Strength thresholds of crack initiation ( ) and crack damage ( ) of hard rock are of great significance not only for understanding the progressive failure process and brittle failure mechanism but also for establishing the crack initiation strength criterion and long-term strength criterion. In view of this, four methods to calculate the crack initiation and damage strength, including crack volumetric strain model, acoustic emission method, lateral strain and volumetric strain observation method, moving point regression technique, are summarized systematically; and marble and granite in uniaxial stress state are taken as examples to show problems in determining and by each method. Results show that and can be obtained conveniently and precisely through crack volumetric strain model which has a clear physical meaning; progressive failure and damage process of rock can be comprehended qualitatively or semi-quantitatively by analysis of acoustic emission hit rate; but and can not be acquired accurately. Curve of volumetric strain stiffness is strongly influenced by data intervals and characteristics of different stages during loading are not obvious when moving point regression technique is used, which makes the determination of difficult. The result could contribute to understanding the importance and calculating methods of crack initiation and damage strength thresholds and provide a useful reference to choose appropriate calculating method.

Through analyzing the salt rock deformation under triaxial compressive stress condition, the large compressive deformation properties of salt rock under higher confining pressure are shown. The problems of the axial stress-strain obtained by axial load divided by the initial cross-sectional area of the specimen are pointed out for triaxial compressive tests. Thus the engineering strain and logarithmic strain are analyzed and compared; and the applicable conditions of these two strains are explained. Finally, the triaxial compressive tests for different confining pressures are carried out and the test results are compared. The research results shows that the logarithmic strain should be used to analyze the large deformation property and the modification of axial stress for salt rock when the larger deformation occurs. The deformation obtained by logarithmic strain and engineering strain for salt rock could be expressed as a linear function of confining pressure. When the confining pressure is 20 MPa, the axial compressive deformation is 3.09 times that of 5 MPa. The higher the confining pressure is, the larger difference of the maximum axial stress is between obtained by the initial cross-sectional area and the logarithmic strain corrected area, and the latter is less than the former. When the confining pressure is up to 20 MPa, the maximum axial stress for the logarithmic strain correction area is only 63.85% of that for the initial cross-sectional area.

An layered earth model, a pile foundation load model, a shallow tunnel excavation model and an associated support model, together with plane strain model test system for measuring pile foundation load, soil pressure, soil settlement, and support strain are set up. Experiments are conducted to study the influences on soil pressure redistributions, soil set, tunnel crown settlements, and internal forces of the tunnel support caused by a nearby shallow tunnel excavation under the condition of various horizontal and vertical existing pile foundation loads. Moreover, the test process and different working conditions are simulated via the FLAC3D software. The results are as follows: (1) Compared to the tunnel excavation without pre-existing pile foundation loads, pre-existing pile foundation loads can significantly alter the soil pressure redistributions, soil settlements and internal forces of the tunnel support; (2) For pile foundation loads of different length, fixed pile diameter and horizontal position, when the ratio of pile length and tunnel depth is equal to 1.0, it causes a largest influence on the effect of tunnel excavation, in the case of the ratio less than 1.0, the influence decreases with the decrease of the ratio; when the ratio is beyond 1.0, the influence of the pile length change on tunnel excavation effect becomes smaller. (3) For file foundation loads of fixed pile diameter and length, the soil pressure, ground settlement and internal force of tunnel support increase with the decrease of the relative horizontal distance between the pile foundation loads and the tunnel. If the ratio of horizontal distance between the pile foundation loads and the tunnel and tunnel diameter is from 0.5 to 4.0, the tunnel will be in the danger. If the ratio of that is from 4.0 to 6.0, the influence on tunnel caused by the pile foundation loads will become lighter. If the ratio of that is beyond 6.0, the influence can be neglected.

In order to study the creep properties of salt rock under low frequency cyclic loading, creep tests on salt rock samples under low frequency cyclic loading are carried out by adopting the loading mode of cyclic confining pressure with a constant axial stress. The test results show that up to a certain time, the axial creep curves of salt rock are smooth; while after that point, the axial creep curves clearly fluctuate with the confining pressure. Overall, the axial creep curves of salt rock under low frequency cyclic loading are similar to that of Burgers model. According to the connection relation of component creep model, the Burgers model is divided into Maxwell model and Kelvin model. The axial creep equations of Maxwell model and Kelvin model under the loading mode of cyclic confining pressure with a constant axial stress are deduced respectively in the superposition condition that the fatigue failure of material is neglected, and the effect of loading cycle on the models are also analyzed. Then, by combining the axial creep equations of Maxwell model and Kelvin model, the axial creep equation of Burgers model under cyclic loading is obtained; and the reasonability of which is verified by using the creep test data of salt rock. The result indicates that fitting curves and test curves conform well each other; and the proposed model can well reflect the creep properties of salt rock under cyclic loading, especially the fluctuation of creep deformation with loading change.

A theoretical methodology which can calculate multiple scattering of plane SH waves by arbitrarily arranged and configuration of multi-row tubular piles is achieved. It can be considered the commonly so-called single scattering as the first order of multiple scattering. The second order of scattering of certain tubular pile is derived from incident waves which are excited from the first order of scattering by all tubular piles, which are also be regarded as the secondary waves by the first scattering. The rest scattering process of multiple order can be considered in the same manner. Assuming that every scattering order at pile-soil interface and interior of tubular pile are satisfied the elastic boundary conditions, the incident, scattering and transmitted waves are expanded in wave functions with Graf’s addition theorem so that the undetermined scattering (transmitted) complex coefficients are obtained. Theoretical solutions of total scattering and transmitted wave fields inside the tubular piles are achieved. The influences of multiple scattering orders, ratios of the pile radius and distance between piles (or pile rows), shear modulus ratios of pile and soil, ratios of internal and external radius of tubular piles, geometric parameters of multi-row tubular piles etc. on screening effectiveness is discussed with numerical examples. The results show that tubular piles can achieve better screening effects than solid piles do. Several valuable reference bases of engineering design with discontinuous barriers made by tubular piles are delivered consequently.

To obtain the effects of varied saturations and confining pressures on mechanical properties of sandstone, the triaxial tests on sandstone samples from Balikun mine were performed under varied saturation and confining pressures. Then the modulus, peak strength and residual strength were obtained. The effects of varied saturations and confining pressures on mechanical properties of Balikun’s sandstone were analyzed; and the results show that: (1) With confining pressure increasing, the sandstone modulus increases, and the relationship between confining pressure and modulus follows linear form. With saturation increasing, the modulus decreases. The uniaxial compression modulus of saturated sandstone decreases 50.9%. The relationship between saturation and modulus follows linear or negative exponential form. (2) With saturation increasing, the peak strength decreases. The uniaxial compression strength of saturated sandstone decreases 44.2%.The relationship between saturation and peak strength follows natural logarithm form. (3) The effects of confining pressure on residual strength can be described by degradation index. The relationship between degradation index and confining pressure of Balikun sandstone follows negative exponential form. With saturation increasing, the residual strength decreases. (4) With confining pressure increasing, the effects of varied saturation on modulus, peak strength and residual strength decrease. (5) Less than 60% of saturation, variation of saturation greatly influences the modulus and peak strength. Larger than 60%, the effects decrease. Less than 80% of saturation, variation of saturation greatly influences residual strength.

In triaxial loading and unloading tests of soft rock, the determination of compressive strength is a critical problem, which always tends to use empirical method，while less corresponding standards at present. Based on this, a set of triaxial loading and unloading tests of sandy mudstone were carried out and the experiment results show that: (1) Sandy mudstone samples always show obvious strain hardening characteristics in both triaxial loading and unloading tests when the confining pressure is more than 10 MPa. (2) The mechanical response differences of sandy mudstone under triaxial loading and unloading tests are obviously, the samples always have only one macro shear failure surface in triaxial unloading tests; while the samples have no obvious control fracture surface under the condition of triaxial loading, and the dilatancy effect is obvious. (3) The semi-log method was introduced into the data analysis of soft rock triaxial loading and unloading tests, which can determine the compressive strength more conveniently. (4) Based on the analysis of stress and strain increment in the process of triaxial loading and unloading tests, the deformation and failure process of soft rock can be divided into three stages: smooth stage, rule jump stage and sharp jump stage; the division has obvious physical significance, which can be used as an important reference for determining the compressive strength. Therefore, the two methods can be integrated used to determine the compressive strength of soft rock in triaxial loading and unloading tests. The methods for determining the compressive strength is very applicable, and can also provide reference for similar soft rock tests.

Liquid nitrogen has an extremely cold temperature, which is between -195.56 ℃ and -180.44 ℃. When it contacts rock, it can make the rock pore structure damage. Based on this characteristic, cryogenic nitrogen can be used as fracturing fluid to fracture the formation. In order to research the effect of cryogenic nitrogen on pore structure damage, two kinds of sandstone samples are selected. These samples are frozen with cryogenic nitrogen at different original degrees of water saturations. Porosity and nuclear magnetic resonance characteristic of all samples are measured before and after experimental test. With the assistance of nuclear magnetic resonance (NMR) technique, porosities, transverse relaxation time T2 distributions and T2 spectrum areas of all samples are obtained. The results show that rock pore structure is damaged by cryogenic nitrogen freezing and the degree of damage is related to rock type, porosity and original degree of water saturation etc.. With the growth of water saturation, the degree of damage increases. Especially, when the degree of water saturation is 100%, obvious cracks appear in the samples. The form of pore structure damage is mainly the growth and development of micro-pore, which can cause the connectivity of the porous structure improving and promote the appearance of new pores with larger radius in specimens. Thereby, it cause serious damage on pore structure.

The stress state of rock mass is very complex in practical engineering; it’s not just a simple loading or unloading; such as the dams of hydraulic engineering, considering from its mechanical condition, the dam foundation excavation main shows the unloading at the direction of excavation (other directions may be unloading or loading); after construction of the dam , it main shows loading from the mechanical condition, so it has an important engineering significance to study the mechanical properties of rock mass’ reloading after a unloading damage. The results show that: the confining pressure for intermittent jointed rock deformation modulus has little effect; the elastic modulus of rock has no apparent relationship with the confining pressure; jointed rock mass deformation modulus and elastic modulus are significantly lower than intact rock under the same confining pressure: jointed rock peak strain increases linearly with the confining pressure; and there is a good correlation between the two. Compared to the intact rock samples, joint rock the peak strain of jointed rock grows faster with confining pressure increasing. The lower the confining pressure is, the greater of the impact of unloading on rock strength is. With confining pressure increasing, different of damage caused by different unloading amount of rock samples will decrease.

A series of experiments of slope rainfall erosion were done in laboratory for steep loess slope with slope angle of 70° under a rainfall intensity of 2.7 mm/min. According to the characteristics of slope erosion, the evolution of rainfall erosion process is generally concluded as splash and sheet erosion in earlier phase, rill erosion in middle phase, and finally evolved into gully erosion and collapse in later phase. It was found that the degree of erosion at the slope top is stronger than other positions during the experiment; after a through gully formed on the slope surface, the water flow then began to scour soil inside the gully; with rainfall lasting, the strength of the soil around the gully obviously decreased; consequently collapse took place at the slope top and eventually caused wholly demolition of the slope. Based on the experiment, simulating the slope erosion process with PFC3D with fluid-soil coupling method, observing the large deformation of particles, simultaneously the microcosmic parameters such as particle motion trace, porosity and water flow rate in fluid cells are obtained; from their quantitative change process, the distribution of degree of erosion and erosion intensity of water flow in slope is got; it indicated that the degree of erosion and the erosion intensity of water flow at slope top are strongest and both reduced as the height decrease, which is consistent with the indoor model experiment.

Fourteen groups of slate samples are selected to take the mineral ingredient and microstructure test and make the lateral restraint swelling experiment and study the swelling characteristics and micromechanism of soft slate, taking slate form Zhijiang, Huaihua in Hunan province for example and considering the internal structure of soft slate and its swelling characteristics with water. The results indicate that the relationship between the lateral restraint expansion ratio and water absorption time exhibits exponential function. In the early stage of test, the expansion ratio increases with the extension of water absorption time; the growth rate is fast; and expansion ratio-time relationship curve is relatively steep. At the end of the test, the expansion tends to be stable; and the shape of the curve becomes from steep to gentle. The relationship between the expansion ratio and water absorption rate exhibits the power function. In the early stage of test, the growth rate is fast with the increase of water absorption rate, and gradually becomes lower until it tends to be stable in the late period of the test. The axial expansion rate greatly decreases in the form of logarithmic function with the increase of the axial load in the early stage of test, and gradually becomes stable in the late period of the test. When the angle α between the soft slate structural plane and axial direction changing from 0° to 90°, the expansion ratio reduces with the increase of angle α.

The extraction of methane hydrate in the seabed will result in a series of geotechnical engineering problems and disasters. In order to ensure the safety of the related engineering facilities during the extraction, it is necessary to build reasonable constitutive model for methane hydrate bearing sediments. Based on the thorough study of the geomechanical characteristics of hydrate bearing sediments and the contacts between soil grains, the authors suppose that the geomechanical behavior of hydrate bearing sediments resulting from the combination of the friction between soil grains and cementation due to methane hydrate. Considering the different mechanical mechanisms of the friction and cementation, the modified Cam-clay model and elasticity damage model are employed to describe their mechanical responses respectively. By assuming that soil skeleton and cementation have the same strain during the loading, a constitutive model coupling elastoplasticity and damage for methane hydrate bearing sediments is then established based on a simplified damage evolution law. The calculated results are compared with the experimental data of methane hydrate bearing sediments with different hydrate saturations. It is shown that the proposed model can describe the stress-strain behavior of methane hydrate bearing sediments quite well, which demonstrates the validity and reasonability of this model.

Based on summarized results of several large-scale soaking tests, some new recognition about methodology of collapsibility evaluation and reasonable limit of remnant collapse are proposed to modify difference between computed collapse under overburden pressure and measured value, and to decrease the collapsible loess treatment depth. When acquiring the computed collapse under overburden pressure, a depth correction factor? is suggested to make computed collapse under overburden pressure and the computed collapse of laboratory tests approximate measured collapse of in-situ tests; and it will decrease remnant collapse of collapsible loess in deeper position in some degree. When obtaining computed collapse, a scheme amplifying coefficient threshold of collapsibility (0.015) is presented, the method combined with depth correction factor? can reach the expected goal to enlarge the computed collapse and decrease remnant collapse of deeper collapsible loess. The conception “critical collapsibility depth” of dead weight collapse loess with heavy section is proposed; the critical collapsibility depth is set as 20-25 m temporarily according to some test data. In combination with the method of depth correction factor and amplifying coefficient threshold of collapsibility, the conception of critical collapsibility depth can decrease effectively remnant collapse of collapsible loess. The research results will be of interest for similar projects in the area of dead weight collapse loess and be useful to revise “standard for building construction in collapsible loess regions”.

The information of the in situ stress is stored in the rocks after excavation. The deformation rate analysis (DRA) method is used to determine the in situ stress based on the rock deformation memory effect(DME). Cracks generation and propagation under the previous load was initially assumed to be the mechanism of the rock DME. However, this mechanism can not explain many phenomena in the rock DME. The lack of a theoretical model prevents the correct interpretation of experimental data and improvements of the DRA method. The physical experiment is firstly performed on a volcanic sediment sample. It is showed that the in situ stress in the low stress region can be determined by both the axial strain and the lateral strain, while the DRA curves by these two kinds of strain are same. Then, the frictional sliding over the crack interfaces and grain boundaries in rocks are proposed as the mechanism of the rock DME in the low stress region. Based on this mechanism, a theoretical model using elastic element viscous element and St. Venant bodies is constructed. Cyclic compressions with different peak stresses and delay time are performed on the theoretical model. Results show that, not only the formation of the rock DME is well explained but also many DME phenomena are observed, such as the memory fading and the accuracy of the DRA curve by the lateral strain as the same as the axial strain. All the results by the theoretical model are in accordance with the experimental results. By the theoretical model, the frictional sliding over the crack interfaces and grain boundaries is verified to be the mechanism for the rock DME in the low stress region. Moreover, the results by theoretical model provided a basis for the improvement of the DRA method in the determination of the in situ stress.

When coal is recovered by mining, or fluid recovered or injected, complex interactions of stress, gas sorption and thermal expansion have a strong influence on the mechanical and transport properties of coal. In this study, intact coal with endogenetic gas, collected from Baijiao mine and Zhangshuanglou mines in China, were treated by thermal-mechanical loading under different isothermal conditions. A special apparatus is used to measure mechanical parameters of solid and gaseous products released from specimen. It is observed from thermal deformation-time curves of the coals that both the deformation of coals and associated gas desorption are significantly controlled by applied thermal conditions as expected. The results show that Baijiao coals with highly in-situ gas content tend to swell below 35 ℃. And above 35 ℃, the coals first swell and then shrink. For Zhangshuanglou coals with lowly in-situ gas content, the coals exhibit swell, followed by shrinkage of coal matrix under isothermal conditions below 60 ℃. However, the coals tend to expand on the whole when the isothermal conditions are set above 60 ℃. The results indicate that the coal deformation is dominated by competition between thermal expansion and shrinkage of coal solid by the applied temperature. Meanwhile, more thermal-induced desorbing gas flow into pores and cleats of the coal. In this case, the stressed coal is characterized by complex coal-gas interaction under different isothermal conditions. Existing pore gas may be squeezed out during initial compaction of pore and cleat of coal. Ebb and flow of desorbing gas is observed from elastic deformation to failure. In comparison with the data of the two coal samples, both uniaxial compressive strengths and Young’s modulus of the coal samples are found to deteriorate with increasingly temperature conditions. It may help us to gain an insight into temperature dependency of mechanical property of gas-bearing coal.

Toppling failure is one typical type of deformation failure modes of steep layered rock slopes. Analysis of toppling failure of rock slopes due to seismic loads possesses an important guiding significance for engineering design. Based on the limit equilibrium, a general analytical solution of block toppling failure due to earthquakes is presented for the condition that block slenderness is relatively large. In terms of cases with simple geometry, explicit expressions are given. The calculation formulas of the normal force between block interfaces, failure mode transition point and toe residual sliding force are obtained. The influence of seismic loads on the failure mode of counter-tilt rock slope, maximum allowable inclinations of the line normal to dip when toppling failure occurs, failure mode transition point and toe residual sliding force are studied through four typical examples. Those provide a theoretical foundation for the seismic support design of counter-tilt rock slopes. Finally, the comparative analysis of the analytical method and the transfer coefficient method is done according to the quantitative relationship between seismic influence coefficient, failure mode transition point and toe residual sliding force. The results show that the analytical method achieves sufficient accuracy when block slenderness is more than 20.

To provide the reference for secondary utilization of the heavy metals contaminated soil washed by EDTA (Ethylene Diamine Tetraacetic Acid), batch tests are conducted to determine the permeability, water holding characteristics, deformation characteristics, and shear strength of lead contaminated soil after washing remediation by EDTA with different concentrations. And X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests are conducted to reveal the mechanism of changes on the engineering characteristics. Results show that pH of the washes soil decreases from 7.94 to 5.12, hydraulic conductivity decreases by more than one order of magnitude, cohesion reduces by more than 50% and void ratio decreases from 0.813 to 0.764 as the concentration of EDTA increased from 0 to 0.15 mol/L, but the internal friction angle and water holding capacity increase. XRD test results show that the mineral content of montmorillonite (from 7.87% to 0.07%), illite, albite decrease and quartz increases by 11.09%. MIP test results show that the total void volume reduces as the concentration increasing, and the amount of intrudes mercury per unit mass decreases from 0.22 ml/g to 0.15 ml/g. Research results indicate that it is imperative not only considering about the removal rate of heavy metals in soil and economic index of the remediation engineering, but also the weaken soil engineering properties brought by the process of washing remediation.

Bentonites have been widely adopted as the buffer/backfill materials for repositories of high-level radioactive waste disposal. Characterization of the effective thermal conductivity of the buffer materials is of great importance for optimization design and safety assessments of the repositories. Using the concept of the series-parallel structural models, the porosity of soils is decomposed into two components: one in parallel and the other in series connected to the solid phase. An effective structure depends on the decomposition is introduced to describe the heat transfer process of the porous soils considering the structural connections of pores and the solid phase. On this basis, four formulas which represent different series-parallel arrangements of pore fluids (water and air mixture) are proposed to predict thermal conductivity of unsaturated soils with a comprehensive consideration of the effects of mineralogical composition, porosity and saturation. An effective model for thermal conductivity of unsaturated soil is then developed based on a linear composition of the four formulas. Parameterization of the model is discussed; and the behaviors of the model with respect to the variations in porosity and saturation are illustrated. The model is validated against experimental data of thermal conductivity of MX-80 and Gaomiaozi bentonites. The results show that the arrangement of air and water in the pores tended to be in parallel connection for unsaturated bentonites because of the fine size and wettability of the soil particles. This research may provide a helpful reference for predicting thermal conductivity of unsaturated bentonites and numerical modeling of the coupled thermo-hydro-mechanical (THM) processes in the engineered barrier systems.

Generally, curves of rock creep include three stages: attenuation creep stage, steady creep stage and accelerated creep stage. The traditional models for rock creep, which always contain Newtonian dashpot rather than non-Newtonian dashpot, couldn’t describe accelerated creep stage. An improved constitutive model for rock creep is proposed; and the method can be divided into three steps. First, traditional Kelvin model is not quantitatively good in description of initial attenuation creep stage and steady state creep stage. A modified Kelvin model using non-Newtonian dashpot is used here in. The power-law creep function is obtained by solving the constitutive relation. Second, the parallel connection of non-Newtonian dashpot and plastomer, whose creep function is power function, is used for description of accelerated creep. Third, by connecting instantaneous elasticity Hooke body, modified Kelvin and nonlinear viscoplastic body in series, a new visco-elastoplastic constitutive relation of rock is proposed. This creep model can describe attenuation creep stage, steady-state creep stage and accelerated creep stage. It is shown that creep testing curves under different conditions are coincident well with the theoretic curves; and the model is reasonable and feasible.

The existence of various types of joints, one of the typical characteristics of prefabricated lining structures, makes the mechanical performance of shield tunnel linings quite different from that of monolithic linings. A simplified calculation method for the dynamic elastoplastic analysis of segment lining subjected to explosion seismic wave is proposed. The lining is composed of a number of rigid arch segments that are interconnected by elastoplastic hinges. The stiffness contribution of joints and the dynamic interaction between the structure and the soil can be properly simulated with the method. As an example, the calculation of the shield section of Nanjing metro subjected to explosion seismic wave is discussed. Meanwhile, the influences of incident wave angle, rock grade and the depth of the segments on dynamic response of tunnel lining are taken into account. The result indicates that the angle of the incident waves plays an important role on the tunnel lining, where the dynamic response to obliquely incident and explosion seismic wave is larger than that to vertically incident and explosion seismic wave. The higher the surrounding rock grades, the better the capacity to resist deformation of liner structure and the better the blast-resistant characteristics of the tunnel will be. The increase of the depth of the segments would lead to notable increase of the internal force, the blast resistant characteristics could be improved by properly setting the depth of the segments.

The breccia, a typical unfavorable geologic body in Wudongde hydropower station with low strength, poses a potential threat to the stability of underground cavern in left bank. Firstly, physico-mechanical properties of breccia, as well as the strength, cementation with limestone, dolomite and marble, and fusing contact characteristics are obtained by in-situ investigation and borehole television, and experiments in laboratory. Following that a 3D numerical simulations, which consider the left hill and underground cavern and are suggested mechanical parameters, are performed to simulate the excavating of main powerhouse for revealing the mechanical responses of breccia in roof during excavation. The simulated result provides useful information for detail design of rock supporting by showing the calculated failure approach index. The responding supporting design including the prestressed rock bolt, shotcrete and prestressed anchor cable. In-situ practice involving rock excavation and reinforcement indicates that the breccia in the roof remains stable, which is also confirmed by in-situ monitoring deformation with convergence pattern. This analysis indicates that the breccia can be adopted as load bearing rock in view of the acceptable self-stability and compressive strength related to the diagenesis process. Detail excavating and supporting schemes which utilizes the relaxing-inhibition supporting idea are applicable and practical.

As a kind of vertical anchoring technique, the anti-float anchor has been widely used in China, whose performance has begun to receive more attentions from researchers. However, steels may be eroded easily by groundwater or chemical solutions, which will cause the reductions of mechanical strength and service life, especially in subway engineering the steel anti-float anchor is forbidden. Glass fiber reinforced polymer (GFRP) anti-float anchor is a new kind of material which is composed of resin matrix and glass fiber. Compared with steel anchor, the GFRP anti-float anchor has higher strength, corrosion-resistance and light weight behavior. The field tests show the feasibility of GFRP anti-float anchor through embedded bare fiber optics sensor technique. According to the test results, the GFRP anti-float anchor stress-strain behaviors, load transfer mechanism and failure mechanism are considered. The test indicates that GFRP anti-float anchor is basically about shear failure and pullout capacity of anchors with ? 28 mm are 250 kN, which can be satisfied with engineering demands. The axial forces of anchors fall gradually with depth, and it will not bear load beyond certain length. Results show that the effect distance of axial forces is about 3.7 m when the length of bond part is in range of 3.95~6.95 m in moderately weathered granite，which indicates that GFRP anti-float anchors also exist critical anchorage depth. The shear stress on interface of anchor is not evenly distributed, which peak value is being driven down, and so as to the zero value. The research results can provide evidence for application of GFRP anti-float anchor.

In west China, a certain number of mining areas are in the mud weakly cemented soft rock strata; these soft rocks have the properties such as poor cementation, low strength and mudding when encountering water. Rectangle is a common pattern of mining roadway, but the wall rock stress is nonuniform and its stability is poor. In the soft rock strata, the rectangular roadway bearing capacity is low, and deformation is large and will last for a long time; these bring great difficulties for the safety of coal mine production. The belt crossheading rectangular tunnel of the new Shanghai No.1 coal mine in Inner Mongolia is taken for example, the rectangular tunnel deformation and failure are simulated through the Cvisc viscoelastic plastic model of FLAC3D. The simulation results are compared with in-situ monitoring values. The results show that: Influenced by cross-section shape, compressive stress concentrate in the four corners, zone of tensile stress is significant in the roof, roof subsidence is big, the floor heave and sides deformation are serious. Influenced by surrounding rock lithology, surrounding rock mass plastic zone is bigger and it causes support structure is difficult to fully play the effect, and surrounding rock appears the phenomenon of whole sliding. In addition, the deformation of surrounding rock exhibits rheological deformation characteristics, deformation quantity increases with time, continuous creep deformation is beyond the controllable limit of support body, eventually causes the instability and failure of the tunnel.

Based on the engineering case of a pipe-jacking working shaft sunk with the aid of caisson jacks in soft clay, the construction technology is presented and the effects on surrounding environment are studied. According to analysis of the soil mass and pipeline monitoring data during the jacked sinking process, some conclusions are drawn as follows. The jacked open caisson construction method can control the attitude of the open caisson and stabilize the sinking speed effectively; but it also squeezes the soil. At the preliminary stage of open caisson sinking, the compacting effect is significant and the excavation effect becomes more notable as the open caisson sinking deeper. The subsurface horizontal displacements and surface settlements grow along with the increase of the sinking depth H. The ground surface settlement profile is of spandrel type with an influence zone of 1.7H. Among layered settlements the unit settlement of the soft silty clay is the largest. The pipeline settlements are controlled in the millimeter level. Based on data fitting of the dimensionless surface settlements, an empirical method either in the form of exponential function or bilinear curve to predict the ground surface settlement caused by jacked open caisson construction is proposed, which is verified through two case studies.

Research on rebuilding prediction of bank slope during the operation of reservoir is one of the important and hot topics in engineering geology field. In light of defects of Kachugin method applied to bank collapse prediction on soil bank slope including using semi-empirical, semi-quantitative model, simplifying the influence of hydrogeological conditions and ignoring the effect of wave erosion on bottom of bank slope, a modified Kachugin method based on wave cut notch and critical height of soil is put forward. Estimation method for stability time limit of soil bank slope rebuilding is established. Limit equilibrium method and Kachugin method and the bank slope rebuilding prediction method are used in bank collapse prediction of Baima harbor bank slope at Fengjie in the Three Gorges Reservoir. The calculation results show that the result of modified Kachugin method is small than one by other two kinds of prediction methods; and the deviation is less than 8.05m . Based on reservoir bank geological survey at present, it is consistent with the truth one. Research results have important positive significance for land resources development and utilization in bank area and prevention and mitigation of reservoir bank.

Based on the measured data of surrounding rock pressure and deformation in the segment of Longxia Railway at Xiangshan extra-long tunnel that is buried deeper than 500 m with high development of geological structure, studied the characteristics of surrounding rock pressure, formation mechanism of the deformation pressure, etc., in the segment of the deep tunnel with high development of geological structure are studied. The research shows that: in the deep segment of tunnel, large deformations happen in the sections with lots of structure planes, folds, reversed faults and little ground water, after the excavation, even though the surrounding rock strength is higher. The larger surrounding rock deformation is contributed by the opening and volumetric dilatancy of the structural planes, which are compacted by the self-weight stress and residual tectonic stress, as the lateral confinement is eliminated after the excavation. For that, great deformational pressure from the surrounding rock may be exerted to the primary support. The surrounding rock pressure in the above segment has the following characteristics: (1) The surrounding rock pressure is greater in the sections with little ground water than the sections with a lot. (2) The surrounding rock pressure largest on the arch crown to the hance in the sections with syncline that developed in the tunnel longitudinal, the nearer to the core of the syncline, the greater the pressure. (3) In the sections developed with folds, the surrounding rock pressure is larger in the direction perpendicular to the fold axis. (4) In the sections developed with reversed fault, the surrounding rock pressure is larger in the side that opposite the fault dip; and the surrounding rock pressure in the position of fault surface is largest in this side, smallest in the other side. (5) The surrounding rock pressure on the lower bench is smaller than that on the upper bench, the longer the time between the excavations, the greater the difference between the pressure.

The dynamic unloading effect should be considered when tunnel or cavern is excavated by drilling and blasting method under high in-situ stress; and its damage zone forms will eventually be affected by multiple factors. By using three-dimensional finite difference software FLAC3D, the distribution of surrounding rock damage zone induced by the coupling effect of blasting load and dynamic unloading is discussed; then the influences of lateral pressure coefficient, the mechanical properties of rock mass and the unloading rate on damage range of surrounding rock are taken into account in the analyses; and finally through the excavation damage zone detection data of Meihuashan Tunnel of Gan-Long Railway in Jiangxi province. The results of numerical simulation are verified. Researches show that the rock damage zone under the coupling effect of blasting load and dynamic unloading is significantly greater than that only considering the blasting load; dynamic unloading of in-situ stress can not be ignored. As the lateral pressure coefficient increases gradually, the damaged zone presents the obvious directivity, when the lateral pressure coefficient is 1, the damaged zone will uniformly distributed along the excavation contour surface, and when the lateral pressure coefficient is not 1, the damage zone will mainly concentrate in minimum principal stress direction. The better rock mechanical properties is, the smaller the damage zone will be. The faster the unloading rate, the larger the damage zone of surrounding rock will be; but the impact is not significant. The results provide suggestions for stability analysis of tunnels under high in-situ stress and supporting design of the cracked surrounding rock.

Dahongshan iron mine which uses sublevel caving method without sill pillar has three extra-large mined-out area, the displacement of overburden and surface subsidence will lead to ground pressure and geological disasters, like rolling stones in open stope, air-blast wave in the underground stope, mud-rock flow in surface and underground, and so on. In order to monitor the natural caving height and displacement of overburden and subsidence range and displacement of surface, we use many means of monitoring methods, like multi-channel microseismic monitoring system, non-contact displacement monitoring system, handheld GPS device, total-station instrument. We obtained a lot of data after two years of monitoring; these data show that the natural caving height of overburden is between 1 090 m and 1 060 m elevation, the total settlement of observation point in +1 090 m tunnel is 1 350 mm, the subsidence range of surface is within the scope of the designed surface displacement based on traveling angle 75°, the maximal total vertical and horizontal displacement in surface is 1 779 mm and 948 mm, the deformation of overburden and surface is stable and controllable, there is no disaster occurred at present.

Continuous deformation happened in Shuping landslide, since the impoundment of the Three Gorges reservoir from 2003. It is necessary to study the deformation and failure mechanism of Shuping landslide, in order to evaluate and predict the stability of landslide. The field geological survey and exploration are used to determine the form and property. The deformation characteristics of the landslide are analyzed in detail to make full use of monitoring data. The deformation mechanism and influence factors of landslide are studied based on investigation and monitoring; and the stability of landslide is calculated and predicted. Survey and analysis results show that, the geological factors, included topography, lithology and geological structure, control the deformation. The reservoir water fluctuation and rainfall trigger the deformation of Shuping landslide. Indeed, the relationship between slope groundwater fluctuation and reservoir water fluctuation primarily affected the deformation, especially during the decline process of slope groundwater with the drawdown of reservoir water. Because decline speed of groundwater is much slower than that of reservoir water, it increases the hydraulic gradient and seepage force in the landslide body apparently, and then reduces the slope stability, increases the landslide deformation rate especially when the sharp decline of reservoir water level. In addition, if the long-term or intensive rainfall occurs during the drawdown of reservoir water, more obvious deformation will happen and landslide might be failed. So the engineering control measures should be carried out.

In light of that the progressive deformation of pile-soil system is not taken into account in the determination of bearing behavior of pile at present, field test and theoretical analysis are used to analyze the bearing mechanism of single pile considering progressive failure of pile-soil system. Firstly, the skin friction degradation and end resistance softening are analyzed using field test results; and then the softening models of skin friction and end resistance are proposed. Furthermore, determinations of the parameters related to the softening model of skin friction and end resistance are presented, and the reliability of the proposed models is demonstrated. As to the bearing behavior of a single pile considering progressive failure of pile-soil system, a highly effective iterative computer program is developed using the proposed softening model. Comparisons of the load-settlement response demonstrate that the proposed method is generally in good agreement with the field-observed behavior, and can assess the failure characteristic of skin friction and end resistance. For practical purposes, different load transfer functions of skin friction and end resistance can be selected in the proposed iterative computer program to capture a single pile response at different loading levels.

This paper focuses on the basal stress distribution and depression of stress of sand prism. The sand prism is divided into a stress known zone I and a stress unknown zone II based on the fixed principal axes (FPA) assumption. On several shear stress distribution assumptions, the stress state of zone II is available. The values of coefficient of earth pressure at rest on the sand centerline on different shear stress distribution assumptions are compared to the one proposed by Kulhawy. The following results are achieved; there is depression of normal stress on the base of sand prism, and the larger of the friction angle (the denser the sand prism) is, the more the depression of normal stress is; and the larger of the depression range is; the shape of the stress distribution and minimum value of normal stress and the location of the minimum normal stress are different on different assumptions; and the assumption of quadratic distribution and cubic distribution of shear stress are most reasonable.

Three-dimensional dynamic response of a circular lining tunnel surrounded by a full-space saturated soil to a harmonic point load acting in the radial direction is investigated. The lining is modeled as a cylindrical shell of infinite length; and the soil is modeled as a saturated poroelastic medium using Biot’s theory. Two kinds of potential functions are introduced to represent the displacements of the soil skeleton and the excess pore fluid pressure; and the modified Bessel equations are utilized to obtain the expressions of the potentials function. According to boundary conditions, the analytical solutions of displacements of lining and soil and pore pressure are derived in frequency-wave number domain. Finally, the time-space domain solutions of the dynamic responses are obtained by inverse Fourier transformation. The effects of load vibration frequency and soil permeability on displacement and pore pressure responses are investigated. Numerical results show that the displacement response of saturated soil is significantly different from that of single phase elastic soil. As the load vibration frequency increasing, the displacement amplitudes of soil and tunnel decrease, while the pore pressure amplitude increases. The displacement and pore pressure amplitudes of soil decrease as the soil permeability getting better.

In light of the randomness, fuzziness and interval feature of values of geotechnical parameters, the triangular distribution functions, normal distribution functions and quasi-normal distribution membership functions are separately proposed to express the distribution of the parameter values. The methods to determine the distribution functions of geotechnical parameters and their interval values with different cut-levels are presented. And the interval values can be expressed by the boundary values of the membership functions. The boundary values of triangular distribution functions and quasi-normal distribution functions are suggested to be determined with their average values and standard deviations. The upper or lower limit of triangular distribution function boundary value can be got by the average value plus or minus two point five times standard deviation. And the upper or lower limit of quasi-normal distribution function boundary value can be got by the average value plus or minus three times standard deviation. Then the fuzzy point estimate method is proposed to analyze the fuzzy reliability of slope engineering. The results show that the slope fuzzy reliability index determined by eleven cut-levels are approximately equal to the probabilistic reliability index got by the Monte Carlo method. The number of cut-levels is proposed to be nine. And the cut-levels can be selected from 0.1 to 0.9. The fuzzy point estimate method with the determined boundary values of different distribution functions can be used to evaluate the slope fuzzy reliability; this method is simple and practical.

Structure-foundation dynamic interaction plays an important role in the earthquake response analysis and safety assessment of structures. A novel computational model for structure-foundation dynamic interaction in the time domain based on the scaled boundary finite element method is presented. The near field bounded domain is modelled by the subdomains of the scaled boundary finite element method; and the far-field unbounded domain is represented by the high order transmitting boundary. By using the continued-fraction expansion and introducing auxiliary variables, the dynamic equation of the bounded domain is expressed in high order static stiffness and mass matrices. The high order transmitting boundary can exactly satisfy the radiation boundary condition at infinity. This open boundary is global in space, local in time and converges rapidly as the order increases. The high order transmitting boundary is based on the improved continued-fraction solution for the dynamic stiffness matrix of the unbounded domain; and the equation is a system of first-order ordinary differential equations in the time domain. Then the standard equation of structure-foundation interaction in the time domain is obtained by combining the dynamic equations of the bounded and unbounded domains, which can be solved by the Newmark method directly. The results of three numerical examples demonstrate that the proposed method is more accurate and efficient than the viscoelastic boundary in the time domain.

In order to obtain an accurate calculation of settlement after construction of soft soil foundation by vacuum preloading, surcharge preloading and vacuum combined surcharge preloading method, stress changes of soft foundation reinforced by the different preloading method is analyzed. Elasto-viscoplastic model which the specific stress path of change is weakened represents stress-strain relation of soft clay. Combined with classical Biot consolidation theory, the finite element method of calculation the settlement of the soft clay improved by preloading method is deduced. The proposed method is verified through the concrete example. The outcomes as follows: (1) Reinforcement mechanism and stress paths are not the same for the different preloading methods. Surcharge preloading method is an anisotropic consolidation process under positive pressure. Vacuum preloading method is the isotropic consolidation process under negative pressure. (2) elasto-viscoplastic model is a rheological model not affected either by transient stress or the specific influence of stress paths. It have superiority when applied it to the soft foundation reinforced by the different preloading method that neither need to consider stress paths nor need to consider the primary and secondary consolidation division. (3) In the Biot consolidation theory, using the elasto-viscoplastic model to reflect the physical equations of soft soil, consolidation settlement and settlement after construction of soft foundation could be accurately calculated. (4) The vertical displacement of soft soils is influenced obviously by viscosity parameter ? /V and plasticity parameter ? /V of elasto-viscoplastic model.

Effects of the interface characteristics between geogrid and soil and joint protuberance on the geogrid performance are investigated by three-dimensional discrete element method. To simulate the protuberant joint, minor particles are introduced; so that the pull-out test of triaxial geogrid with joint protuberance can be modeled thoroughly. Through analyzing the shear dilatancy effect of the interface between geogrid and soil, the inherent relationship between strength (macroscopic) and fabric anisotropy (microscopic) is revealed; meanwhile, the improvement of geogrid performance attributed to the protuberant joint is also proved. Numerical results show that larger deviation can be found between the curves of Fourier coefficient and pull-out force. In terms of the development of strength (macroscopic), its accuracy can be obtained via considering normal contact force and fabric evolution coefficient which reflects the degree of anisotropy. Moreover, with the existence of protuberant joint, the internal force distribution of longitudinal rib can be homogenized; larger relative displacement between geogrid and soil will be allowed; and the material properties could be well performed. The research results can provide reference for optimizing the geogrid reinforcement performance microscopically.

The nonlinear volumetric increase of rock masses can influence the safety of tunnel excavation; thus it is important to accurately evaluate the dilation mechanism of surrounding rock masses in the plastic zone. However, most of the existing studies solve the stress and strain states in strain-softening rock masses of deep circular tunnels by using the constant or linear dilation model. In order to overcome this deficiency, based on the finite difference method, a new analysis approach is proposed. It can consider the nonlinear dilatancy effect as well as the strain-softening behavior of surrounding rock masses. Moreover, the calculated results are compared with those from other existing methods to verify the calculation accuracy of the proposed method. And then a further study is made to investigate the influence factors of the dilatancy coefficient in the plastic zone with different qualities and support pressures of limestone rock masses, and to compare deformations of surrounding rock masses by the constant and nonlinear dilation models. The results indicate that: for rock masses with lower value of geotechnical strength index (GSI) and poor quality, the confining stress primarily controls the degree of the dilation in the plastic zone; and the deformations at the opening surface with constant and nonlinear dilation models distinguish greatly.

The underground gas storage in salt caverns, mined by drilling and water dissolving solution, has low visibility and high difficulty of cavern form controllability, so it is a very significant measure to carry out scientific stability evaluation on deformed gas storage for ensuring its safe operation. In this study, the variable weight theory and relative difference function are introduced to build the assessment model which can be suitable for salt cavern stability assessment. Based on the sonar data of salt cavern shape, the 3D model is built up firstly in numerical simulation calculation, and the simulation results are used as the marking standard of relational assessment index. This model is applied to the stability assessment process of some salt cavern in Jintan; and improving measures for safety are carried out on the basis of assessment results. By a comparison of these results with some others, it is shown that the stability assessment model is more reasonable, as the evaluation index weight has been recalculated by variable weight theory; and this method has relatively better applicability in cavern stability assessment of gas storage in salt cavern.

Sedimentary rocks such as shale and sandstone are very common in the fields of oil and unconventional gas drilling; and they are often characterized by orthotropy. The extended finite element method is used for crack propagation analysis of orthotropic rock mass and a Matlab program Betaxfem2D has been developed. Asymptotic crack tip displacement fields deduced by function of complex variable method are adopted as the crack tip displacement enrichment function; and mixed mode stress intensity factors are calculated by the interaction integral (M-integral) method. Besides, a modified maximum circumferential tensile stress criterion is adopted to determine crack propagation direction. Compared with conventional finite element method (FEM), the results show that the extended finite element method needs less DOFs and less computer resources to achieve the same calculation accuracy. The extended finite element method program developed by this paper and the conventional FEM program are used to simulate the 4-point bending test of rock sample, and both of them show the same results. Numerical experiments show that crack propagation direction angle ? varies according to an approximate sine function with a period of π with the increase of α, i.e. the angle between the orthotropic material coordinate and the space coordinate. Besides, when shear modulus and Poisson ratio remain constant; the range of the sine function shrinks with the decrease of the ratio of the elasticity moduli E1 /E2, but the phase basically remains unchanged. So, the orthotropy of rock cannot be neglected when dealing with the fracture mechanics problems of sedimentary rock.

There are many failure modes in the foundation pit engineering. Considering the correlation between failure modes, the range of system failure probability is large using the Breadth Border method or the narrow bounds method. The response surface is established by using the uniform test and nonparametric regression method. On this basis, in order to obtain the index of each failure mode, the random parameters generated by the Monte Carlo simulation are interpolated. Combined with the Pearson correlation coefficient, the correlation is tested between failure modes. Considering the correlation of multiple failure modes, the system reliability analysis method of foundation pit engineering based on conditional probability is put forward. As a typical example, a system failure probability of foundation pit is analyzed by using the conditional probability method. A case study shows that the method is simple and reliable in calculation, so as to provide a new way for the system reliability theory of foundation pit.