Concrete-rockfill combination dam (CRC dam) is composed of concrete wall, rockfill, cushion layer and transition layer. As a new structural pattern, its stress and deformation characteristics are not studied thoroughly. For this reason, a model test is carried out to measure the earth pressure and displacement of CRC dam on alluvium deposit at different heights and to explore the performance of CRC dam in filling and impoundment stage. Then a modified calculation method of earth pressure considering the displacement is proposed. The test result shows that: the rockfill is close to active state at the end of dam filling construction, the earth pressure on the concrete wall is relatively low, while the rockfill is close to static state under the water pressure at the end of impoundment stage, the earth pressure on the concrete wall is approximately one time higher than that of the filling stage. The modified formula well reflects the change rule of the earth pressure with wall displacement during filling and impoundment stage. The minimum of sliding safety factor (SSF) occurs at the end of dam filling period and meets the relevant requirements. The test proves that the CRC dam has good adaptability to alluvium deposit.

To investigate mechanical parameters of fine-grained sandstone after high temperature, X-ray diffraction, scanning electron microscope (SEM) and uniaxial compression tests are conducted on fine-grained sandstone samples after 400~1 000 ℃ heating treatment. The correlation among mineral composition, structure characteristics and mechanical parameters of samples and temperatures is analyzed. The results show that: the polycrystalline occours in the fine-grained sandstone after high temperature treatments. Within 600 ℃, quartz content in the sample increases with increasing temperature, crystal diffraction enhances, and melting and recrystallization phenomenon can be observed clearly when the temperature is 600 ℃. Above 600 ℃, quartz content reduces with increasing temperature, the intensity of crystal diffraction is weakened, the crack quantity, the width and length increase, and cracks can be divided into the crack through the particles and along the grain boundary. The temperature of 600 ℃ is the critical temperature of quartz crystalloblast approximately. Within the range of 400 ℃ to 800 ℃, longitudinal wave velocity of the sample linearly decreases with the temperature. The sample strength is strengthened under 600 ℃, but the sample strength is weakened over 600 ℃. Thus, 600 ℃ can be used as a threshold temperature of strength conversion of samples. Within 400 ℃, elastic modulus and deformation modulus of samples increase slightly with the temperature increasing, and initial modulus and peak strain remain basically. However, deformation parameters of samples decrease with the temperature increasing above 600 ℃, and peak strain increases monotonically with temperature increasing above 400 ℃. The deformation parameters of fine-grained sandstone samples are more sensitive to the high temperature.

After the impoundment and operation of reservoirs, the repeated change of water level has “fatigue effect” on the rock mass of the reservoirs slope, and the deterioration of the rock mass under water-rock interaction will affect the stability of the whole slope. Based on these, we acquired the following results on the foundation of the trial data analyses of the immersion-air dry cycle water-rock interaction in earlier stage. According to the characteristics of stress-strain curve acquired in the process of triaxial compression test under the water-rock interaction, and in virtue of continuum damage mechanics and statistical theory, the damage effect of the immersion-air dry cycle water-rock interaction is coupled into the damage statistical constitutive model. The damage constitutive equation of sandstone under water-rock interaction is established by considering the influence of compacted section. Comparative analysis reveals that the calculated curve based on the established sectional statistical damage constitutive model conforms well to the trial curve, which means the statistical damage constitutive model can accurately reflect the damage effect of sandstones under the immersion-air dry cycle water-rock interaction. In the process of water-rock interaction, the constitutive model parameters m and F0 all diminish gradually, which reflect the mechanical characteristics of sandstones that the brittleness weakens and the macroscopic strength reduces gradually. The results of the study can be used as a reference for long-term deformation stability analysis of a large number of existing bank slopes, and the correlation analysis method can also provide reference for similar experiments.

To understand the dissolution damage mechanism of the salt cavity surrounding rock in the process of water-soluble cavitation, the high-temperature triaxial dissolution testing machine is applied to conduct tests on salt rock specimens under complex unloading conditions (i.e. unloading confining pressure, increasing axial compression) with different brine flux. It is found that the stress and dissolution influence on each other, and the damage and dissolving characteristics of salt specimens are mutually decide in the process of unloading tests. It is shown that the higher the deviatoric stress is, the greater the amount of dissolved salt rock per unit time is. The outlet concentration of brine exhibits a significant quadratic function relation with the dissolving time. The mechanical strength of salt rock is constantly reduced and its capability of deformation is enhanced under the effect of dissolving. The greater the flux is, the more obvious change trend is. Then, a model of effective dissolving area under the coupled action of stress unloading and water dissolving is set up based on the analysis of effective dissolved area in unloading and dissolution of salt rock. The variation equations of the effective dissolution area with the dissolving time and stress level are obtained respectively. An unloading and dissolving damage evolution equation is established based on the effective dissolving area. The results can provide an important theoretical and experimental basis for further analysis of damage and dissolving mechanism of salt rock.

The purpose of elastoplastic analysis for frozen wall is not only to reduce the thickness of frozen wall, but also to provide reference for the reliability design. The development of elastoplastic analysis for frozen wall is reviewed, and the elastoplastic mechanical model of frozen wall is studied based on the elastic analysis of “Baoshen” formula. The analytical solutions of the stress field and displacement field are deduced and compared with different mechanical models. Then a discriminant for the horizontal initial stress and the plastic zone radius under different yield criteria are also investigated when the frozen wall is approaching plasticity. According to engineering case studies, the critical edge pressure, the plastic zone radius and the load on elastic zone are analyzed under different initial stress levels and different yield criteria. The results show that the critical edge pressure of the frozen wall is increased by 32%, the radius of the plastic zone is decreased by 14.5%, and the load of the frozen wall is decreased by 23.3%, which provide the data support for the reliability analysis of the design of the frozen wall thickness.

The thermal parameters of loess are the important indexes in the study of loess disaster and thermal calculation, while the water content and dry density have a certain influence on the parameters. Thermal parameters of loess samples with different dry densities and different moisture contents are tested in normal temperature by using thermal constant analyzer Test Protocol Hot Disk TPS 2500S to explore the variations of thermal parameters of loess which are influenced by moisture contents and dry densities. The study reveals that: with a constant moisture content of the loess samples, the higher the dry density is, the greater the thermal conductivity, the specific heat capacity and the thermal diffusivity are. The thermal conductivity and specific heat capacity of loess samples increase linearly with the increase of moisture contents. When the moisture content is low, the thermal diffusivity increases with the increase of moisture content. When a certain moisture content is reached, the thermal diffusivity decreases with the increase of the moisture content. The thermal diffusivity tends to be stabilized with the continual increase of the moisture content of loess samples. The impact on the thermal parameters by the moisture content of loess is greater than that by the dry density of loess. In thermal engineering calculation, thermal parameters can be dynamically selected in accordance with soil moisture.

CO2 geological storage is one of the most economical and reliable techniques for reducing CO2 emission, and the understanding of CO2 reactive transport in reservoirs is critical for that. Dardis’s porous model, coupled with our previous CO2 reactive model, is presented to investigate the reactive transport in throat fractured media. According to the velocity field results, the velocity in fracture is much higher than that in matrix and it reaches the maximum value at centerline in throat. The main dissolution reaction occurs near the inlet region, and along the upper and bottom edges of the fracture. There is nearly no dissolution along the edges after downstream throat, which is mainly affected by the throat. The concentration of H+ ion in fracture and throat is higher than that in the matrix; while the higher concentration of Ca2+ ion occurs in the region of downstream matrix. And then, the comparisons among different throat positions are also made to analyze the effects of the throat position on the distribution of dissolution rate and species concentration. Finally, the fractured media with sudden reaming is simulated, and it is found that the velocity and component migration in the fracture are enhanced, which is totally contrary to the case with throat fracture. All the above results show the capability of the present model in simulating CO2 reactive transport in complex fractured media.

The bank slope soils are periodically influenced by the fluctuation of reservoir level, and its stress process can be described as multi-cyclic loading-unloading process of the effective stress in the pre-consolidation pressure range. The triaxial test of soil stress path is used to simulate the cyclic loading-unloading of soil pore water pressure, and the deformation and development laws of soil are predicted by extending the unified hardening model and modifying the loading-unloading criteria. The results show that during the cyclic loading-unloading process, the volume deformation of the soil is periodically elastic, and the shear strain is in a spiral upward trend and its increment gradually decreases with the number of cycles. During the unloading and confining pressure yielding stage, the soil deformation shows a dilatancy feature of volume expansion and a brittle trend of shear strain increase. The measured pore pressure drops dramatically and the peak intensity point occours when the shear deformation is at about 6%. The relationship between the compression curve coefficient and the number of loading-unloading is established, and the loading-unloading rules of the overconsolidated soil are modified. The extended unified hardening model can predict the deformation characteristics of the bank saturated soil under the special stress paths.

This study measures the total stress shear strength indices of unsaturated expansive soils at different water contents under drying-wetting cycles by undrained shear tests using the conventional direct shear apparatus. Specifically, the total cohesion and the total internal friction angle are obtained to reflect the undrained shear strength of expansive soils. The matric suctions of soil samples in a fixed shear plane are measured using filter papers after shearing. A model of shear strength for the entire suction range of expansive soils is established based on the results of shear tests. The model is verified by experiment. The drying-wetting cycles significantly reduce the undrained shear strength of expansive soil. The total cohesion weakening is more significant than total internal friction angle reduction. The shear strength index of total stress shows a linear positive correlation with the logarithmic values of matric suction. The shear strength of soil increases nonlinearly with the increase of matric suction, and the increasing rate decreases gradually. The findings confirm that it is feasible to investigate the shear strength of unsaturated expansive soil using the conventional direct shear apparatus and filter paper method.

A large scale shaking table test has been carried out to investigate the amplification effect of ground motion in homogeneous and complex heterogeneous sites. After that, a Fourier transform, time frequency analysis method and subsection time-frequency analysis method are combined to analyze the experimental data. By comparing the experimental results, , the peak of the time curve of the ground motion will be gradually enlarged with the increase of the height of the site when the local vibration propagates in the vertical direction. The frequency component content, the frequency spectrum of the main frequency band, and the distribution of the whole ground motion energy on the time-frequency plane will change greatly with the height of the site and the different layers. The above study concludes a series of PGA peak characteristics, spectral characteristics, distribution characteristics of energy spectrum on time-frequency plane.

In order to investigate the effect of rock proportion on the progressive failures of soil-rock-mixture slope, five static overload tests are conducted on soil-rock-mixture slope with different rock proportion. In the course of the tests, the load and displacement of the load plate that acting on the top of the slope are measured. Meanwhile, the side slope is monitored by a high-definition image capturing system. The comparison of results between particle image velocimetry(PIV) analysis and the FLAC3D numerical simulation reveals the failure process of the slope under static overload., The PIV analytic results indicates that the rock blocks affect the shear band development. Through a comparison of PIV analytic results with different rock proportion, all the slopes develop Y-shaped shear band. As the rock proportion increases in the slope, on the one hand, the shear band affected by the gravel gradually shows deflection and twists, and two propagation modes are developed in the shear zone; on the other hand, the failure mode of the slopes gradually changes from general shear failure to local failure mode with rock proportion in range of 30%-53%.

With the development of the construction technique of cast-in-place piles with vibratory sleeves driving, the cast-in-place piles have been widely used in construction engineering. But the researches on the penetration mechanism of sleeve for cast-in-place piles installed by vibratory driving are still not complete, especially the ground vibration due to sleeve driving. The paper presents a finite element and infinite element coupling model for full penetration process of sleeve installed by vibratory driving, and investigates in detail the rule and construction safety distance of ground vibration. The orthogonal finite element method is used to evaluate the influence of each factor on the construction safety distance by orthogonal test and numerical simulation. The results indicate that the ground vibrates horizontally in sleeve penetration. The horizontal peak velocity at the ground surface does not occur until the sleeve toe is on the ground surface. As the sleeve penetrates into the ground, the horizontal peak velocity occurs at a critical depth of vibration. And the horizontal peak velocity at the ground surface exponentially decays with the increasing of radial distances. Construction safety distance increases with the increase of dynamical load amplitude, soil–sleeve friction, and decreases with the increase of vibration frequency, soil elastic modulus. Furthermore, the influence of isolation trench’s filling material, depth and width on the damping effect are investigated. The results show that damping effect of open isolation trench is the best. The depth of the isolation trench has vital effect on the damping effect while the width has little effect.

Western Hubei-Eastern Chongqing region is rich in oil and gas resources, and the cap rocks are Jurassic mudstone and Silurian mudstone from top to bottom. However, this region has been suffered long term uplift and erosion, which may result in cap rock generating fractures. To investigate mechanical properties of mudstones during geological evolution, three typical tectonic mudstones deposited in the Jurassic Shaximiao formation, Tongzhuyuan formation and Silurian Longmaixi group, are selected to conduct triaxial unloading tests under five different confining pressures from 10 to 50 MPa. The results show that the unloading effect of these three mudstones is enhanced with the increase of unloading confining pressure, and the Jurassic mudstone increases in unloading deformation, the Silurian mudstone mainly exhibits the lateral expansion along the unloading direction. In comparison with the stress state of rock failure in the normal triaxial compression test, under unloading condition, the unloading strength of the mudstone and the internal frictional angle are increased. The mudstone lateral fracture coefficient is negative exponential distribution and decreases with the increase of the confining pressure. The mudstone with short sedimentary history is more prone to damage during the uplift and denudation process. The rock fracture pattern is governed by the rock structure and the stress environment. The mudstone of Shaximiao formation presents a single shear section failure, and the fracture is gentle, while the fractures of the mudstones of Tongzhuyuan formation and Longmaxi formation transit from a single shear cross section to the conjugate shear with increasing the confining pressure. The fracture of Tongzhuyuan formation mudstone is smooth, but the fracture of Longmaxi formation mudstone is jagged.

The strength characteristics of coal-rock under non-uniform distributed load are investigated using a self-developed mining-induced stress testing system under different conditions of initial vertical stresses, initial horizontal stresses and stress transfer velocity. The results show that the external damaged coal-rock block has strengthened effect on the bearing capacity of internal coal-rock blocks. When the initial vertical stress, the initial horizontal stress and the stress transfer velocity are fixed, the internal bearing capacity of coal-rock is approximately twice that of the external coal-rock. With the increase of the initial vertical stress, the later period bearing capacity of the whole coal-rock is reduced and is located in the range of different initial vertical stress. There exists a difference in decreasing characteristics between internal- and external coal-rock. When under a lower initial vertical stress range, the reduction of strength of external coal-rock in the later period is higher than that of internal coal-rock. When under a relatively high initial vertical stress range, the reduction of mechanical strength of external coal-rock in the later period is lower than that of internal coal-rock. The higher the initial horizontal stress is, the higher the bearing capacity of coal-rock is. No matter in a higher or lower initial stress range, the incremental quantity of the later period bearing capacity of internal rock-coal is larger than that of external rock-coal. With the increase of stress transfer velocity, the peak strength of coal-rock is increased, and the effect of stress transfer velocity on the mechanical properties of internal coal-rock is more significant.

Loess has poor water stability. It will disintegrate, when encounters water, and cause instability of the building foundations in loess area. The application of lignosulfonate for loess reinforcement and related engineering properties are evaluated by experimental program including unconfined compressive strength test, disintegration test, uniaxial tension test, triaxial compression test and permeability test. The test results indicate that calcium lignosulfonate improves engineering properties of loess rather than sodium lignosulfonate. Compression and tensile strength of the stabilized soil firstly increase and then decrease as the content of calcium lignosulfonate increases. Less moisture content generates greater the density and greater strength of the solidified soil. The strength of strengthened soil increases firstly and then stabilizes as the growth of curing age. Calcium lignosulfonate presents favorable reduction on loess disintegration and penetrability. The research concludes that calcium lignosulfonate can significantly improve the engineering properties of loess. The suitable addition amount of calcium lignosulfonate should be 1.0% and the curing age should be 7 days. The scanning electron microscope analysis assists the further discussion on two mechanisms for the improvement of engineering characteristics of loess by calcium lignosulfonate: soil particles cementing and pore filling.

Based on the virtual internal bond (VIB) model, a fourth-order elastic tensor of the VIB evolution function is deduced. Two parameters in the evolution of VIB density are studied, and a numerical model of rock is developed under uniaxial compression. A general law of the influence of these two parameters on the whole stress-strain curve is obtained, and a stress-strain curve of homogeneous marble sample is simulated by the VIB model. Numerical results show that the stress-strain curve is in good agreement with experimental results. The applicability and feasibility of the VIB model for the constitutive relation of rocks are proved, which provides a new way to study the constitutive relationship.

Variable cross-section thread pile is a new type of piles applied in ground improvement. The vertical bearing characteristics of variable cross-section thread pile are studied by means of laboratory model test and numerical simulation. The difference of bearing characteristics between variable-section thread piles and ordinary straight piles and plain cylindrical piles is analyzed. And the influence of thread structural parameters and foundation soil parameters on vertical bearing capacity of variable cross-section thread pile is comparatively analyzed. The results show that the thread structure of the variable cross-section thread pile and the round-shaped pile body can greatly improve the side friction. Under the same stratum condition, the material utilization ratio (ultimate load divided by pile body volume) of the variable cross-section thread pile is about 1.3 times that of the ordinary section thread pile, and is about 3 times that of ordinary cylindrical smooth pile. Among the structural parameters of the variable cross-section thread pile, the thread width, thickness, spacing and change rate of pile section are the important factors affecting the vertical bearing capacity of single pile, and should be fully considered in the engineering design.

To solve the problems of low early strength and poor water stability of stabilized red clay, the functional components including expansion component, early strength component, thin electrical double layer structure component, waterproof component are used to improve the early strength of stabilized soil by sulphoaluminate cement. Through the single doping tests, aluminum stearate, triethanolamine, Fe(NO3)3 and gypsum are selected as the functional components of soil stabilizer., The optimal formula of functional components is further determined by orthogonal test. The unconfined compressive strength of stabilized soil can reach 8.60 MPa after curing 7 days using the optimal formula. By using XRD and SEM, the variations of mineral composition and microstructure of the stabilized soil are analyzed before and after adding functional components. The test results show that functional components used in moderation can contribute to the formation of insoluble mineral crystals with high strength and expansibility, so as to improve the early strength of stabilized soil. However, if the amount of functional components is too high, the early strength of stabilized soil decreases due to the altered connection way of stabilized soil induced by the excessive expansion of mineral crystal and the hindrance of hydrophobic membrane.

Signorini-type variational inequality has the advantage to eliminate the singularity of the infiltration point and to overcome the mesh dependency when solving the seepage free surface problem. Constraint iteration method is used in the iterative process, and the mathematical constraint is more stringent. For the free surface through the unit calculation, it is not easy to converge and even results in a shock between two kinds of solutions. On the basis of the variational inequality, the authors modify the iterative formula. The mathematical constraints are revised, and an iterative method with variable bandwidth is developed. Modifying the iterative algorithm improves the numerical stability of the variational inequality formulation of Signorini, and reduces the iteration time. After the excavation of underground powerhouse, the groundwater normally leaks from the side wall of the cavern, the determination of critical percolation point plays a key role in the analysis of leakage and the effect of drainage hole. The modified Signorini-type variational inequality is applied to simulate the seepage flow in the excavation boundary and the drainage hole of a typical project, which proves that the modified method has better convergence in the complex nonlinear three-dimensional seepage calculation.

The frozen soil wall can be simplified as the functionally graded material (FGM) thick cylinder with parabolic-distributed elastic modulus and cohesion. In consideration of the intermediate principal stress, the analytical solutions of the elastic ultimate load, the elastioplastic stress field and the plastic ultimate load are derived based on the unified strength theory. The results are further compared with that of a homogeneous model, the influence of the parameters of unified strength theory is investigated as well. The results show that the stress distribution of FGM frozen soil wall differs from that of homogeneous frozen soil wall, especially the circumferential stress changes from linear distribution to parabolic distribution. The maximum circumferential stress appears in the central thickness instead of the inner or outer wall. The elastic ultimate load is higher but the plastic limit load is lower than that of homogeneous frozen soil wall. The elastic ultimate load and the plastic ultimate load, the radial stress and the circumferential stress will increase with the increase of the parameters of unified strength theory. The conclusions can provide theoretical reference for the design of frozen soil wall.

Large-scale shaking table tests are conducted to investigate the seismic displacement relaxation zone in the reinforced slope by composite retaining structures. A new method was developed to determine the boundary line of displacement relaxation zone. The testing points corresponding to the selected allowable displacement value in displacement curves with different elevations are connected, and then a boundary line of the displacement relaxation zone is formed. It is shown that the range of the displacement relaxation zone increases with the increase of the amplitude of input seismic wave. The response of the slope displacement is gradually weakened from outside to inside of the slope under the action of composite retaining structures. The time corresponding to the peak displacement value of the slope is posterior to the time corresponding to the peak value of the input seismic wave. The slope between the relative height of 0.368 and the slope crest shows displacement coordination, and the time corresponding to the peak displacement value is close in this part but is shorter than the slope toe. The results presented in this study can be used to guide the understanding of the seismic displacement relaxation zone and the optimizing of the composite retaining structure.

Fully understanding the randomness of rock mechanical parameters and reasonably evaluating its probability distribution are the basis for the objective evaluation of rock engineering stability. About 50 specimens of each kind of igneous rock, i.e. devonite basalt and amygdaloidal basalt gained from the Baihetan Project, are used for uniaxial compression tests respectively. The stochastic distribution characteristics and the optimal probability density function form of characteristic strength, deformation parameter, characteristic strain and fracture surface angle of basalt are studied by means of statistical analysis and hypothesis test. The analysis results show that the discretization is an inherent property of basalt, and only a certain number of repeated tests can reliably assess its basic mechanical properties. The optimal probability distributions of the two kinds of basalt, including the characteristic strength, the deformation parameter, the characteristic strain and the fracture surface angle, are not the same, which are normal distribution, lognormal distribution, Weibull distribution and Weibull distribution. The statistical analysis results can not only enrich our knowledge about rock deformation and failure, but also provide experimental proof for further reliability analysis of geotechnical engineering.

To solve the large deformation problem of deep gob-side entry retaining in soft rock under high stress, lithological characteristics of surrounding rock, failure modes of supporting structure and its evolutionary process are analyzed by the methods of field investigation, theoretical analysis and similar tests. Failure mechanisms of surrounding rock and its control technology are studied systematically. The results show that the large deformation inducements of surrounding rock are weak thick mudstone with softening property and water absorption behavior, as well as its fragmentation, dilatancy and long-term creep in strong disturbance and highly centralized stress state. The cross-section shape of roadway after deformation and failure of surrounding rock is obviously asymmetric in both horizontal and vertical directions. As the original supporting system of surrounding rock does not form into a complete bearing structure, each part of the supporting system is destroyed one by one. The failure sequences of surrounding rock are as following: (1) roof fracture of backfilling area, (2) backfill fracture under eccentric load, (3) rapid subsidence of roadway roof, (4) external crack drum and rib spalling of solid coal side, and as a result, the instability of the whole surrounding rock occurs. The partitioned coupling support and the quaternity control technology of surrounding rock are proposed, which take the roof of backfilling area as a key link. The technology can improve the overall stability of gob-side entry retaining, avoid support structure instability caused by local failure of surrounding rock, and ensure the safety and smoothness of roadway.

The high pressure and water-bearing caverns close to the face of karst tunnels are liable to induce geological hazard of water inrush and mud outburst, therefore, the determination of appropriate rock wall thickness is a pivotal problem which needs to be solved immediately in tunnel construction. Two procedures, one with linear Mohr-Coulomb criterion and the other for the case of nonlinear Hoek-Brown failure criterion are proposed to compute the rock wall thickness based on upper bound theorem of limit analysis theory. According to the three-dimensional failure pattern established here, the specific procedures are deduced to derive the expressions of rock wall thickness with these two methods. The linear Mohr-Coulomb method is adopted to calculate the rock wall thickness under the surrounding rock ranging from levelⅠto Ⅴ. The results indicate that with the decrease of surrounding rock level, namely a lower values of cohesion and internal frictional angle, the thickness increases continuously. As to the nonlinear Hoek-Brown approach, the effect of each parameter on rock wall thickness is analyzed, and the failure shape and scope of rock wall are plotted based on the calculation results. Meanwhile，the suggested values of constant A, B in Hoek-Brown criterion are given. Namely, the surrounding rock changes from the level Ⅰ to Ⅵ, the lithologic condition ranging from good to bad，it is suggested to give A for 0.5~0.3 and B for 0.7~0.9. The rock wall thicknesses of Yunwushan tunnel and Yesanguan tunnel are calculated with two methods, respectively, and the results are in good agreement with engineering practice, which verifies the validity of the methods in this literature. The two methods could provide reference for the design and construction of tunnels in high-risk karst regions.

Based on the field model tests of tunnel-type anchorage in the Pulite bridge, the deformation and failure process of rocks surrounding tunnel-type anchorage are revealed via numerical simulation. The failure surfaces in the surrounding rocks initiate around the rear interfaces between the plugs and rocks, and propagate outward with a frustum shape. The failure mode is tensile-shear. Moreover, the rocks near the free surfaces in the front of the plugs are pushed outward and damage with tensile mode. The stresses vary complicatedly as the pullout force increases. Based on these, a computational mode of the pullout force for the surrounding rocks is proposed by establishing the equilibrium relationship of forces acting on the failure surfaces. Different from the published literatures, this mode embodies the “clamping effect”, and reveals the complicated variation of forces on the failure surfaces as well. It is necessary to execute field tests and numerical simulations in order to assess the values of the forces on the failure surfaces. In future, the possible shapes of the failure surfaces and the variation ranges of forces on the failure surfaces can be suggested after the accumulated studies for various rocks with different strengths and structures. The computational mode is verified by the testing results, and is used to estimate the pullout force of the prototype anchorage. The results show that the ultimate pullout capacity is very large. The design philosophy of the tunnel-type anchorages is considerably conservative nowadays. We believe that it is probable to apply the tunnel-type anchorages in moderate-strength and even soft rocks. The issues concerning the changes of failure surfaces in different rocks, the influence of rock structures on the pullout capacity, etc., are discussed.

In this study, we studied the surface subsidence law and the shortcomings of predicting surface subsidence by Knothe time function model under loose formation conditions. To express the loose formation subsidence, a time impact factor c2 is introduced into the original time, and a two-factor time function model is developed. Theoretical analysis results indicate that although the two-factor time function has characteristics of slow convergence and strong adaptability to parameter change, it is not complete in accordance with the dynamic process of the surface subsidence. Hence, we improve the two-factor time function，and then verify the applicability of improved two-factor time function for three different thickness (i.e., thin, thick and extremely thick) of loose strata. The results show that the improved function can predict the whole dynamic process of ground point subsidence under the conditions of different thickness of loose strata. The results performed in the study can provide reference for coal mining under building, railway and water body.

The stability of surrounding rock support structure is the key to the design of underground structure. To overcome the insufficiency of statistical information on surrounding rock parameters of deep tunnels, the information-gap theory is introduced to develop a non-probabilistic reliability analysis method for surrounding rock. The info-gap model of dimensionless parameters is given based on the uncertainty level, and the robust function of reliability analysis is obtained according to the system model and performance requirements. The maximum fluctuation amplitude of uncertainty parameter which can be tolerated before structural failure is taken as a robust reliability index. An optimal support resistance of homogeneous elastoplastic surrounding rock is obtained based on the slip-line field theory. Then a response function of stability analysis of surrounding rock support structure is established. The engineering example illustrates the specific operation procedures of robust reliability analysis. The parameter analysis shows that the greater the support resistance is, the more stable the structure is. In the meanwhile, it is shown that increasing the internal friction angle and cohesion of the surrounding rock is the key to improve the stability of the support structure. The proposed procedure is a reasonable and effective method to deal with the uncertain problem when the parameter information and sample data are limited.

The deformation mechanism of the foundation pit is not consistent with the real in-situ deformation in traditional method for stability analysis. The surface settlement curve caused by foundation pit excavation in soft soil area enables the establishment of the admissible velocity field and deformation mechanism for basal stability problems in excavations. The soil inside the deformation mechanism acts as a continuous deformation body without apparent failure surface at the boundary. A new method for the stability analysis of foundation pit is developed based on upper bound method. The deformation mechanism adopted in the method is more suitable for the foundation pit deformation, considering the influence of the depth of supporting structure on the uplift deformation of foundation pit. The upper bound method based on Terzaghi mechanism and Prandtl mechanism is compared with the multi-block upper bound method in engineering examples to verify its rationality and applicability.

The force distribution coefficient is introduced according to the principle of the stiffness distribution; a method of calculating the horizontal stiffness coefficient of the ring support system is developed, and its analytical solutions are derived; furthermore, the revised analytical solutions are given. The procedure is employed to calculate the horizontal stiffness coefficient of the ring support system of an extra deep foundation pit with ring support. The influence of different closed ring beams and transmitting beams on the horizontal stiffness is also analyzed. The calculated results by proposed procedure are compared with those by three-dimensional finite element method. The results show that the error with the two methods is small, and the horizontal stiffness of the ring support system is mainly determined by the closed beam of the force bar, and is trivially affected by the force beam of the transmitting beam. According to the proposed analytical formula, the result is accurate and simple, which can provide the basis for determining the design values of the horizontal stiffness coefficient of the foundation ring support system.

The seismic response analysis of local complex sites with nonlinear characteristics has been the key problem to solve in prediction of seismic motion. Frequency domain equivalent linearization, widely used in the seismic response analysis of one-dimensional stratified sites, is extended to time domain and two-dimensional problems. A time-domain explicit finite element method can be used to consider nonlinear characteristics and it is suitable for seismic response analysis of complex engineering sites. In this method, the inner domain of the method is mainly used to realize the low-order finite element scheme of the explicit algorithm. The boundary of the artificial boundary is simulated by the boundary of the transmission boundary. The maximum tangent strain in the one-dimensional model is replaced by the maximum tangent strain in the plane strain state, and the equivalent shear strain is obtained according to the tangent strain of the whole time process. Each time the whole solution is solved by the time domain center difference, and the nonlinear characteristic analysis is done by iteration. In order to verify this method, two typical site models of horizontal stratified and two-dimensional basins are selected for simulation analysis. The results are compared with solutions of the traditional one-dimensional equivalent linearization model and the two-dimensional differential nonlinear calculation. The results show that the solution is in good agreement with the reference solution, and prove the reliability of the method. This method is used to simulate the surface vibration of the US Turkey Flat test site. The results are compared with one-dimensional equivalent linearization model and the measured record. The reliability of the method and the difference with the existing analysis model are discussed, and the influence of the nonlinear characteristics on the seismic motion is illustrated.

Due to excess pore pressure and other factors of deep soft soil, the effect of adjusting the shield parameters on the soil displacement tends to have a certain delay. The adjustment of construction parameter in current session influences more on the soil displacement in later session rather than current. Two same monitoring sections are set up to survey the soil displacement from the shield tunnel in Shanghai soft soil. The effect of each parameter adjustment to the displacement disturbance is analyzed by changing the key shield parameters in different stages during construction. Chamber pressure is adjusted before the shield cutter reaching the monitoring section. Advancing speed is adjusted while shield cutter crosses the monitoring section. Grouting quantity is adjusted when shield tail reaching the monitoring section. Through the monitoring data and the time-effect analysis of the correlation coefficient, it is found that the soil displacement is affected by the disturbances of the pre-adjusted soil pressure when the shield crosses the cross-section, and the soil displacement at the shield tail reflects the squeezing effect caused by advance rate, while the displacement of soil at the late consolidation stage shows the stabilizing effect caused by the increase of the grouting amount when the shield tail prolapse. Therefore, it is not only necessary to deal with the current soil deformation, but also to pay attention to the deformation and prediction of the soil after the adjustment of the parameters so as to avoid the occurrence of accidents due to the delay effect in soft soil.

For the integration of GIS spatial information and a variety of field data obtained by numerical simulation, FEM (finite element method) is necessary to be combined with GIS. To improve the efficiency of system development, the open source softwares, such as GRASS GIS and VTK, are used to establish complex system development framework combining FE simulation and GIS by Python language. The platform named 3DPyGisTFEM enables seamless coupling between FE calculation and 3DGIS for tunneling analysis. Moreover, the algorithm of tunnel model generation connects a series of contour lines with tunnel center lines. The geological sections of tunnel excavation can be obtained by cutting operation on different strata layer DEMs and tunnel models. The triangular meshes for finite element simulation introduced by Delaunay mesh generation algorithm improve TIN model of GIS. The field data of research area are generated by interpolation of multiple geological sections simulation results from FEM. Then, the seamless coupling method with FEM in GIS is realized through comprehensive analysis of field data using GIS spatial analysis methods. The Huangjiazhai tunnel engineering example shows that the ground surface elevation from tunnel crown has greater influence on surface settlement than other factors, such as relative slope, buffer and etc.

At present the limit equilibrium method is generally used to evaluate the stability of composite foundation. In this procedure, the composite foundation theory assumes the cohesion and friction angle of rigid pile are equivalent to that of the whole foundation, and then the safety factor of the whole foundation is obtained by circular slice method. This theory considers the shear failure at critical state for all rigid pile and the soil. However, according to the relevant research results, shear failure is not exclusive for group piles, and the safety factor based on the shear failure mode may tend to be overestimated. Based on the actual failure mode of rigid pile group, a strength reduction method is developed for rigid pile failure. That is, when the critical state of composite foundation system is searched by strength reduction method, the failure mode of rigid pile should meet the actual damage. At the same time, on the basis of the deformation and failure characteristics of the rigid pile, methods for identifying critical state are discussed. The feasibility and validity of the proposed method are verified through comparing the proposed method and the traditional method only considering shear failure.

Every single particle is simulated by a polygon discrete element to capture the realistic shape of rockfill materials. A polygon discrete element method (PDEM) is developed by adopting a simple contact detection program and a polygon/polygon contact model. A linear program is adopted to detect the contact details between polygons. Then the normal contact force is calculated by a potential energy based polygon/polygon normal contact model, and a polygon discrete element calculation method is formed. Based on this method, a program called PDEM is developed to study the interaction between particles and both the translational and rotational motion of every particle from the microscopic view. The effect of micro-properties (e.g. particle shape, size, material properties et al.) on the macro-strength and deformation is enabled. A two-dimensional model test of a coarse aggregate was carried out by PDEM program. The stress and deformation laws consistent with the lab experiment were obtained, and the method and procedure were used to study the effectiveness of the rockfill.

The mechanical properties of lunar soil simulant which is used as the bed material of the model test for the lunar exploration, directly affect the design of structures like lunar probe and lander, and the shear strength is one of the main mechanical properties. To determine the mechanical properties of TJ-1 lunar soil simulant used in soft-landing model tests, a series of triaxial tests with triaxial apparatus under standard stress path is carried out to obtain its stress-strain relationship curves for different relative densities, shear rates and confining pressures. The result shows that, TJ-1 lunar soil simulant possesses the characteristics of strain softening and an apparent cohesive force of certain values, the peak inner frictional angle lies in the range of 43°-51°. With the increase of relative density of lunar soil simulant, the characteristics of strain softening grows more obvious and the values of cohesive force and angle of internal friction become greater; meanwhile, the values of shear strength indices decrease generally when the loading rates becomes faster. A numerical model of triaxial test using PFC3D is established to study the effect of meso parameters, such as inter-particle frictional coefficient, initial porosity and particle stiffness on the shear strength indices of lunar soil simulant. The simulation turns out that the inter-particle frictional coefficient is the primary factor affecting the angle of internal friction, while the other two have less effect. Within a certain limit value, the inter-particle frictional coefficient increases approximately linearly with the angle of internal friction.

Discontinuous deformation analysis (DDA) method benefit greatly in discontinuous deformation problems, whereas contact disposing and open-close iteration used in DDA cost significant amount of time. In order to improve the computational efficiency of the contact searching in the DDA method and maintain high accuracy, an improved contact searching algorithm is developed by changing the contact searching mode within the distance criterion. By increasing the pre-judgment, the number of corner points that need to be determined are reduced before contact searching. Two types of angular-edge contacts are distinguished and the search of these two angular-edge contacts is assigned to different loops, which changes the contact searching logic under the distance criterion. Two computational models verify the accuracy and efficiency of the improved program. Model 1 is used to test the program under various contact conditions with improved accuracy. Model 2 is employed to calculate the Donghekou landslide with improved efficiency of about 10% under the premise of guaranteeing the accuracy of the calculation results.

Brillouin optical time domain reflectometer/analysis (BOTDR/A) is one kind of important distributed optical fiber sensing technology. Using the BOTDR/A-based distributed optical fiber technology to detect deformation of pile foundation, the vast amounts of detection data need smoothing and denoising. The paper introduces most frequently used embedded techniques of the sensing optical fiber, the characteristics of detection data, the role of massive data smoothing and denoising on the detection data handle and analysis. We developed the concept and proposed the implementation process of the feature point compression algorithm (a new smoothing and denoising method). Based on data measured from practical engineering, the smoothing and denoising effect of the method is analyzed, and its applicability is also verified. The results show that the proposed method is simple and efficient in processing the data from pile foundation detection, compared with the conventional algorithm, it can smooth and denoise data without losing the characteristics trend of detected data, and can achieve satisfactory results as expected. It can be applied to the distributed data processing of optical fiber pile foundation detection.

A self-developed servo-controlled rock triaxial test system with dynamic disturbance is introduced in detail. The test system can apply dynamic disturbance in the process of conventional triaxial compression. The test system consists of four parts: axial loading subsystem, confining pressure subsystem, dynamic disturbance loading subsystem and data collection subsystem. The maximum axial load and confining pressure of the test system can be 2 000 kN and 70 MPa, and the maximum dynamic disturbance load of the system can be 300 kN and the highest frequency of the dynamic disturbance load is 70 Hz. A set of experiments about dynamic disturbance in uniaxial compression is performed on marble with the developed test system. The experimental results indicate that: when the amplitudes of the dynamic disturbance are in the same frequency, the larger the amplitude of disturbance is, the shorter time is the disturbance to the rock failure, vice versa. It can be seen from the failure modes after experiments that the marble samples are fragmentized under the dynamic disturbance load. The lower the amplitude of the dynamic disturbance load is, the higher degree of fragmentation is. The servo-controlled rock triaxial test system is stable and reliable, thus it is worth generalizing the use of the testing system in other laboratories to explore mechanical properties of deep rocks.