，the creep curve equations of glauberite salt rock under different stress levels are obtained，and creep constitutive relation of glauberite rock salt by comparing the creep curves with the theoretical curves is discussed. It is found that the Nishihara model containing viscoelasto plastic unit can better reflect the glauberite creep rule，and the correlation parameters are fitted as well.

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COMPARATIVE ANALYSIS OF ACOUSTICS EMISSION CHARACTERISTICS ON DAMAGE AND DEFORMATION OF COAL SAMPLES UNDER DIFFERENT LOADING MODES

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2008, 27 (S2): 3521-3521 doi:

[PDF] 381 KB (1125)

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Deformations and damages of coal have intrinsic relativity with dynamic destabilization. The experiment on large size coal progressive fracture is a fundamental way to analyze the crack and evolution process of surrounding rock in the mined-out area. By in-situ comprehensive investigation and the well-chosen coal specimens of different sizes from the Western Huating Coal Mine where serious mining-induced seismicity occurs，based on the uniaxial test of some columnar and simple coal specimens，the acoustic emission(AE) characteristic experiments of two cube specimens of large size with different structures and heterogeneity(parallel and vertical lamination，the dimensions are 195.0 mm×110.0 mm×206 mm，195.0 mm×195.0 mm×11.5 mm respectively)，are conducted under different loading models，and abundant information and parameters upon deformation and their evolution are acquired. The corresponding statistical physical parameter(state vector)，which characterizes the continuous rough particle and spatial field is adopted in order to describe cracks and damages process of the coal media and their damage degree quantitatively. Furthermore，the damage degree percent is proposed as a quantitative index to characterize local damage and concentration of fractures. Finally，the comparative analysis between stress-strain and AE progressive characteristics are obtained. An essential qualification is provided to theoretical analysis，numerical simulation so as to enhance the accuracy of temporal-spatial-relationship and intensity of dynamical unstable and safe mining prediction.

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STUDY ON INFLUENCE OF BOUNDARY CONDITIONS ON RESULTS OF FOUR POINT SHEAR CONCRETE SPEKLES EXPERIMENTS

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2008, 27 (S2): 3528-3528 doi:

[PDF] 508 KB (1159)

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Several tests are conducted in which the concrete specimens are divided into two groups：the single-edge notched(SEN) and the double-edge notched(DEN) concrete beams. Both of the two groups of specimens are loaded under four point shear force and two different types of boundary conditions. The whole failure process of the specimens is shot with charge coupled device(CCD). From the speckle images，different failure phenomena are seen induding the propagation paths of cracks and final failure mode. The speckle images shot by the CCD are manipulated from which the displacement，strain and shear fields in strain horizontal and vertical directions in the surface of specimens are gained. Among the speckle images，some are picked out at certain intervals and compared with that before deformation in order to obtain diseplacement and strain fields. The evolution process of each field is gained by arrangind those fields to the time order. Comparing the displacement and strain fields gained at the place where the cracks start，it is shown that the magnitude of the horizontal and vertical displacements are close，and the values of the horizontal and vertical strains are in the same grade. The results demonstrate that the shear stress is not dominant in the zone near the notches. It also indicates that，though the sliding support is adopted，friction in the support is not reduced to a certain extend. Therefore the support should be treated carefully so as to get better results from four point shear test.

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EXPERIMENTAL STUDY ON PERMEABILITY-EFFECTIVE-STRESS LAW IN LOW-PERMEABILITY SANDSTONE RESERVOIR

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2008, 27 (S2): 3535-3535 doi:

[PDF] 279 KB (1464)

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The experiments included many cycles from which the pore fluid pressures were different. Each cycle run under constant pore fluid pressure by increasing or decreasing confining pressure. Experimental data were dealt with by steady state method，and analyzed with response-surface method. It was found that the effect stress coefficient a varied with pore fluid pressure and confining pressure. At the higher confining pressures in the test，all of the coefficient a were below 0.11，which was contrary to conventional view. In order to analyze the stress-sensitivity of low-permeability sandstone sample，coefficient a = 1.0 and coefficient a obtained from the experiment were adopted. It was shown that permeability stress sensitivity was very strong as conventional a = 1.0 was used while hardly existed as the effective-stress coefficient a adopted from the experiment was used。

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STUDY ON GEOMETRICAL PROPERTIES OF FRACTURE APPEARANCE IN GYPSUM BRECCIA BASED ON 3D GIS STATISTIC

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2008, 27 (S2): 3541-3541 doi:

[PDF] 215 KB (1119)

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By employing 3D laser scanning system，precise measurements of topography on fracture appearance in gypsum breccia under uniaxial compression are taken from which the fracture surface is visualized by using GIS technique. 3D parameters of the geometrical properties，such as asperity height and slope of rough surface are analyzed. The distribution of geometrical properties and its variation with increase of water content are analyzed according to frequency distribution of the histogram. At last，the fractal characteristics of fracture appearance under different water contents are studied. Therefore，the fracture dimensions of appearance under different loading directions and the variation with the increase of water contents are deduced. The test results show that the distributions of asperity height and slope match the normal distribution approximately，and the average of asperity height increases with the increase of water content linearly while the average of slope decreases with the increase of water content linearly. The fractal dimensions of appearance under different loading directions are correlative with water content；as a result，fractal dimension can be one of the important parameters to describe fracture appearance quantitatively. Based on the testing analysis of laser scanning of fracture appearance in gypsum breccia，there are close connections between fractal dimensions of the geometrical properties of fracture appearance and water content under uniaxial compression. The process and mechanics of fracture appearance under uniaxial compression are given as reliable testing basis to further analyze the process of damage evolution and failure mechanism of gypsum breccia.

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DETERMINATION METHOD OF SHEAR STRENGTH BASED ON CLASSIFICATION OF ROCK STRUCTURE SURFACE

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2008, 27 (S2): 3547-3547 doi:

[PDF] 182 KB (1724)

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RESEARCH PROGRESS OF EXPLOSION-RESISTANCE
BEHAVIOR OF ANCHORAGE TYPE OF STRUCTURE

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2008, 27 (S2): 3553-3553 doi:

[PDF] 311 KB (1241)

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Based on the analysis of a large number of relevant literatures at home and abroad，the research progress of the explosion-resistance behavior of anchorage type of structure is reviewed，and the common problems are pointed out：(1) the deficiency of the research on the explosion-resistance behavior of composite anchorage type of structure；(2) the need of further research on the application of special composite anchorage structure；(3) the reinforcement of the research on new anchorage type of structure；and (4) the improvement of experimental research and application results to systematical，strict and acknowledged theoretical explanations.

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3D GEOLOGICAL MODELING METHOD BASED ON GIS AND VIRTUAL REALITY MODELING

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2008, 27 (S2): 3563-3563 doi:

[PDF] 225 KB (1648)

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A new method for 3D geological modeling is introduced，which is based on the GIS and the virtual reality modeling language(VRML). Through getting the stratum information of each borehole，which stores in GIS，the system automatically analyzes this information and draws the profiles chart of the side faces of the model，and at the same time，the system writes VRML script file to build 3D geological model. According to the above concept，a system is developed and successfully applied to create 3D geological model of a bridge pier site. The model can be shown in internet by web browser and can be free rotated，zoomed in or zoomed out. The main advantages of this method are fast and real time in geological modeling，which can be used as an aid decision system to check the stratum information.

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INFLUENCE OF INCLINATION ANGLE AND AZIMUTH ANGLE OF BOREHOLE ON CREEP OF SALT ROCK

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2008, 27 (S2): 3570-3570 doi:

[PDF] 248 KB (1249)

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Salt rock can make borehole close in the effect of creep，which often leads to stuck. However，many analytical models for creep of salt rock are based on the two-dimensional models currently，which are hard to analyze the problems of stuck because of creep in controlled directional well. Based on space coordinate transformation，the 3D model of creep of controlled directional well is established，and the variations of stresses with the actual deviation and azimuth angle are transformed to the hole axis. The established model analyses the influence of the variation of deviation and azimuth angle on creep under certain stress，and also propounds the concept that the “sensitive zone”of creep exists in parameters of some borehole of the directional well，which offers references to optimize the design of some parameters to drill out the salt formation successfully. Through actual example，it is verified that the security mud density based on the 3D numeral model is suitable during drilling the salt layer，which gives instruction of security mud density in practicing directional drilling in salt formation.

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EXPERIMENTAL INVESTIGATION ON STRENGTH AND DEFORMATION OF PLAIN HIGH-STRENGTH HIGH-PERFORMANCE CONCRETE UNDER MULTIAXIAL COMPRESSION

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2008, 27 (S2): 3575-3575 doi:

[PDF] 393 KB (1340)

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The strength and deformation experiments of plain and high-strength high-performance concrete (HSHPC) and normal strength concrete(NSC) with various stress ratios under uniaxial，biaxial and triaxial compressions are completed，using the large static-dynamic true-triaxial machine. The multiaxial compression tests are performed on 100 mm×100 mm×100 mm concrete specimens with friction-reducing pads(three layers of butter and three layers of plastic membrane) placed between platens and specimens under monotone proportional loading. Failure modes and failure mechanism of specimens are described. The multiaxial strengths，strains under peak stress and stress-strain curves are measured；and the influence law of the stress ratios and the difference of multiaxial mechanical property between HSHPC and NSC are also analyzed. The experimental results show that ultimate strength s3f and principal strain e3p of HSHPC and NSC under multiaxial compression are greater than uniaxial compressive strength ¦c and strain ecp under all stress ratios respectively，especially under triaxial compression. Moreover，the increasing multiple ratios of s3f and e3p relatively to ¦c and ecp depend on brittleness-stiffness of concrete，stress state and stress ratios. The formula of Kupfer-Gerstle and Ottosen¢s failure criterion for plain HSHPC and NSC under biaxial compression and multiaxial stress states is proposed，which provide experimental and theoretical foundation for strength analysis of HSHPC and NSC structures such as bridge and tunnel engineering，underground engineering，and building engineering，etc..

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RESEARCH ON INVERSION OF JOINT¢S ATTITUDE USING REFLECTED STRESS WAVE

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2008, 27 (S2): 3585-3585 doi:

[PDF] 320 KB (998)

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The joint is crucial for rock mass engineering，so the inversion of the joint¢s attitude using stress wave is of great engineering significance. Based on the theory of analytic geometry，a formula to calculate traveling time of the reflected wave can be deduced from which direct relationship between a joint¢s true dip direction，true dip angle and the traveling time of measure points can be established. Through complex signal analysis，instantaneous amplitude，phase and frequency of signal can be presented. The signal obtained by the test of jointed rock mass simulation shows that despite the serious interference of Rayleigh wave，the initial arriving moment of the joint reflected wave can still be estimated by instantaneous frequency efficiently. Using the complex signal analysis，the traveling time of several measure points distributing around the source of vibration is gained. And a program based on MATLAB is written to search the center of the isochronous circle，therefore，the inversion of joint¢s attitude can be achieved in the end.

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FINITE ELEMENTS METHOD STUDY ON DYNAMIC ROCK BREAKING IN AIR DRILLING

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2008, 27 (S2): 3592-3592 doi:

[PDF] 871 KB (1435)

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Air drilling is a kind of under-balanced drilling technology with air，whose rock breaking form is different from conventional mud drilling. Based on rock mechanics and elastoplastic mechanics，a 3D non-linear dynamic model of dynamic rock breaking with full gauge PDC bit is established using finite element method (FEM)，in which anisotropy，strata dip and friction factor of drilling bit and rock are considered. The mechanism and process of dynamic rock breaking in air drilling are studied. And the stress and strain of borehole、shaft wall and bottom hole after rock breaking are analyzed as well. It shows that the rate of rock breaking in air drilling is faster in bottom hole where the tensile stress is larger，and the shaft wall is quiet stable under dry air；however，it would collapse in blocks in case of instability. And the change law of hole deviation and azimuth in anisotropic formation in air drilling is obtained by investigating the displacement of drilling bit with time variation. The model provides a new method for the study of breaking mechanism，the change of deviation and stability of shaft wall，and it offers theoretical basis for the development and optimization of bit and drilling tool in air drilling.

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A NEW METHOD FOR PREDICTING VISCO ELASTIC DEFORMATION IN ROCK ENGINEERING

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2008, 27 (S2): 3598-3598 doi:

[PDF] 205 KB (857)

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Aimed at viscoelastic deformation prediction in rock engineering，an incremental formula of relative displacement is deduced based on Goursat expression of elastic displacement and elasticity-viscoelasticity analogy principle，and a deformation predicting model with methods and steps is proposed. It does not need the true values of time，boundary condition and physical property parameters of the rock mass，but obtains a group of combination values. The proposed method considering constitutive character of the rock mass can predict two-dimensional long-term deformation without stress and displacement boundary conditions. Then，it is applied to slope engineering，in which the comparison between predicted and measured deformation indicates that the method has high short-term prediction precision with error smaller than 10%，while the error is about 23% in the long-term prediction. At last，the engineering applicability of the method is discussed by an example of slope excavation which provides theoretical foundation and practical method for predicting two-dimensional long-term visco-elastic deformation of rock engineering.

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NUMERICAL SIMULATIONS OF WATER INRUSH OF FAULT F0 IN FANGEZHUANG COAL MINE

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2008, 27 (S2): 3604-3604 doi:

[PDF] 347 KB (987)

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The fault F0 of the Fangezhuang coal mine，Kailuan coal group，runs through the whole mine field. Based on the experimental results of the creep for the faults，the data of the faults under different conditions obtained. The influence of mining activity on the faults at different periods is gained through the simulation of fluid-solid coupling and the calculation of seepage creep using numerical simulations software FLAC3D. The results indicate that vertical displacement of floor strata near the faults reaches maximum value. Large tectonic stress on the floor is caused by the faults，which leads to a wide range shear stress area at the same time. The stress concentration is the key factor of the breakage and water bursting of floor. The basic phenomena including the influence of confined water on the overlaying rock and faults，the influence of mining activity on the floor strata，the size and range of influence of the mining activity on the faults，and the time-effect of the influence on the confined water，are described by the simulation results very well，which provides reliable basic data for the safety of the coal production.

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STUDY ON MOVEMENT AND DEFORMATION OF GROUND AND SOIL AND ROCK MASS RESULTED FROM EXCAVATION OF TUNNEL WITH CIRCLE SECTION

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2008, 27 (S2): 3611-3611 doi:

[PDF] 270 KB (1096)

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Tunnel excavation will affect the safety of the surroundings，which induces the displacement and deformation of the above ground. Based on the stochastic medium theory，formulas for predicting the displacement and deformation of the ground and rock mass induced by tunnel excavation are deduced，especially for the tunnels with circle section. Because of the difficulty in the integration，semi-analytical solution of prediction of the displacement and deformation of the above ground is obtained through integrating the horizontal direction and dividing many strips along the depth. Furthermore，a program is developed to compute the movement and deformation of the ground and rock mass resulted from excavation of the tunnel with circle section，which is convenient to be applied in the engineering. Finally，according to the classification of the construction protection，the safety estimation of the influence on the surroundings induced by tunnel excavation is discussed and the criterion of ground deformation failure is put forward，namely，it is in danger when the ground horizontal deformation is larger than 6 mm/m，otherwise，it is safe. Through an engineering example，the theoretical results and the on-the-spot survey data are consistent，which proves that the computing methods provided are reasonable. The results of the research are significant for tunnel safety construction，and it would be beneficial for the reduction of damage in the constructions and establishments induced by the tunnel excavation.

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REVIEW OF INTERACTION MECHANISM BETWEEN SURROUNDING ROCK AND SUPPORT AND ANALYSIS OF CONCEPTUAL MODEL OF RHEOLOGICAL DEFORMATION MECHANISM

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2008, 27 (S2): 3618-3618 doi:

[PDF] 265 KB (1559)

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The essence of underground rock engineering supporting theory is interaction mechanism between surrounding rock and support. A detailed analysis of defects and errors in Kastner equation and current interaction mechanism is given as follows：(1) mechanical treatment of support reaction in the Kastner model may be flawed in its supporting time and loading path，which can not be used in engineering practice；(2) the ground characteristic curve deduced from Kastner equation doesn¢t exist practically and can not intersect with support reaction line；and (3) the equilibrium point solved by the intersection of ground reaction curve and supporting characteristic curve is wrong conceptionally and logically. Then，the conceptual model of rheological deformation mechanism is established. The calculations of project examples are offered，in which the course of the interaction between surrounding rocks and support is derived. It is proven that the concrete structure can be applied to the supporting structure of the tunnel in soft rock theoretically. The conceptional model of the rheological mechanism referred gives the qualitative explanation for the interaction between surrounding rock and support，and can be applied to the design and calculation in underground rock projects. The theoretical basis of the mechanism model is reliable，and has a bright future in engineering practice.

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STUDY ON PREDICTION METHOD OF FRACTURE TOUGHNESS OF ROCK MODE II BY LOGGING DATA

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2008, 27 (S2): 3630-3630 doi:

[PDF] 257 KB (1255)

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According to the theory of computing stress intensity factor by straight-notched Brazilian disc(SNBD) specimens，a set of experimental equipment is designed and constructed to test fracture toughness of rock mode-II. 20 rock specimens are prepared from pay zone and barrier layer between 1 500 and 2 000 m in WG oil field，China，and the tests are conducted successfully. Based on the experimental results，the relationship among fracture toughness of mode II，confining pressure and tensile strength is analyzed with the least square method，and the prediction model of fracture toughness of mode II is established by the geophysical logging data. Finally，the fracture toughness mode II is predicted，which is verified in field application by combining the KIIc prediction mode with the horizontal in-situ stress and tensile strength prediction based on acoustic logging，density logging and GR logging data from Well H341. The method is beneficial for solving the lack of continuous fracture toughness mode II along the well bore in field hydraulic fracturing operation.

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RESEARCH ON EFFECT OF LOADING CONDITIONS ON FAILURE PROCESSES OF ROCKS WITH DIFFERENT SIZES UNDER UNIAXIAL COMPRESSION

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2008, 27 (S2): 3636-3636 doi:

[PDF] 302 KB (1677)

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Based on the phenomenon of loading condition sensitivity，which exists in the uniaxial compression tests of rocks，a numerical study is conducted to investigate the effect of loading conditions on the deformation behaviors and failure patterns of rocks with different sizes and shapes under uniaxial compression，using a self-developed numerical code EPCA2D. It is concluded that，for rocks with the same homogeneity，the size and shape effects are mainly caused by the mismatch of mechanical properties between rock specimen and loading platen. The simulation results agree with the experimental phenomenon well. Different friction conditions between loading platen and specimen¢s ends are considered in the simulation. Results indicate that the discreteness of uniaxial strength and deformation behaviours with different frictions exist even when the frictions are reduced to a very low value. Therefore，it is unfavourable to improve the experimental quality by reducing the frictions.

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RESEARCH ON REPRESENTATIVE ELEMENTAL VOLUME (REV) OF DEFORMATION CHARACTER OF JOINTED ROCK MASS BASED ON NUMERICAL EXPERIMENT

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2008, 27 (S2): 3643-3643 doi:

[PDF] 205 KB (1152)

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According to random joint program，several groups of numerical models on random joint rock mass are obtained. The stress-strain curves of these models are gained by numerical test. Firstly，the changing law of the deformation curve on these numerical samples under certain confining pressure is considered under the same probabilistic distribution parameters of random joint and the same sample size conditions. Then，the effect on the stress-strain curve caused by sample size is considered. Through the above two kinds of computing schemes，it is found that the deformation curves become dispersal when the sample is small，and become uniform with the enhancement of size. It illustrates that the size effect exists among these curves，and the size of rock mass deformation feature can be obtained by numerical test.

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FRACTAL ANALYSIS OF ENERGY CONSUMPTION OF ROCK FRAGMENTATION IN ROTARY DRILLING

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2008, 27 (S2): 3649-3649 doi:

[PDF] 221 KB (1117)

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According to the fractal theory，a fractal model for consuming energy on rock fragmentation is provided through energy consumption analysis of rock fragmentation in rotary drilling. The factors，such as size distribution of rock cuttings and energy consumption in the process of drilling are taken into account and the factors affecting energy consumption of rock fragmentation on the bit are considered. The model shows that the energy consumption on rock fragmentation is not only related to the drilling parameters such as weight on bit and rotational speed，but also the size of rock cuttings and the fractal dimension of size distribution. The model can be used to determine the necessary energy consumed on rock fragmentation and it can also be inversely used to optimize drilling parameters with the energy consumption on the rock fragmentation. In addition，the three classical formulas of the crushing work ratio theory can be obtained by properly simplifying the model，hence，the general applycation of the model is proved.

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APPLICATION OF 3D VISUALIZATION MODELING
TECHNOLOGY TO ROCK MASS QUALITY EVALUATION

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2008, 27 (S2): 3655-3655 doi:

[PDF] 947 KB (1317)

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The structural characteristic of rock mass plays an important role in rock mass engineering construction，so correct evaluation of rock mass quality is of great engineering significance. Based on the collection and analysis of massive data，taking advantage of 3D visualization engineering software，3D engineering rock mass and block models are reconstructed by means of a new data structure and method. Then，effective estimation of 3D geological block models is made by geological statistics. Finally，block models with different indexes are combined using set operation algorithms of space pattern so as to analyze and evaluate rock mass quality. The theory is applied to rock mass quality evaluation in the third mining zone of Jinchuan mine with satisfying application efforts.

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APPLICATION OF EVALUATION OF REINFORCEMENT DEMAND DEGREE TO REINFORCEMENT OF LEFT BANK OF LONGTAN HYDROPOWER STATION

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2008, 27 (S2): 3661-3661 doi:

[PDF] 201 KB (861)

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Evaluation of the effects of slope reinforcement is one of the key factors in slope reinforcement. Evaluation methods can be broadly classified into two categories. The first category is the analysis of engineering geological conditions and qualitative research or semi-stable method on rock mechanical，which is short of accuracy. The second category is the quantitative evaluation method based on the analysis of field monitoring，which is insufficient because the judgment based on the monitoring data cannot be obtained unless the measuring point is installed and monitored. Degree of reinforce demand(DRD) is a new evaluation method with unique advantage，which combines the two methods mentioned above in order to make best use of their advantages and bypass the disadvantages. The 435 m-high excavated slope of Longtan Hydropower Station in Guangxi threatens the security of the dam，whose deformation and stability are of great importance to the power station. To demonstrate the DRD evaluation，an application in zone A on the left bank of the hydropower station is described. The evaluation results indicate that the reinforcement of the slope is fairly effective，which agrees well with the monitoring data and the field investigation results.

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STUDY ON MONITORING OF DEFORMATION AND STREE STATE
OF LANDSLIDE ANTI-SLIDE PILES USING
BOREHOLE INCLINOMETER

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2008, 27 (S2): 3667-3667 doi:

[PDF] 666 KB (1390)

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The horizontal lateral displacement of reinforced concrete or rail anti-slide piles is measured by setting up borehole incline-tube in pile. For reinforced concrete anti-slide piles，it is considered as beams on elastic foundation so as to obtain elastic curve differential equation，and the rotating-angle，bending moment，shear and resistance of soil or rock piles are deduced then. For rail anti-slide piles，the bending moment，normal stress and anti-slide force of rail anti-slide pile are calculated inversely based on flexure deformation measured by inclinometer. Finally，this method is applied to Hanjiaya and 0509 landslide with satisfying effects.

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DEFORMATION STATISTICAL REGRESSION ANALYSIS MODEL OF SLOPE AND ITS APPLICATION

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2008, 27 (S2): 3673-3673 doi:

[PDF] 499 KB (1418)

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Taking into account the influential factors including time，temperature and rainfall，a deformation statistical regression analysis model for slope is established. The visualization for deformation regression and forecast is realized through Microsoft Visual C++ and stepwise regression algorithm in self-developed monitoring information management and monitoring data analysis network system of geotechnical slope engineering. The system has been used to conduct statistical regression analysis of monitoring data of a large-scale high slope of Longtan Hydropower Station，and the results indicate that the statistical regression data for deformation are accordant with measured data，in which the statistical multiple correlation coefficients between them are large and the surplus standard deviation is small. The statistical regression analysis model efficiently reflects the changing law and developing trend of deformation of slope. The model and system provide efficient analysis means for evaluating safety properties and forecasting deformation development trend of slope.

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FIELD TEST ON COUNTERFORCES AGAINST TENDON BEAM OF PRESTRESSED CABLE FRAME OF SOIL-LIKE SLOPES

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2008, 27 (S2): 3680-3680 doi:

[PDF] 237 KB (1121)

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The counterforces applied under beams are tested on the site，which is carried out on a granite eluvium slope reinforced with prestressed cable beams along the expressway from Shantou to Jieyang. The data of the counterforces are obtained from the earth-pressure cells under the bottom of beams. It is put forward that under a definite prestressed force，the distribution discipline of the counterforce along the length of beam is quadratic parabola rather than linear or uniform one. The axial force of the main reinforcement in the beams is also tested at the same time，which leads to the conclusion that the distribution discipline along the length of a beam is also quadratic parabola. The distribution discipline obtained from the test confirms that the distortions of the beams are objective. Considering the distortions of the beams，the bending moment along the vertical beam is calculated based on differential equation of beams. The results indicate that the distribution discipline of bending moment along the length of beam is cubical parabola. Both the cubical parabola distribution of the bending moment and the quadratic parabola distribution of the counterforce are accord with the stress-strain and deformation of the beams.

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ANALYTICAL METHOD OF SEARCHING NONCIRCULAR SLIP SURFACE BASED ON SIMULATED ANNEALING OPTIMIZATION ALGORITHM

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2008, 27 (S2): 3686-3686 doi:

[PDF] 220 KB (1077)

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Based on the real stress field in soil slope obtained by nonlinear finite element method，the finite element technique for stability analysis of slopes is integrated with the simulated annealing method，which is artificial intelligence method. The searching technique of the minimum safety factor and the non-circular critical slip surface of slope is discussed. To resolve the limitation that the initial or trial slips can not accord with the constraint conditions in configuration during the process of searching critical slip surface，the conception of dynamic search domains is utilized which has the advantages of localized transform process and high efficiency. The test results demonstrate that this algorithm can pick out the global critical slip surface，and the circular or non-circular critical slip surface is reproduced as well.

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NUMERICAL ANALYSIS AND COMPREHENSIVE COMPARISON
OF STABILITY AND REINFORCEMENT OF ROCK SLOPE

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2008, 27 (S2): 3692-3692 doi:

[PDF] 268 KB (1256)

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Because of the existence of discontinuities such as faults and joints，rock masses have dual characteristics- continuity and discontinuity. Since there is no applicable method to treat the duality at present，it is encouraged to conduct comprehensive comparison using different numerical analysis methods. The analysis of stability and reinforcement of the rock slope in Pubugou Hydraulic Project is taken as an example to show the methodology of the comprehensive comparison study，in which finite element method(belongs to equivalent continuous medium approach) and block element method(belongs to discontinuous medium approach) are applied. Through the comprehensive comparison of the calculation results，the stability and reinforcement schemes of the slope are calibrated. The study also shows that：(1) if the influences of the persistence ratio of joints are considered in the strength parameters only，finite element method and block element method present close results with minor differences；(2) compared with block element method，finite element method provides larger displacement，yield zone and the rock bolt stress. The reason is that the deformation of the intact rock can be considered in the finite element method，while the block element method can only take the deformation of joints into consideration.

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STABILITY STUDY ON RESERVOIR ACCUMULATION BODY CONSIDERING PHYSICAL AND CHEMICAL REACTIONS BETWEEN WATER AND ACCUMULATION BODY —TAKING XIAZANRI ACCUMULATION BODY FOR EXAMPLE

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2008, 27 (S2): 3699-3699 doi:

[PDF] 248 KB (1308)

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Taking Xiazanri accumulation body for example，the parameters of accumulation body under natural situation and after physical and chemical reactions with reservoir water are obtained using large-scale horizontal push-shear in-situ test. Based on these parameters，numerical model to calculate the safety factor of reservoir accumulation slope is built. The results show that under two situations(with/without considering chemical and physical reactions between water and accumulation body)，the changing trend of safety factor of slope is the same as the reservoir water level ascends，which decreases at first and then increases. However，compared with the former，the factor of safety under the latter situation decreases more，and decreasing ratio can reach 35.34% or more. Therefore，factor of safety calculated only considering the water-rock mechanical reaction is not reliable in practical engineering design.

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THEORETICAL ANALYSIS AND MODEL TEST STUDY ON DEFORMATION MECHANISM OF CREEP LANDSLIDE

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2008, 27 (S2): 3705-3705 doi:

[PDF] 268 KB (1197)

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In allusion to a certain landslide of Xiangfan—Shiyan Expressway，some works have been done to find out its geological genesis，material composition，mechanical properties，structure features and motion characteristics based on which the deformation mechanism is analyzed. In addition，large-size geomechanics modelling test is adopted in order to study the process of development，evolvement，form in long geological history period in laboratory，and the curve of the displacement of the rheological model is compared with the data of laboratory physical model test and the monitoring. It is concluded that the creep-sliding characteristics are well reflected by the rheological mode.

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STUDY ON BENDING CREEP MECHANISM AND TIME-DEPENDENT DEFORMATION CHARACTERISTICS OF LANDSLIDE WITH DOUBLE SLIDING PLANES AND ROCK-LAYER REVERSE

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2008, 27 (S2): 3712-3712 doi:

[PDF] 750 KB (927)

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To study the deformation and destruction mechanism of landslide with double sliding planes and rock- layer reverse，using Hanjiaya landslide in Xiangfan—Shiyan expressway as example，bending creep condition and mechanism of reverse rock-layer are expounded deeply；the time-dependent deformation equations concerning the bending creep characteristics of rock layer are established by combining with nonlinear creep model and creep buckling equation of reverse rock layers under the condition of plane strain. It brings forward a clue to forecast the stability of the landslide according to the deformation rate of bending creep of reverse rock-layers and discusses creep buckling instability mechanism characteristic under different load levels. The qualitative comparison between in-situ monitoring and analytical results indicates that in the rain season，when the loading level of landslide foreside ＞＞，the gradual accumulation of rock-layer reverse deformation，and deferred instability failure of the landslide occur；in the dry season，when the loading level is ，the landslide is in temporary stable condition. In conclusion，it is reasonable and feasible to analyze and evaluate the landslide with the model proposed.

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ANALYSIS OF STABILITY ZONING OF HIGH SLOPES USING MAXIMAL LYAPUNOV EXPONENT BASED ON MULTIVARIATE TIME SERIES

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2008, 27 (S2): 3719-3719 doi:

[PDF] 216 KB (1071)

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The maximal Lyapunov exponent(MLE) can reveal the nonlinear chaos feature of the dynamical evolution of steep slopes，and the MLE derived from multivariate time series is more practical than univariate time series. The 3D multivariate phase space reconstruction is investigated. Then，the modified method of bi-direction search is developed for calculating the MLE from 3D deformation time series based on the reversible and irreversible properties of time trajectories. Finally，the proposed method is applied to the high slope No.2 at Xiaowan Hydropower Station. Bottom-up towing deformation mechanic of this slope is obtained by the MLE used as the judging criterion of slope stability zoning，which agree well with practical situation. Thus，the proposed method is proven to be effective and reliable，and the research results have useful references to the evaluation and prevention of stability zoning of high slopes.

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STUDY ON DISTRIBUTED OPTICAL FIBER SENSOR-BASED MONITORING FOR SLOPE ENGINEERING

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2008, 27 (S2): 3725-3725 doi:

[PDF] 353 KB (1721)

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Real-time and on-line monitoring of slope and reinforcement works are useful for mastering the deformation dynamics and early warning of the landslide in time. In comparison with the conventional monitoring methods，distributed fiber optic sensing offers a number of advantages including distributed monitoring，long distance，real-time monitoring，long-term stability，et al. so as to meet the demand of early warning of landslide and health monitoring of slope engineering. The measurement principles and merits of Brillouin optical time-domain reflectometer(BOTDR) are introduced. And a novel distributed fiber optic sensor-based monitoring system for slope engineering is expounded. The relative topics about application of BOTDR in slope engineering are discussed including installation methods of optical fiber，optical fiber protection and temperature compensation method. To realize the remote distributed monitoring of the slope and reinforcement works，fiber optic sensors，which are connected with each other to form a BOTDR-based remote distributed monitoring system，are installed in the reinforcement works and the slope in some ways. Then taking a project as example，the deformation monitoring data are analyzed. And the monitoring results show that，in slope engineering，the state of deformation can be exactly reflected by BOTDR-based distributed monitoring system，which has obvious advantages in terms of slope deformation monitoring and real-time landslide prediction.

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EXPERIMENTAL RESEARCH ON RHEOLOGICAL CHARACTERISTICS OF WEAK STRUCTURAL PLANES OF HIGH SLOPES IN COAL STRATA IN A HYDROPOWER STATION

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2008, 27 (S2): 3732-3732 doi:

[PDF] 330 KB (1104)

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In view of developmental features of the weak structural planes of excavation high slopes in the coal strata，the shearing rheological test device for the weak structural planes is designed and built in the saturated situation. The time-dependent deformation characteristics of the weak structural planes in the coal strata are studied systematically. On the basis of rheological mechanical tests，which lasts for nearly 1 year，the comprehensive time-dependent constitutive equations of each type of the weak structural planes are established，and the long-time strength parameters are acquired by adopting Burgers rheological constitutive equation. The results of rheological tests show that the long-term cohesive force of the weak structural planes c ranges from 57 to 160 kPa under the saturated conditions，and j is between 12° and 18°，which decreases about 60% in contrast with that of saturated quick portable shearing test. The results obtained are important for feedback analysis，deformation mechanism and optimum design of slope related to safety of stabilization during the reservoir operation in engineering region. And referenced constitutive model is provided for the similar weak structural planes of high slopes.

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ASSESSMENT ON FAULTS SLIDE CRITERION AND STABILITY AND BACK-ANALYSIS OF TECTONIC STRESS FIELD

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2008, 27 (S2): 3740-3740 doi:

[PDF] 241 KB (1316)

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For the study of the relationship between the dynamic phenomena in mines such as mine earthquakes，outburst and faults slide，extraction depth，firstly，double shear friction experiments of sandstone have been carried out so as to achieve its slide criterion in engineering aspects. Secondly，in order to study the stability of underground rock and zone of tectonic stress field，based on the analysis of distribution characteristics of initial rock stress measurements，the geology structural model is built according to the feature of underground rock，and tectonic stress field is obtained by back-analysis using finite element method. The calculating results agree well with the analysis result of earthquakes mechanism and the distribution characteristics of the measurements. The high stress regional centers locating at discontinuous zone of I level faults are corresponding to underground earthquakes scene. The study shows that existence of tectonic stress is the major origin and necessary condition of mine earthquakes. The instability sliding of the faults is the main manifest and the mining activity is the leading factor. Beipiao fault has dominated effects on other sub faults and tectonic stress areas and is dynamical fountain of dynamic phenomena in the Beipiao Mines.

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NUMERICAL SIMULATION AND MONITORING ANALYSIS OF
BEDDING LANDSLIDE

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2008, 27 (S2): 3746-3746 doi:

[PDF] 309 KB (1227)

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A typical example argillite bedding landslide at the K31+160–K31++460 of Changzhi to Jincheng highway is presented. By using numerical simulation software Geoslope，the states of slope under the full face excavation without engineering protection on the original design and the effectiveness of reinforced slope after design changed are simulated. The updating status of reinforced slopes after design changed is being monitored and analyzed. It provides the scientific basis for dynamic designing，information construction of landslide combing numerical simulation with monitoring analysis based on comprehensive updating recuperation. Finally the successful control practical experiences show：(1) controlling landslide does not only consider resistive engineering，but also enhance discharge underground water that influence the weak interlayer of landslide；(2) the method by controlling the landslide that combing the numerical simulation reflecting the integrality stress and strain with the monitoring information of several key points of the whole slope can propose a new method for complex landslides reasonable design and successful control.

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STUDY ON GENETIC MECHANISM OF TRANSLATIONAL LANDSLIDE

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2008, 27 (S2): 3753-3753 doi:

[PDF] 1448 KB (1620)

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According to the physico-mechanical parameters of the Tiantai Village landslide，the physical simulation was preformed. The deformation and failure evolution of the translational landslide，which is caused by the cooperation of the hydrostatic pressure and the uplift pressure，are reconstructed. The clear relationship between the critical water head and the dip angle of the sliding plane is revealed by the results：the larger the dip angle of the slide plane is，the smaller the critical head would be under the same physico-mechanical parameters of rock and soil in the landslide，and vice versa.

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NUMERICAL SIMULATIONS OF LAYOUT OPTIMIZATION AND CONSTRUCTION PROCESS OF UNDERGROUND POWERHOUSE WITH EXPLICIT FINITE DIFFERENCE METHOD

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2008, 27 (S2): 3760-3760 doi:

[PDF] 600 KB (1247)

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Numerical simulation is one of the main approaches to deal with such problems as reasonable layout and construction of underground powerhouse. The computer codes for fast Lagrangian analysis of continua，FLAC and FLAC3D，with the explicit finite difference method are regarded to be suitable respectively for both two- and three-dimensional numerical simulations of problems involving supported construction process in geotechnical engineering. As an engineering example，the cavern group of the underground powerhouse of Guandi Hydropower Station on the Yalong River in Southwest China is analyzed. The two-dimensional FLAC analysis is performed firstly for the optimization of location and spacing schemes of the three main chambers，i.e. the generator chamber，the main transformer chamber and the tail water surge chamber，considering their parallel arrangement and the modeling efficiency and computing cost. Then，the entirely-supported construction process of the cavern group of the underground powerhouse under the determined optimal layout scheme is simulated in three dimensions with FLAC3D. The distributions of displacement，stress and plastic deformation in the rock masses surrounding the caverns and the loads carried by the supporting structures are obtained. It is proven by the results that the numerical simulations of the layout and construction process of underground powerhouse with explicit finite difference method using respectively FLAC2D and FLAC3D match those of the practical case. The results from nonlinear stress analyses can be used to guide the design of excavations and rock supporting mechanisms.

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STABILITY STUDY OF LARGE UNDERGROUND CAVERNS
UNDER HIGH GEOSTRESS

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2008, 27 (S2): 3768-3768 doi:

[PDF] 626 KB (1548)

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The Laxiwa Hydropower Station，constructed in high mountain with steep slope and deep gorge，is the largest hydropower station in Yellow River area. Its underground powerhouse consists mainly of main powerhouse，auxiliary powerhouse，main transformation cavern，pressure adjustment well，caudal shiplock cavern，and caudal water tunnel，which has vertical depth of 282–429 m. The granite is weakly weathered in the area of the underground powerhouse，with grey-grey white，middle coarse size，block structure and mineral component of mainly feldspar. The underground powerhouse cavern group is in high stress field with the maximal principal stress of －22–－29 MPa. In order to evaluate the stability of hard rock cavern group under high geostress，a new method，named PFP(preparation，feedback and prediction)，is presented. It is carried out by three phases along with the progress of the excavation of the underground caverns in Laxiwa Hydropower Station. The results show that the deformations of rock wall are different in different spaces and increase with the step of excavation；the sequential tunnelling layer makes the stress undulation and transfer；the stress looseness zone is greatly different from the normal tunnel because of cross-caverns；the EDZ has different failure models and depths in different positions，and so on. The study proposes scientific suggestion for excavation and supporting of the caverns，which is also identified by the mechanical behaviour of rock in practice. The method and conclusions can offer a useful reference for other similar underground projects.

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THREE-DIMENSIONAL GEOSTRESS MEASUREMENT
AND GEOMECHANICAL ANALYSIS

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2008, 27 (S2): 3778-3778 doi:

[PDF] 269 KB (1415)

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For there is dissension in the maximum principal stress orientation obtained by in-situ measurements by different means，geostresses in the three directions are presented by in-situ measurement and geomechanical analysis，to investigate the status of stability of rock mass of bilateral dam abutment and get reliable theoretical foundation for its design and construction. The in-situ measurement adopts stress relief by overcoring method，using bore strain gauge 36–2 to collect data. And the elastic modulus experiment is conducted indoors. In terms of these experimental data，the magnitude，azimuth，inclination of the geostress of rock mass of dam abutment can be figured out，through which the distribution character of the ground stress of rock mass of the hydraulic engineering can be determined. By geomechanical method，the in-situ geological information about conjugate joints，fault occurrence，rake angle，shift symbol of fault slip and so on are analyzed，through which the principal stress orientation can be elicited by stereographic projection. By the study of the above two aspects，some conclusions are drawn：(1) The in-situ metrical results accord with the geomechanical results well，which indicates better reliability. (2) The mode of stress action in the region of measurement point gives priority to terrain and tectonic stress control. The magnitude of the maximum principal stress is between 11.8 and 20.8 MPa，and the direction as a whole is NW-NNW in the left bank，and N-NNE in the right bank，parallel to the bilateral cliff faces approximately and inclining to the bottom of the cliff. (3) Three-dimensional stress state in the region belongs to the potential strike-shift pattern.

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STUDY ON RECENT STATE OF STRESS IN DEPTH 1 000 M OF
JINCHUAN MINE

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2008, 27 (S2): 3785-3785 doi:

[PDF] 244 KB (1107)

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The Jinchuan mine is a large copper and nickel deposit，and the mine district No.2 is one of the key deposits of the Jinchuan nickel mine. At present，this district goes into the deep mining. The drifts are strongly deformed and severely damaged by deep mining. In order to study stress state in deep mining，geostress survey is carried out in mine district No.2. In-situ stress measurement is carried out by hollow inclusion gauge method，and three-dimensional stresses at seven measuring points are obtained. The measurement results show that at the depth 700 to 800 m from underground，the maximum principal stress is about 20 to 30 MPa. For most of the measuring points，the maximum principal stresses are in the direction of NNE-NE，and the dip angle of them is above 40°；and the stress state governed by the horizontal stress changed obviously.

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CORROSION INVESTIGATION AND MECHANICAL BEHAVIOR TEST ON SUPPORT OF BOLTS IN underground drift

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2008, 27 (S2): 3791-3791 doi:

[PDF] 259 KB (1682)

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The corrosion environment of an underground drift of one coal mine and the corrosion status of in-situ split-set bolts，which are embedded in the drift for 10 years，have been investigated. The content of the corrosive mass in the underground water，the general mass loss and the local pit corrosion situation of the bolts are tested. The tensile test is carried out to analyze the peak bearing capacity and the plastic behavior. The obtained results are as follows：the corrosion of the split-set bolts without any protection is very serious，and most of the investigated specimens are nearly out of service. The outer corrosion of the bolts is mainly pit corrosion，and the inner corrosion is nearly uniform corrosion. The pit corrosion amount，area，and depth，etc. all follow certain scatter law；moreover，there is an inherent connection between the pitting area and the pitting depth. The pitting corrosion and punches on the bolt surface have great impairment on the mechanical behaviors of bolts. The loss ratio of the elongation percentage of the bolts is much greater than that of the peak bearing capacity，which shows that the impairment of the corrosion on the plasticity of the bolts is more server than that on the bearing capacity of the bolts. Therefore，the deformation of the bolt before its failure is difficulty to be monitored，and emergent hazards will easily happen.

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NUMERICAL ANALYSIS OF DYNAMIC RESPONSE OF SATURATED POROUS SEABED-PIPELINE UNDER SEISMIC LOADING

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2008, 27 (S2): 3798-3798 doi:

[PDF] 351 KB (1394)

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Seismic-induced pore water pressure and effective stresses in the saturated porous seabed under seismic loading are the main factors that govern the overall stability of submarine pipelines. In most of the previous investigations of dynamic response of seabed，the pipeline is taken as to be rigid and generally the interaction between seabed and pipeline is overlooked. The equivalent disposal of seabed boundary also has not been taken into consideration. Therefore，the model of the seabed-pipeline interaction is established based on the Biot¢s theory of consolidation. The distribution of the seismic-induced pore water pressure along the pipeline outer surface and the dynamic response of submarine pipeline along the pipeline inner and outer surface under El Centro seismic wave are studied with ADINA. The effects of variable pipeline radius and pipeline wall thickness，variable soil modulus and soil permeability on the seismic-induced pore water pressure and internal stresses of submarine pipeline are discussed. Through numerical analysis，viscoelastic artificial boundary is taken into account to simulate the transmission of seismic wave from finite region to infinite region effectively. It actually shows the validity and accuracy of dynamic response of submarine pipeline under seismic loading.

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STUDY ON CHAOS DYNAMIC FEATURE OF SURROUNDING ROCK DISPLACEMENT OF UNDERGROUND POWERHOUSE

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2008, 27 (S2): 3807-3807 doi:

[PDF] 412 KB (1196)

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Taking the multi-point displacement data of the main powerhouse surrounding rock as example，through multi-point measuring displacement data from different sections of surrounding rocks in underground powerhouse of Xiaowan Hydropower Station，the chaos dynamic features of displacement data of underground powerhouse are studied by applying the power spectrum analysis method，and G-P method is improved to gain correlation dimension D；then the maximum Lyapunov exponent( ) is calculated by reconstruction phase space with adaptable parameters m，t that are obtained through synthetic analyzing G-P method，C-C method and multiple autocorrelation method. Results show that all the measuring multi-point displacement data in roof and of depth 30 m in abutment don¢t have chaos dynamic feature，but data from depth 2，7，15 m in abutment，the wall and those pre-measuring multi-point displacement data gained from constructing branch and drainage caves have chaos dynamic feature. The power spectrum graph has been gained to reflect chaos dynamic feature of displacement data. Correlation dimension D and the maximum Lyapunov exponents are greater than zero. For the displacement data，which have chaos characteristics，many methods can be used during excavation on the basis of the chaotic time series，which can provide a new practical method to forecast the surrounding rock displacement of underground powerhouse system.

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DYNAMIC MONITORING AND SIMULATION ANALYSIS OF SURROUNDING ROCK DEFORMATION OF TUNNEL IN KARST REGION

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2008, 27 (S2): 3816-3816 doi:

[PDF] 557 KB (1214)

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Because of the influence of karst caves，deformation characteristics of surrounding rock of tunnel in karst zone are different from those of common tunnel. Taking Baoshiyan tunnel in Dacheng high-speed railway as an example，the deformation characteristics of surrounding rock of the tunnel with a karst cave at side is studied by field monitoring and by finite difference software ，and the deformation characteristics of the surrounding rock of tunnel are obtained by field monitoring and by simulation analysis，which are mostly consistent. Results indicate that after the tunnel is excavated，the surrounding rock moves toward the karst cave and the tunnel. The surrounding rock between the karst cave and the tunnel deforms in opposite direction，and it is also the most dangerous zone. The displacements of the surrounding rock of the tunnel¢s representive positions near the karst cave are larger than those positions away from the karst cave，and the horizontal displacement of the left side wall is twice bigger than that of the right side wall. With the increase of the karst cave dimension，the settlement increment of the crown is the largest，and the horizontal displacement increment of the side wall is moderate and that of the hance is the least. The subsidence of the karst cave top and the horizontal displacement at the right position are larger，and those of other positions are little. Because the deformation of the surrounding rock of the tunnel appears unsymmetrical，deviation pressure will occur during excavation. The conclusion can be useful in design，construction and research of similar tunnels.

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BACK-ANALYSIS AND APPLICATION STUDY ON SURROUNDING ROCK PARAMETER FIELD OF UNDERGROUND ENGINEERING

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2008, 27 (S2): 3822-3822 doi:

[PDF] 216 KB (1189)

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The quality of rock mass become unfavorable by the influence of blasting explosion，opening and lag of anchorage and support. The closer the surrounding rock near cave surface is，the worse it becomes. The longer the time after opening without anchorage and support is，the worse it becomes. So it is thought that surrounding rock is heterogeneous，but a parameter-field of space distribution，which is varied with the geological conditions；and opening and support methods are presented. Adopting 3D elastoplastic damage FEM and displacement back-analysis method，the proper parameters of surrounding rocks are determined by sensitivity analysis. Adopting local cross section model，the local parameter-field can be calculated rapidly. Then，the parameter-field of whole 3D model can be built by interpolation. Finally，combined with Pubugou underground powerhouse，the 3D FEM model is built. When monitoring data are inputted，the surrounding rock parameter-field can be obtained. The calculation results are used to predict the displacement and stabilization of surrounding rock. The results show that the distribution of parameters of surrounding rock mechanics calculated agrees well with those measured.

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STUDY ON PRE-REINFORCED HALF-TUNNEL STRUCTURE IN HIGH CUT SLOPE

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2008, 27 (S2): 3827-3827 doi:

[PDF] 250 KB (1153)

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The pre-reinforced half-tunnel has been proposed as a new construction method to protect the environments in highway 306 of Tibet. This method combines pre-reinforcement of the high slopes with prestressed cables and half tunnel excavation. With this method，it is possible to reduce much excavation earthwork，and at the same time，to keep the whole slope stable. The behaviors of the pre-reinforced cables，however，have not been investigated extensively. An assessment is therefore needed for the effectiveness of various reinforcement designs of the half-tunnel with pre-reinforced structure. In this paper，the background and objective of this study are first presented. Then，a numerical method and the analysis procedure are briefly described. The numerical simulation include：(1) an unreinforced case；(2) one role of pre-reinforced cables in the top rock mass；(3) two roles of cables in the side wall；(4) one role of cables in top rock mass and one role in side wall；and (5) one role in the top rock mass and two roles in side wall rock mass. The commercial code FLAC2D is adopted to execute the numerical analysis，in which the behavior of rock mass is described by Mohr-Coulomb constitutive model and the prestressed cables are simulated by an internal structural element of FLAC2D code. Finally，the effectiveness of the pre-reinforcement for the half-tunnel excavation and design of pre-reinforcement are discussed based on the numerical results and suitable retaining scheme is presented.

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ANALYSIS OF FOCAL MECHANISM CAUSED BY RUPTURE
OF STOPE ROOF

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2008, 27 (S2): 3833-3833 doi:

[PDF] 278 KB (944)

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As a regional，real-time and dynamic monitoring means，the microseismic monitoring technology is quite feasible to forecast several geological hazards，such as rockburst，mine tremor，coal and gas outburst，and so on. And because of the good expandable nature of this technique，it even can prevent and reduce these disasters. The study on the focal mechanism of different hypocenters or seismic sources is the prerequisite and basis for forecasting rockburst by microseismic monitoring technology. Roof structure，especially hard and thick sandstone roof，is one of the main factors leading to the occurrence of rockburst. Based on the analysis of the fracture of hard roof，the equivalent point source model of the tremor or rockburst caused by hard roof is Constructed. According to the model，the seismic displacement equation of hard roof is analyzed by using seismic wave theory. Based on the above analysis，the focal mechanism caused by the rupture of roof is pointed out. The microseismic signals of the fracture of hard roof acquired by the microseismic monitoring system in Sanhejian Mine validate the theoretical analysis results. The results show that by the tensile strength of medium nearby the seismic source，the wave field will generate compression wave in the seismic source and induce tensile fracture at the moment of rock breakage，which is different from the style of failure in the coal pillar and fault. The results can be used to provide theoretical basis to forecast and prevent rockburst caused by hard roof.

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STUDY ON FORECAST AND PREVENTION METHODS FOR ROCKBURST OF DEEP ROADWAY WITH HIGH GEOSTRESS

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2008, 27 (S2): 3840-3840 doi:

[PDF] 287 KB (1233)

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Forecast and prevention methods were studied for rockburst in haulage-dip at Coal Mine No.12，Pingdingshan Coal Group of China. This haulage-dip belongs to a deep roadway with the complex geological conditions，and the tectonic stresses are very high. The surrounding rock of the haulage-dip is a typical brittle rock with high strength and is a middle burst-prone mine. The in-situ monitoring results for rockburst with electromagnetic emission method(EEM) were basically consistent with practical situation. The critical value of EEM was 30 mV and the critical value of pulse count was 400 000. When the magnitude of EEM in the roadway area exceeded the critical value，the rockburst occured in this danger area of haulage-dip. After the shallow blasting measures were taken；the pressure over roadway roof was released，and the magnitude of EEM obviously decreased. The intensity and frequency of rockburst were also reduced. Therefore，rockburst can be effectively prevented. Short-range excavation，bolt supporting with shotcrete in-time and hanging steel net during roadway excavation can reduce or lessen the hazard of rock burst.

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FBG传感器在量测围岩内部位移中的应用

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2008, 27 (S2): 3847-3847 doi:

[PDF] 249 KB (1476)

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The most important advantage of fiber Bragg granting(FBG) sensor is the wavelength-encoded information given by the Bragg grating，since the signal from Fiber Bragg granting sensor immunes to power fluctuations，optical fiber bend loss，optical fiber connection loss along the optical path. Fiber Bragg granting sensor can be used to measure many different parameters including strain，temperature，stress，displacement，etc. Based on displacement monitoring of new Austrian tunneling method(NATM)，this paper describes the principle and application of fiber Bragg grating sensor in surrounding rock internal displacement monitoring. Comparing with other methods，this measurement method is an excellent and practical method which has the advantages such as simple instrument architecture，easy installation，convenient measurement，accurate measured data. The FBG sensor has been applied to the practical engineering. The measured data proved that：the relaxation deformation of surrounding rock will change along with the change of location，the relaxation deformation descends slowly when the depth from excavated surface increases；the integrity level of surrounding rock has great effects on its internal displacement.

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IN-SITU STRESS FIELD OF COAL AND GAS OUTBURST
MINING AREA

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2008, 27 (S2): 3852-3852 doi:

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The hollow inclusion technique is used to measure the in-situ stress of coal and gas outburst mining area. The measurement sites lie in the Northeast，Middle and East China，which include 7 mining areas such as Fuxin，Pingdingshan，Hebi，and Huainan. Based on the analysis of measurement data from outburst mining areas，conclusions could be drawn as follow：(1) major principal stress and minor principal stress are horizontal stresses and the inter medium principal stress is vertical stress，and the type of stress field is the dynamic stress field；(2) the major principal stress and minor principal stress are higher than those of other regions；and the tectonic stress is outstanding；(3) the ratio of major principal to minor principal stress ranges from 1.56 to 3.93，in which 69% ranges from 1.7 to 2.8 and 50% is about 2.0；the subtract of major principal stress and minor principal stress is very salience；(4) the ratio of the major principal to the vertical stress decreases with the increase of depth. The stress field has the changing tendancy from dynamic to static. At last，the role of in-situ stress is discussed. The gas and coal strength are the main factors influencing coal and gas outburst. Gas pressure and gas content increase in high in-situ stress environment，so the impetus of coal and gas outburst increase. Because the coal strength(peak strength) decreases，so the resistance of coal and gas outburst decreases. As a whole，in high in-situ stress environment，the gassy coal tends to be instable and coal gas outburst occurrs as a result. In-situ stress plays a key role during the occurring and development of coal and gas outburst. The characteristic，of in-situ stress fields have an important function in coal and gas outburst.

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ANALYSIS OF DOUBLE-LAYERED LINER BEHAVIORS OF SHIELD TUNNEL UNDER ACTIVE MOVING GROUND-FISSURES

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2008, 27 (S2): 3860-3860 doi:

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The shield tunnel under the environment of moving ground-fissures will bear additional stress and deformation which are larger than those of normal condition when subjected to the relative moving of ground-fissures. so，the tunnel-lining will lose the function both in the aspects of strength and watertight. In this paper，a kind of double-layered lining which casts an integral reinforced concrete internal lining inside duct pieces，is developed to co-bear the additional loads and reduce the stress and deformation of structures. Numerical analysis is performed to analyze the double-layered lining behavior of stress and deformation subjected to the actions of ground-fissures. The relative moving distance，the strength and thickness of inner lining are the main influencing factors，and some conclusions with guiding significance to practical engineering are drawn. The results show that the integral reinforced concrete internal lining inside duct pieces can effectively reduce the stress and deformation of the tunnel-lining；the stress and deformation of the lining has linear proportion with the relative distance of ground-fissures；the thickness of the internal liner has great impact on the stress and deformation of the lining，and the stress and deformation of the lining become smaller when there is bigger thickness of the internal lining，but when the thickness of the internal lining exceeds 300 mm，there only exists weaker influence with the increase of the thickness；The strength of inner lining has smaller impact on the stress and deformation of the liner，and in the specific engineering C30 concrete is enough.

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NUMERICAL SIMULATION OF EFFECTS OF DOUBLE-TUBE
PARALLEL SHIELD TUNNELING ON NEIGHBORING BUILDING

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2008, 27 (S2): 3868-3868 doi:

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It is a crucial problem to ensure the safety of the superstructure and underground tunnel construction in urban district，especially for tunneling beneath the building with thin overburden soil layers. Based on Wuhan Yangtze double-tube parallel shield tunneling project，3D numerical simulation of the effects of double-tube parallel shield tunneling on a neighboring 5-story building with reinforced concrete frame structure，through which the shield tunneling will cross，is studied by finite element program ABAQUS. The spatial distribution of the ground settlement is investigated. The settlements observed in the field are consistent with numerical simulation results. The deformations of soil and buildings，which are induced by shield tunneling，can be predicted and analyzed.

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STUDY ON DISTRIBUTION REGULARITIES OF DISC CUTTER THRUST FORCE FOR SHIELD TUNNELING

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2008, 27 (S2): 3875-3875 doi:

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Shield machines have been widely used in tunnel constructions recently. When a shield machine is driving，its cutter head is pushed on tunnel face and complex interactions between disc cutters and tunnel face will be induced. In order to study the distribution law of thrust force of each cutter，influencing factors on the interaction are analyzed firstly. Rock strength and stiffness are the main factors during shield driving. On the hypothesis of elastic and point contact between cutters and rocks，the mechanical model of three-dimensional elastic supports is developed and is simplified. Acting forces on the disc cutters are calculated by finite element method(FEM)，and are compared with the results of simplified mechanical model. Thrust forces of the disc cutters are not uniform on the cutter head. The thrust forces of some disc cutters，where the disc cutter is rare，are higher than those of the others. The thrust forces of face cutters are 40%–60% higher than those of marginal cutters on the cutter head. For the same cutter head style，the thrust forces distribution vary obviously with different cutter layouts. Finally，the effects on thrust force distribution of disc cutters by rock stiffness are analyzed using Monte Carlo FEM. The softer the rock is，the more uniform the disc cutters¢ thrust force is，and vice versa. When the shield is driving in hard rock，those disc cutters of high thrust forces are heavily abraded and need be replaced frequently. This will bring negative influences on the shield performance. The layout for these disc cutters on the cutter head should be improved in the future.

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EXPERIMENTAL STUDY ON FAILURE BEHAVIOR OF ROCK CONTAINING THREE-DIMENSIONAL SINGLE PRE-EXISTING FLAW

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2008, 27 (S2): 3882-3882 doi:

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The investigation on the brittle failure behavior of rock mass containing flaws is one of the important research fields of solid mechanics，especially in rock mechanics. It is also significant for engineering and academic studies. An experimental method for investigating three-dimensional failure process of rock containing three- dimension pre-existing flaws is proposed. By employing this method，the three-dimensional failure behaviors of basalt specimen containing single pre-existing flaw with different angles are investigated. The following experimental results have been drawn. (1) Failure surface and peak strength of rock mass containing 3D flaw are influenced directly by propagation direction and volume of flaw. (2) For rock containing 3D flaw，the ratio of yield strength to peak strength equals 0.75–0.82，and average value is 0.78；the ratio of residual strength to peak strength equals 0.58–0.67，and average one is 0.63. For intact rock，the ratio of failure(residual) strength to peak strength has little changes.

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RESEARCH PROGRESS IN THEORY AND FORMING CONDITION OF LOCALIZED DEFORMATION BANDS IN HIGH-POROSITY ROCK

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2008, 27 (S2): 3888-3888 doi:

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Recently，localized planar zones of deformation have been discovered in high-porosity rock，which are called compaction bands，shear bands and dilation bands. It is one of the most concerned issues in the research of rock physical and constitutive relations. The research of localized deformations has practical significance in the storage of water，oil，nuclear wastes，the disposal of garbage and environmental pollution. It is also helpful for the research of geological structure，engineering geology，and engineering of soils and rocks. The compaction band and shear band theories，based on localized bifurcation，are introduced. The conditions for band formation and discrimination in porous rocks and the critical hardening modulus for compaction bands，shear bands and dilation bands are also introduced. The compaction bands and shear bands on an elliptic yield cap are introduced based on the cap model. They are close related to the s-e curves. Under low confining pressure，the first zero modulus point，i.e. the shelf，corresponds to the compaction band，or the volumetric yield surface of cap model. When loading continues，the s-e curve keeps ascending until the sample hardens. The second zero modulus point in the s-e curve，i.e. the peak of the s-e curve，corresponds to the shear failure，or the shear yield surface of the cap model. Mass experimental results obtained from axisymmetric compression tests on sandstones with different grain scales and porosities can be described by the same cap model.

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DISCUSSION ON MECHANICAL PROPERTY AND UTILITY OF WEAKLY WEATHERED ROCK MASS FOR ON YANGTZE RIVER XIAONANHAI HYDROPWER PROJECT

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2008, 27 (S2): 3899-3899 doi:

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Xiaonanhai Hydropower Project is the third large grade I hydropower project on Yangtze River. Its rock foundation is composed of typical red beds，which have been weathered and demarcated clearly. The average thickness of the overburden and strongly weathered zone is 18 m，and the average thickness of the weakly weathered zone is about 6 m. If all the weakly weathered rock masses are excavated，the excavating depth will be equal to one third of the total one. Obviously，the excavating volume is huge. The wave velocity distribution of rock mass in a large area of dam site，engineering classification of rock mass quality，deformation and strength properties of rock mass are analyzed. The differences between weakly and slightly weathered rock masses are researched，and the probability of using the weakly weathered rock mass as foundation plane is discussed. The experimental results of this stage show that the qualities of weakly and slightly weathered rock mass are grade IV，the mechanical parameters of weakly weathered rock mass approach to those of slightly weathered rock mass，and the weakly weathered rock mass can be used as foundation plane.

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ANALYSIS OF STRUCTURE STABILITY AND REINFORCEMENT
BASED ON DEFORMATION REINFORCEMENT THEORY

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2008, 27 (S2): 3905-3905 doi:

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The concept and rationality of using plastic complementary energy(PCE) as the criterion of structures¢ stability are illustrated. Based on the concept of constraint-equilibrium in non-equilibrium thermodynamics，deformation reinforcement theory，which analyzes the mechanical behaviors of unstable structure with unbalanced forces exceeding the yield surface，is presented. Compared with the results obtained by ABAQUS，TFINE and theory respectively，the stabilities of cylinder rock specimens and homogeneous slope are analyzed. The influence of mesh sizes of the dam-heel in FEM on PCE is studied based on Drucker-Prager yield criteria. By adopting the load with the same magnitude but in opposite direction with unbalanced forces，the bearing capacities of rectangular column and strip foundation before and after reinforcement are analyzed and compared with the theoretical solution. The results show that PCE is the scalar norm of plastic strain from the perspectives of integral degree，as well as the distance away from safety. Hence PCE could be a reasonable evaluation criterion of structure. Furthermore，the reinforcement calculation and analysis based on unbalanced forces clearly present the area and size of reinforcement under a certain safety degree. This type of reinforcement is very efficient and could provide guidance for practical engineering.

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STABILITY CONTROL METHOD OF DEEP ROCK TUNNEL AND CASE STUDY

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2008, 27 (S2): 3913-3913 doi:

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FAST BACK ANALYSIS OF REASONABLE TENSILE TONNAGE OF PRESTRESSED ANCHOR CABLE IN UNDERGROUND ENGINEERING

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2008, 27 (S2): 3919-3919 doi:

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Recognized as an important way to ensure the stability of underground chambers，prestressed anchor cables are widely used in underground engineering. There is an initial stress after the prestressed anchor cable is installed，and the stress varies with the consequence of excavation. How to select an appropriately initial tensile tonnage to make the stress of prestressed anchor cable reach the designed stress so as not only to exert the effect of prestressed cable but also to preserve a certain of safety margin is an important issue. The issue is converted to an optimization problem on reasonable tensile coefficient of prestressed anchor cable. Firstly，stress calculation theory of prestressed anchor cable is introduced. Then，the optimal self-adjusting variable-metric algorithm using difference coefficients and imprecise linear search is proposed and applied to inversion of reasonable tensile coefficient of prestressed anchor cable. The algorithm improves the conventional variable-metric method by using self-adjusting variable-metric method based on Broyden¢s family to update metric matrix，makes different coefficients approach gradient and imprecise linear search method find optimal step length. At the same time，by using incremental variable plastic stiffness matrix method，reassembling stiffness matrix is avoided when prestress is modified，consequently computing speed is improved. A case study is given at last，which proves that the algorithm¢s superiorities of super-linear convergence，less computation，and better numerical stability.

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EXPERIMENTAL STUDY ON CREEP BEHAVIORS OF GREENSCHIST SPECIMEN FROM JINPING II HYDROPOWER STATION UNDER BIAXIAL COMPRESSION

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2008, 27 (S2): 3928-3928 doi:

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The biaxial compression creep tests on greenschist specimens from auxiliary tunnel of Jinping II Hydropower Station were carried out. There were many kinds of loading paths and many different stress levels in the tests. The one-dimensional Burgers model was developed into biaxial compression state. And the creep parameters of greenschist under biaxial compression were determined by Burgers model. The results show that the loading path has important effect on the axial and lateral creep laws. If the axial and lateral loads are exerted simultaneously with fixed ratio，the axial and lateral strains will ascend with increasing axial and lateral stresses. But if the axial load is exerted gradually with fixed lateral stress，the lateral strain will descend with increasing axial stresses. The comparison between Burgers model and experimental curves shows that Burgers model is applicable for determining the viscoelastic rheological parameters of greenschist. These parameters are helpful for the design of deep cavern of Jinping II Hydropower Station.

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FINE STRUCTURE DESCRIPTION FOR FRACTURED ROCK MASS AND NUMERICAL TESTS ON ITS ENGINEERING PROPERTIES

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2008, 27 (S2): 3935-3935 doi:

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The randomicity of fractures¢ shape(fracture orientation，dip，trace length，width，and spacing) and distribution are considered，and Monte Carlo technique is adopted to develop a code RFNM. By RFNM，not only the virtual fractured rock mass，in which the structure information of fractures is described and the real engineering rock mass is represented，can be generated，but also the fractured rock mass model can be discretized and then combined with numerical methods to solve practical engineering problems. Therefore，the virtual fractured rock mass with random fracture networks is in fact one digital fractured rock mass model. In addition，FEM is adopted to develop the GeoCAAS(geo-engineering computer aided analysis system) code. The mechanical and hydraulic properties of fractured rock mass are studied by numerical tests. The results provide the evolutionary laws of deformation modulus and permeability with the increase of fracture trace length. Furthermore，the relationship between deformation modulus and permeability is discussed.

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THREE-DIMENSIONAL CONNECTIVITY RATE AND SHEAR STRENGTH PARAMETERS CALCULATION BASED ON A NEW MODIFIED METHOD OF MEAN TRACE LENGTH

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2008, 27 (S2): 3941-3941 doi:

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Connectivity rate of discontinuities in rock mass is an important parameter as a reflection of the joints¢ extendible extent and connectivity status，which is also a key factor of estimating the shear strength parameters of fractured rock mass，as well as the precondition of rock slope stability. A calculating method for three-dimensional connectivity rate of rock mass discontinuities has been presented based on 3D network simulation，and its application to shear strength parameters estimation is also discussed. A new technique to estimate the mean trace length in sampling windows by considering the general probabilistic distribution of trace length and obvious decline of discontinuities is suggested using probability statistic method. The estimated mean trace length has been used to construct 3D discontinuous network model of rock mass from the entrance of the diversion tunnel of Yujianhe Hydraulic Project in Guiyang Province. The precision of the model is improved. Based on the constructed 3D network model，the values of 3D connectivity rate in different cross-sections have been figured out by slice method and then they are used to estimate the shear strength parameters of the simulated rock mass through weighted average method. The results show that the anisotropy of rocks in this area is quite obvious and the connectivity is well-developed. The planes with tendency of 70°–80°and inclination angle of 20°–40° are dangerous cross sections，in which the maximum connectivity rate is 0.914 3 and the minimum cohesion and internal friction angle are 1.135 MPa and 25.7° respectively，therefore，more attentions should be paid to engineering construction.

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INFLUENCE OF EXCAVATION FORM OF ROCK SLOPE ON DEFORMATION AND STRESS OF FITTING-SLOPE
CONCRETE FACE ROCKFILL DAM

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2008, 27 (S2): 3950-3950 doi:

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In order to use rockfill dam¢s adaptable predominance over topographical condition，and to reduce the excavation volume of overburden under the dam，concrete face rockfill dam(CFRD) designed on the strip mountain ridge is filled fitting the natural side，which makes the original massif be parts of the dam body，thus a fairly rare fitting-slope CFRD is achieved. Stress concentration tends to happen in the contact zones between rock slope and rockfill material，and the displacement of downstream part of dam is usually great，which usually leads to slipping of fitting-slope CFRD and to the decrease of the safety of CFRD. A new idea，ledge excavation of rock slope，is suggested to solve this complex problem. Comparison between the stress-deformation behavior of dam with ladder type rock slope and that of dam with line type rock slope has been made by using two-dimensional finite element numerical analysis. The calculation result shows that the displacement of dam with ladder type rock slope is much less than that of dam with line type rock slope. So ladder type rock slope is probably reasonable，especially for fitting-slope CFRD. At last，the influence of angle of excavation slope on dam¢s deformation and stress is discussed.

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PRELIMINARY STUDY ON DAMAGE-HEALING MODEL UNDER EARTHQUAKE

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2008, 27 (S2): 3956-3956 doi:

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The damage and failure of brittle media are challenging and complicated issues in mechanics field. Earthquake is a kind of typical failure or instability of brittle medium. Taking earthquakes for example，some precursory phenomena can be observed before the occurrence of catastrophic failure，and the healing phenomenon will take place gradually after earthquakes in a long time. So the study on the damage-healing process of the earth crust media is very significant to earthquake prediction. The model of damage rheology proposed by V. Lyakhovsky is introduced at first，and the shortcomings of the model are analyzed using the data obtained by acoustic emission experiment of rock failure. Secondly，based on damage mechanics，Helmholtz free energy，considering the healing phenomenon of the earth crust media，a new damage-healing model is set up in one dimension，and the damage-healing pattern is calculated with numerical method. The damage-healing process of the media is simulated under load which consists of two parts，the constant loading rate and a sinusoidal perturbation，to simulate solid tidal stress；and the evolution of load/unload response ratio(LURR) during the damage-healing process is also investigated at the same time. The result shows that the LURR value successively experiences，i.e. abnormity appearing，rising to the peak value then decreasing sharply before the occurrence of the catastrophic failure. This result validates that LURR can describe the damage degree of materials quantitatively and is a good forecast of catastrophic failure，which also can provide solid basis for LURR method in physics.

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STUDY ON TESTING IN REINFORCED SLOPE WITH HOLLOW GROUTED BOLT

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2008, 27 (S2): 3963-3963 doi:

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The hollow grouted bolt can improve grouting pressure by hollow bolt bar. Contrast has been done between hollow grouted bolt and full-length bonded one in reinforcing high slope of K60+535–K60+585 of road S246 in Xin¢an county，Luoyang City，Henan Province. There is limestone in this area，and joint develops strongly. There are two kinds of bolt in reinforcing the slope. Analysis has been done according to grouting pressure，grouting volume，the maximum tension force and the displacement. The maximum value is 181 kN for the hollow grouted bolt，and the full-length bonded one is 183 kN in the common fractured areas，but in the strongly fracture areas the maximum values is 179 and 153 kN，respectively. And the distributions of axial and shear force in the bolt are analyzed by the UDEC software.

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HIGH SLOPE FUZZY NUMERICAL ANALYSIS OF XIANGJIABA HYDROPOWER PROJECT

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2008, 27 (S2): 3968-3968 doi:

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Vague information always exists in mechanical parameters of rock mass in geotechnical engineering. The vague uncertain information of each physical variable is treated as fuzzy numbers in the control equation of finite element during the calculation. The calculated results of fuzzy finite element are also fuzzy numbers. Stability of the artificial high slope in the left bank of Xiangjiaba Hydropower Project is analyzed with the program based on fuzzy finite element method. Influence of fuzzy characteristics of mechanical parameters on the distribution of fuzzy stress and displacement is also studied. It shows that fuzzy characteristics of mechanical parameters in the artificial high slope in the left bank of Xiangjiaba Hydropower Project results in great extent variation of tensile stress area. It is suggested that the influence of variation of tensile stress area on the slope reinforced extent should be considered in the design for the reduction of engineering risk.

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STUDY ON CREEP CHARACTERISTICS OF REGULAR ROCK MASS DISCONTINUITY

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2008, 27 (S2): 3973-3973 doi:

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Creep characteristics of rock mass discontinuity is very important in solving the practical problems in rock mechanics. Rheological characteristic of rock mass discontinuity is one of the most important mechanical characteristics of rock mass. It controls the creep transfiguration and long-term strength. Through the shear test of dentate discontinuity on the condition of two-axes stress，this paper studies the creep characteristics of discontinuities with different slope ratios and normal stresses. By fitting and analysing the test data，the rules among normal stress，shear stress，slope ratio and creep of shear direction，normal direction and also the time-depended rules are discussed. Burgers model is used to describe the creep characteristics of discontinuities. Based on the model test，a 3D FEM program is used to analyze the mechanical properties of rock discontinuities with regular dentations during loading. Through the finite element analysis，the stress distribution of the rock mass discontinuity is studied. The failure model is discussed by the creep model test and finite element analysis；and the tension force is supposed to be the key factor for the failure of discontinuity.

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SIMPLIFIED MODELS IN ESTIMATING DEFORMATION MODULE OF ROCKS BY USING DEPTH-DEPENDENT PERMEABILITY

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2008, 27 (S2): 3980-3980 doi:

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In geotechnical engineering，it is difficult to determine micro-mechanical parameters of large-scale rock mass. However，the depth-dependent permeability，due to coupling of seepage field and stress field in large-scale rock mass，suggests a chance to solve the problem. According to the hydro-mechanical coupling behaviors of rock mass under geostatic pressure，simplified models in estimating deformation module of rocks by using depth- dependent permeability is developed. Porosity and opening of rock fractures are applied to the transition factors in deriving equations for bulk modules of intact rock and normal stiffness of joints. The models is limited with assumptions such as the rock mass is relatively uniform，containing one group of joints and without tectonic stress. However，the assumptions are not serious limitations in suggesting this new way to determine micro-mechanical parameters of large-scale rock mass.

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STUDY ON INFLUENCE OF FAULTS ON GEOSTRESS BY MEASUREMENT DATA AND NUMERICAL SIMULATION

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2008, 27 (S2): 3985-3985 doi:

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Taking one oil region in the northern Songliao Basin as engineering background of the research，the geostresses of the two oil layers in four boreholes have been measured by the methods of differential strain analysis(DSA) and anisotropic of wave velocity. The results reveal that there exist considerable differences between the geostress states of four boreholes which are only 2 000 m away from each other，and especially the differences of orientation. The analysis of affecting factors on the geostress states show that the differences are due to the influence of faults. With the aid of three-dimensional finite element simulation techniques and the theory of optimization，analysis of the distribution of geostresses in the study area has been carried out by the secondary development of ANSYS. It is found the heterogeneity and aeolotropism of geostress states are caused by faults or superposition of action of faults. The results show that the deviation in the orientation of the maximal horizontal stress exists in the adjacent zone of the faults，and the deviation angle near the end of the fault is more than 40°. So the distribution of the geostresses can not be generated by limited discrete measuring points. The 3D numerical simulation is an effective method for geostresses research.

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APPLICATION OF RADIAL BASIS FUNCTION NEURAL NETWORK TO COMPREHENSIVE EVALUATION OF DAM SAFETY

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2008, 27 (S2): 3991-3991 doi:

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The methods of multi-step grey-correlation evaluation and fuzzy comprehensive evaluation are usually used in dam safety evaluation. Both of them need to design weights of each index and membership of evaluation indexes，and then the dam safety is determined synthetically. Due to the complexity and diversity of each problem，the subjective factors have great influences on the final evaluating conclusion. The artificial neural network could adjust the weights of each influencing factor automatically. It could not only absorb the experts¢ thought and experiences embodied in the study samples，but also possess high anti-jamming ability and better error permissibility. As a result，an improved BP neural network has been applied to comprehensive evaluation of dam safety. However，the shortcomings of slow convergent rate，poor stability and local minimum of BP neural network have extremely restricted its application. Therefore，the radial basis function neural network is proposed to apply to comprehensive evaluation of dam safety. By study of the given samples，the experts¢ knowledge，experiences，subjective judgment and tendency towards the importance of objectives embodied in the samples are obtained. When applying the well trained network to map a new input of given samples，the output results can reproduce the experts¢ instinctive thought and experiences and make a reasonable evaluation conclusion. Evaluation examples of ten typical dam sections of Fengman dam testifies the validity of the new method.

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EXPERIMENTAL STUDY ON FAILURE MODE OF
CLAYEY SOIL

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2008, 27 (S2): 3998-3998 doi:

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In order to study the failure mode and the load bearing mechanism of the strip foundation，one model test based on the similarity theory has been designed to simulate the clayey subsoil. On the one hand，the soil pressure of the subsoil and the diversity have been measured，and the distribution rule has been analyzed together. On the other hand，the shear belt formation and the developing process have been observed. The results show that the model test is an important means to understand the mechanical characteristics，such as the subsoil deformation to destruction，the subsidence distortion characteristics，the true stress distribution and variation law，which has theoretical significance in studying the subsidence distortion characteristics as well as the destruction shape and mechanism of the deep excavation.