Using the self-developed soil tensile strength tester, the tensile strength variations of the remolded granite residual soil with water content in wetting or drying process were studied. The microscopic mechanism of the tensile strength variation was investigated through the theories of cementation force and absorbed suction. The results show that the tensile strength first increases and then decreases with increasing the water content, and the relationships between tensile strength and water content on both sides of the peak value can be expressed by exponential functions. In the process of humidification, the tensile strength first increases and then decreases with the increase of moisture content, and the data on both sides of the peak are fitted by linear functions. In the drying process, three stages can be identified in the tensile strength, i.e. exponential increase stage, stable stage and slight decrease stage, the peak tensile strength is 4 times of tensile strengths at different moisture contents. The change of tensile strength of granite residual soil in the process of humidification with different water contents are mainly controlled by absorbed suction. While the change of tensile strength in the drying process is controlled by both absorbed suction and cementation force, the contribution of the cementation force to the tensile strength is more than 70%. The dry cracking process of soil corresponds to several stages of the tensile strength change in the drying process. In the drying process, absorbed suction is the source of the internal tensile stress of soil, indicating that absorbed suction is not only a contributor to tensile strength, but also a destroyer of tensile strength. The results of this study explain the formation source of the tensile strength of the soil and the main controlling factors of its change from another perspective.

In order to investigate the energy evolution and failure characteristics of single fissure carbonaceous shale under drying-wetting cycles, intact and fissure carbonaceous shale samples with fissure angles of 30°, 45°and 60° were fabricated respectively. MTS815 rock mechanical test system was used to conduct triaxial compression tests under different drying-wetting cycles. The influence of drying-wetting cycles on the strength, failure mode and energy evolution of single fissure carbonaceous shale were studied. The results show that the elastic energy and dissipated energy at crack initiation stress, damage stress and peak stress present exponential relationships with drying-wetting cycles. The elastic energy and dissipated energy at crack initiation stress and dissipated energy at damage stress are less sensitive to drying-wetting cycle, while the sensitivities of elastic energy at damage stress, and elastic energy and dissipated energy at peak stress are relatively high. The failure mode of carbonaceous shale is dominated by drying-wetting cycle and fissure angle, in which the drying-wetting cycle is the main controlling factor, and the fissure angle is the secondary controlling factor. It is found that tensile shear failure occurs in dry rock sample with fissure angle of 30°, while the dry rock sample with fissure angle of 45°and 60° are subjected to shear failure. With the increase of the number of drying-wetting cycles, the macroscopic length of the main crack increases, the density of secondary cracks increases, and the failure mode transforms to shear-tension composite failure. With the increase of the number of drying-wetting cycles, the energy storage level at crack initiation stress K_ci and the energy storage level at damage stress K_cd increase gradually. The higher the energy storage level at crack initiation and damage stress is, the more likely the crack initiation and rock damage occur. K_cd can be used as an warning indicator of rock failure. A larger K_cd indicates that the rock is more vulnerable to failure.

Shrinkage is inherent to expansive soil, usually resulting in slope and foundation cracking, but there is little understanding about the influence of structure on shrinkage characteristics. Using an automatic shrinkage test device, comparison tests on shrinkage and scanning electron microscope (SEM) tests for undisturbed and remolded expansive soil were carried out under the same humidity and constant temperature. The results show that compared with undisturbed soil, remolded soil has smaller evaporation rate in the water flow stage, slower shrinkage stability rate in the vapor evaporation stage and larger volume shrinkage strain in the end. For the remolded soil, the linear section of the curve of volume shrinkage versus water content is longer, the slope larger, and the transition between the linear section and the stable section not obvious, while the undisturbed soil is on the contrary. The soil shrinkage characteristic curves (SSC) of remolded and undisturbed soil basically coincide in the section at higher water content; with the decrease of water content, the SSC of remolded soil decreases faster and the corresponding water content range is wider, and when entering the residual-zero shrinkage stage, the void ratio is obviously smaller. Chertkov shrinkage model is suitable for undisturbed expansive soil, but not for remolded one. SEM test results show that the undisturbed expansive soil has stronger primary structure than remolded expansive soil. Under the same initial density and humidity, there exists obvious differences in microstructure, such as particle arrangement, contact mode, cementation state, pore size and distribution characteristics between the undisturbed and remolded expansive soil, resulting in smaller water migration rate and larger matrix suction of remolded soil during evaporation, which is the internal reason why remolded soil shrinks more violently than undisturbed soil. The research results can provide a reference basis for the design of slope engineering protection for expansive soil slopes.

Calcareous sand is a natural foundation material for ports, airports and some civil buildings in ocean areas. Through the one-dimensional compression creep test of calcareous sand and the analysis of its micro-structure, it was found that the surface pore area decreased after creep and showed a dispersed distribution. In addition, the characteristics of instantaneous deformation, rapid deformation and attenuation deformation of the sample during the test were highly correlated with the particle size. The relative particle breakage rate and mass fractal dimension improved based on fractal theory were used to describe the degree of particle breakage after creep. The relationship between the decay of fractal dimension and creep with time, as well as the linear relationship between the fractal dimension of macroscopic mass and the fractal dimension of microscopic surface was obtained. On this basis, the fractal fracture behavior of calcareous sand with a single particle size group during long-term creep was analyzed at multiple scales, and the corresponding macro and micro cross-scale correlation was studied. The development of particle breakage and the variation of microscopic pores during creep were obtained. This study proved the rearrangement, crushing and grinding behavior of calcareous sand particles in the creep process, and revealed the creep mechanism of calcareous sand.

Based on the engineering background that rock masses of underground reservoirs in mines are frequently disturbed by cyclic loads such as mine earthquake and mining stress, uniaxial compression and cyclic loading tests for sandstones with different water contents were carried out in laboratory. The crack propagation and failure laws of sandstones with different water contents were revealed by digital speckle technique. Based on SEM micro analysis, the micro deterioration mechanism of sandstones with different water contents under cyclic loading was obtained. The test results show that the peak strength of sandstone decreases gradually with the increase of water content under both uniaxial compression and cyclic loading conditions. The peak axial strain variation of dry sandstone experiences four stages of initial deformation, constant velocity deformation, accelerated deformation, and instability failure, and that of the water bearing sandstone experiences three stages of initial deformation, constant velocity deformation, and instability failure. With the increase of water content, the peak axial strain in the corresponding stage gradually decreases. It is verified by the deformation rate analysis method that water has no effect on the deformation memory characteristics of sandstone. Under uniaxial cyclic loading condition, the failure mode of sandstone gradually transits from tension–splitting failure at dryness to tension–shear mixed failure, and presents a single shear failure at saturation. SEM results show that with the increase of water content, the fracture structure plane gradually transits from smooth structure, round structure, and sheet structure to completely broken structure. With the increase of water content, the absolute damage parameter increases, which reflects the positive correlation of water–rock coupling damage, and the cumulative damage parameter larger at the same cycle accumulates faster.

The difference of gas production law between initial stage and later stage of shale gas well is essentially attributed to the difference of occurrence, migration and production mechanisms of adsorbed gas and porous medium-confined gas in three dimensional stress states. In order to reveal the influence of average effective stress on the production law of porous medium-confined gas in the initial stage and adsorbed gas in the later stage of coal shale gas well production from a micro perspective, and to simulate the whole processes of coal shale gas adsorption and desorption in situ stress state, nuclear magnetic resonance T₂ spectrums method was applied to the whole process of experimental research on isothermal adsorption and desorption of the same coal shale sample situ stress state from Dongbaowei Mine #36 seam in Shuangyashan basin. The average effective stress was taken as the comprehensive measurement index of coal shale, and the amplitude integral of nuclear magnetic resonance T₂ spectrum was used as the characterization index of micro adsorbed gas and porous medium-confined gas. The relationships between micro adsorbed and porous medium-confined gas content and average effective stress of coal shale in adsorption and desorption were quantitatively studied. The relationships between the hysteresis coefficient of micro adsorbed and porous medium-confined gas and the average effective stress were studied quantitatively. The influence of average effective stress on the occurrence and output of micro adsorbed and porous medium-confined gas in coal shale was clarified by multi factor linear regression. The experimental results showed that, the adsorbed gas content of coal shale and average effective stress could be fitted by Dubinin-Radushkevich function model in the adsorption and they could be fitted by Weibull function model in the desorption. The porous medium-confined gas content of coal shale and average effective stress could be fitted by linear function model. The hysteresis coefficient of micro adsorbed gas and the average effective stress accorded with the logarithmic function model. However, the decrease of average effective stress had little effect on the hysteresis coefficient of micro free gas, and the hysteresis coefficient of porous medium-confined gas was approximately 41.53%. The pore pressure of reservoir and vertical stress of overlying strata were the main control stress factors of micro adsorption and desorption, respectively. The occurrence and output of free gas were mainly related to the stress of surrounding rock.

To study the long-term deformation after construction of high-filled soil under partial saturation, the rate sensitivity and creep tests of unsaturated compacted soil under controllable matric suction were carried out respectively, and the time-dependent corresponding relationship between them was analyzed. The rate-sensitivity tests used the triaxial shear method at different loading rates to analyze the effects of matric suction (0, 100, 200, and 300 kPa), loading rate (0.4 and 0.02 mm/min), and over-consolidation ratio (1, 4, and 8) on the strength and deformation characteristics of the soil. The 0.45, 0.65, and 0.85 times of shear strength are determined to be the third-order stress level loads of triaxial shear creep respectively. The triaxial shear creep tests of unsaturated compacted soil were carried out under four controllable matric suction forces (0, 100, 200, and 300 kPa), referring to the Chen loading method, and under three stress level graded loading. The results show that: 1) The rate sensitivity parameter ρ  of unsaturated compacted soil decreases with the increase of matrix suction, and its rate sensitivity also decreases. 2) With the increasing of matric suction, the initial maximum creep rate, stable creep rate and creep deformation of unsaturated compacted soil decrease significantly. 3) The strain rate-strain relationship line determined by the creep test is consistent with the strain rate-strain data points obtained by the rate sensitivity test, which proves that there is a certain time-dependent corresponding relationship between the rate sensitivity and creep, and this relationship becomes more significant with the increase of matrix suction. 

With the development of urban city scale, more and more refuse soil land is used to conduct engineering construction. Since the refuse soil has the characteristics of high compressibility, biodegradability, and fiber reinforcement, geotechnical engineering such as the cone penetration test, pressure-meter tests, static pile, etc., will meet new challenges in this kind of site. Based on the modified Cam-clay model with fibrous reinforce considered and large deformation theory, through introducing an auxiliary variable, the cavity expansion issue is transformed to solve a set of first-order differential equations with given boundary conditions. The modified Cam-clay model is used to verify the accuracy of this research. Then the effect of over consolidation ration and fiber content to the solution is studied systemically. The results show that the refuse soil has a larger plastic radius compared with clay soil. With the increase of over consolidation ratio and fiber content, the inter cavity pressure and plastic radius show an increasing and decreasing tendency, respectively. After elastic and plastic stage, the refuse soil element with different fiber content reaches nearby the critical state of the paste component.

Rigid sliding blocks are used to construct two failure modes of the tunnel's circumferential excavation surface of circular tunnel. The compiled nonlinear programming program is used to solve the optimal upper bound solution of the support force coefficient σ_T /c (σ_T is uniformly distributed support load and c is the effective cohesion) and the stratum failure mode so as to reveal the influences of stratum parameters on tunnel stability. A simple and practical simplified formula for the ultimate support force of the tunnel's circumferential excavation surface is proposed. For undrained condition, the failure region is mainly concentrated in the upper part of the tunnel when the tunnel depth ratio H/D (H is the buried depth and D is the tunnel diameter) and the gravity coefficient γD/c (γ is unit weight) are small. With the increase of H/D and γD/c, the starting position of the slip line gradually expands to the bottom of the tunnel along the tunnel contour, and the failure region expands to the horizontal direction. For drainage conditions, there are three main stratum failure modes. When the internal friction angle ϕ and γD/c are large, with the decrease of the dilatancy coefficient, the ultimate supporting force increases significantly, and the range of failure region varies greatly, which may even cause a change in the failure mode. The ultimate supporting force of the tunnel circumferential excavation surface can be quickly obtained through the proposed simplified formulas.

The traditional SWCC test method is time-consuming, and it is of great practical significance to develop a method that can quickly determine the SWCC of unsaturated soil. In order to predict the SWCC of compacted loess rapidly, the water potential and moisture content of compacted loess with different dry densities were tested, and the pore size distribution curve was measured using nuclear magnetic resonance (NMR) technology. Based on the test results, a rapid prediction method of the soil-water characteristic curve of Yan’an compacted loess was established based on the void ratio, and its accuracy was verified by the measured data. The results show that the fractal dimension D in the prediction model can be determined by the cumulative pore volume of two points (peak point and half-width point) on the pore size distribution curve and the slope of the pore size in a double logarithmic coordinate; and it can be expressed by the void ratio based on the linear relationship between void ratio and dominant pore diameter in logarithmic coordinates. The inlet value of SWCC is controlled by the diameter of macropore; the slope of the transition section is controlled by the volume of mesopore. There is a critical pore size in compacted loess, the residual water content is mainly controlled by the pore volume whose pore size is smaller than the critical pore size, and an empirical method is proposed to calculate the residual volume water content. Compared with traditional methods, the proposed method can save a lot of time in determining SWCC.

The binary medium model has been widely studied in unfrozen geomaterials, however, it is still not well studied for frozen soil. In order to investigate the strength-deformation characteristics of frozen silty sand in triaxial test, the binary medium theory is introduced to interpret the stress-strain relationship of frozen soil. There are plenty of parameters for existing binary medium model, and the determination of parameters is with complexity. A binary medium model is proposed based on simplified breakage parameter. The triaxial tests of frozen soil were performed under five kinds of fine particle content and four kinds of confining pressure conditions, and the validity of proposed model was examined by test results. It is revealed that the stress-strain relationship can be divided into three stages with the increase of axial strain, namely, linear elasticity stage, elastoplastic stage, and strain softening stage. Based on binary medium model, all three stages can be well explained by the transformation theory of bonding element and friction element. Under the identical confining pressure conditions, both deviatoric stress and the maximum values of bulk expansion decrease, while the shear strength decreases linearly with the increase of fine particle content. Considering cross-section area correction, the silty sand with different fine particle contents presents softening characteristics, and the volume deformation shows the pattern from shrinkage to expansion with the increase of axial strain. The turning points of the three stages of deviatoric stress development are in good agreement with the extreme point of volume shrinkage and the turning point of volume expansion. Comparing the measured deviatoric stress in triaxial tests with the calculated by binary medium based on simplified breakage parameter, it is believed that the proposed model is able to simulate the stress-strain relationship of frozen silty sand in triaxial tests.

Due to the severe disturbance between closely spaced tunnels, the rock pillar is in the unfavorable state of single or double-direction compression, and the construction safety is seriously affected. Therefore, the prestressed and grouted pillar-reinforcing bolt is widely used to support the rock pillar actively. The mechanical models and analytical methods are established to clarify the function modes and control mechanism of the pillar-reinforcing bolt. The theoretical approach is verified by field test, the influencing parameters are analyzed, and the corresponding engineering applications are carried out. The results show that the pillar-reinforcing bolt can provide strong horizontal restraint on the rock pillar, improve the mechanical properties of the rock mass, and has the extrusion reinforcement effect. The pillar-reinforcing bolt also utilizes friction resistance to improve the stress state of the shallow surrounding rock and anchor the deep rock, which has the load transfer effect. The axial force and shear stress of the pillar-reinforcing bolt decrease nonlinearly from both outsides to the insides, and the function range is limited within the shallow layer of the rock pillar. This trend is verified by field measured data. The parameter influences on the mechanical behavior of the pillar-reinforcing bolt are systematically analyzed, and the critical bolt length and reasonable bolt diameter are proposed accordingly. Based on the engineering practice of the closely spaced tunnels in the Great Wall Station of Beijing Zhangjiakou high-speed railway, the design of pillar-reinforcing bolt is actively enhanced. After the design change, the average values of surrounding rock pressure, crown settlement, and horizontal convergence are reduced by 12.2%, 14.1%, and 10.2%, respectively. The safety state of closely spaced tunnels is significantly safeguarded.

In TBM excavation, the composite rock strata are often encountered, in such a case, it is not easy to estimate surrounding rock strength during tunneling where the tunnel face and wall tend to collapse. For improvement of tunneling efficiency and disaster prevention, it is necessary to estimate surrounding rock strength in real time. Based on laboratory tests and field data in the construction of Chongqing Railway Line 9, it was found that the thrust F_N is proportional to rock strength, it was also found that the ratio of the torque force to thrust, T/F_N were proportional to p^0.5 (penetration p). In this study, for composite rock strata(including sandy mudstone, sandstone and limestone) surrounding tunnel, a method that can quickly estimate surrounding rock strength from thrust and torque measured in-site, was developed. The method can estimate rock strength in real time with two constants α₁, α₂ which can be obtained by linear fitting of the field data for TBM. The method had been already applied to more than ten tunnels. It was found that two constants were only related to the number of disc cutters n and cutter-head diameter d for this geological environment of composite rock strata. The results provide a more practical and feasible idea to estimate surrounding rock strength in real time, and also can improve the reliability and safety of tunnel TBM construction.

For the karst tunnel with pipeline cavity in the surrounding rock, it is very easy to accumulate high water pressure in the pipeline cavity due to the influences of heavy rainfall on the surface and groundwater, which will lead to lining cracking, water leakage and water gushing diseases. To explore the influence of high water pressure on the lining structure, a model test of pipeline karst tunnels under high water pressure was carried out, and the internal force characteristics of tunnel lining under the influence of cavity position and head height were studied. Based on this, the numerical calculation model of extended working conditions was established. The effects of cavity diameter, cavity position and water head height on the lining structure were further explored. The results show that the inner side of the lining in contact with the cavities bears larger positive bending moment, when there are karst cavities around the tunnel, which are the most unfavorable stress positions of the lining. The internal force of the lining increases greatly, with the increase of cavity diameter and water head height in the cavity. The location of the cavity affects the internal force distribution of the lining, and the anti-water pressure capacity of the lining is the smallest, when the cavity is located at the tunnel vault. The research results can provide reference for the structural design and safe construction of pipeline karst tunnels.

The construction of Guangdong-Hong Kong-Macao Greater Bay Area is a major national development strategy of China. Shenzhen is a core city in the Greater Bay area. The karst in Shenzhen typically is found in Longgang and Pingshan districts. It has brought great challenges and threats to the underground exploitation and ground construction safety for the city. In this paper, borehole data are first collected from karst geotechnical investigation projects in Shenzhen and from the relevant literature. Based on the data, the spatial features of the karst in Shenzhen are statistically characterized considering strata and rock type, rock stratum depth and burial type, main corrosive indices of the groundwater, depth of the karst caves, thickness of the cave ceiling, cave height, fillings, karst line ratio, karst borehole ratio, and ground karst growth density. Results showed that the karst in Shenzhen is typically buried shallowly, but largely varies as of the spatial features. Statistically, on average the karst cave is about 20 m in depth, 2.5 m to   4 m in height, and mainly half filled with silty clays. On average the karst is about 15% for line ratio, 40% for borehole ratio, and over 300 caves per km² for the ground karst growth density. Overall, over 90% of the sites are ranked as high in karst development. It is also found that the above karst parameters follow lognormal as well as Weibull distributions. The ceiling thickness tends to be smaller as the rock depth increases for limestone stratum, whereas these two factors are statistically uncorrelated at a significance level of 0.05 for marble stratum. The cave height appears to be statistically independent or positively weakly correlated to rock depth, ceiling thickness, underground corrosive indices, and groundwater table. The findings from this paper provide valuable priori information to risk assessment on karst hazards in Shenzhen. 

In order to solve the problems of the obvious dynamic pressure, roof cutting subsidence and large deformation of the gob-side entry retaining in soft and thick coal seam fully-mechanized top-coal caving mining. The dynamic pressure characteristics and deformation mechanism of gob-side entry retaining are clarified, through field investigation, theoretical analysis and numerical simulation. A deformation coordinated support system of gob-side entry retaining arranged along the roof of soft and thick coal seam is proposed. The results show that the mining thickness of fully-mechanized top-coal caving mining is large, when retaining the gob-side entry along the coal seam floor, the bearing capacity of the coal roof is poor and the bearing capacity between the floor, gob-side entry filling body and roof support system is uncoordinated, which are the main reasons for the obvious dynamic pressure and large deformation of the gob-side entry retaining in the soft and thick coal seam. The proposal of the deformation coordinated support system in gob-side entry retaining along coal seam roof improves the coordinated bearing capacity of the coal wall, roof, floor and gob-side entry filling body, which can effectively ensure the stability of surrounding rock in the soft and thick coal seam gob-side entry retaining. The successful application of the research results to Gu-cheng Coal Mine proves the feasibility of the support system in soft and thick coal seam fully-mechanized coal caving mining gob-side entry retaining.

For the checking of bearing capacity of foundation under eccentric loading, the method given by Meyerhof is first introduced，and validated for its accuracy through comparison with calculations by using the finite element upper and lower bound limit analysis method which can compute general limit loads accurately. The foundation soil considered can be either general c- soil under drained conditions or undrained cohesive soil with its undrained strength increasing linearly along depth. In particular, the influence of the footing embedment depth on the calculation accuracy is discussed according to the understanding of relevant mechanism，and the largest eccentricity below which the bearing capacity due to footing embedment depth can be taken fully into account is clarified. Thereafter, the checking method proposed in the Chinese design code is compared with the Meyerhof method through calculations by using the improved bearing capacity formulae given by the authors, which indicates that the latter method is more reasonable.

To study the law of surface displacement during pipe roof construction of pipe-jacking group, this paper analyses surface displacement data based on the Tianlin Road passing under Middle Ring Road Tunnel Project in Shanghai. Measured data shows that deformation development during the pipe roof construction can be divided into seven stages: 4 construction stages and 3 suspending construction stages. The surface displacement during the pipe roof construction comprises ground loss settlement and ground heave caused by grouting. In the suspension stages, the surface displacement is consolidation settlement. In this paper, the surface displacement is described by the Peck equation. The width coefficient i of surface settlement trough and the ground loss ratio η were back analyzed from the field measured data. Based on the analysis results, the calculation formulas of i and η were proposed for Shanghai soft clay. i is related with the pipe radius R, pipe buried depth h and internal friction angle of soil φ, and the formula of η is described by a hyperbolic function of time after jacking. The surface heave caused by the grouting can be separated to the negative ground loss caused by each pipe jacking with grouting. The above method was used to predict the surface displacement and the predicted results were compared with measured data to verify the correctness of the method in this paper, which can provide scientific reference for the prediction of surface displacement caused by similar pipe roof method construction.  

A super large centrifuge foundation was buried in the soft soil. the vibration characteristics research was very necessary and important. The equivalent soil spring model and structure-soil coupling model were established to compare and analyze the vibration characteristics based on different foundation simulation methods. The dynamic time history analysis was carried out base on the white noise excitation, to analyze the influence of the foundation participating mass on the vibration characteristics. The results show that: (1) The first two modes of the super-large centrifuge foundation are horizontal and vertical swings.(2) The vibration modes obtained by different foundation simulation methods are consistent, and the natural frequency difference is within 3%. (3) The foundation participating mass of the first two modes are 1.376 times and 0.998 times the total foundation mass respectively; considering the influence of the foundation participating mass, the vibration response amplitude of the structure is reduced by about 50%, and the peak frequency of the spectrum is reduced by about 2 Hz. The conclusions have guiding and reference significance for the vibration research of the embedded large scale power machine foundation.

 Based on the energy equilibrium, the computational formula of critical buckling length of multi-layer rock slope is derived. Considering interlayer and cross joints, the numerical manifold method is used to simulate the buckling evolution process of Malvern hills slope in New Zealand, and the theoretical calculation and numerical simulation results are compared with the field measured data. The results show that numerical manifold method can accurately simulate slope buckling failure process by preforming interlayer and cross joints. The process of slope buckling deformation and instability failure can be divided into interlayer dislocation-slight bending, slope toe traction-sharp uplift and accelerated sliding-landslide formation. Under the long-term action of self-weight, the evolution of slope buckling from formation to failure mainly includes three stages: initial bending, sharp bending and landslide formation. The angle between cross joint and slope normal is defined as β. Among the four kinds of cross joints with the angle β of 0°, 15°, 30° and 45°, the slope with 45° cross joint is most prone to sliping and bending deformation, the degree of buckling is the largest, and the number of time steps of slipping and bending is the least. When β is in the range of 30°~45°, the numerical simulation results are in good agreement with the reality.

A deformable spheropolygon-based discrete element method (DSEM) which combines the spheropolygon-based discrete element method (DEM) and the finite element method (FEM) is proposed. In this method, with the rounded discrete elements, the shape of the irregular blocks can be well characterized while the high efficiency advantage of particle discrete element method is also kept. The proposed method can not only eliminate the normal singularity at the corner but also improve the stability and simplify the contact judgment during contact force calculation. Meanwhile, the calculation model of the tangential contact force is also modified to improve the efficiency of contact force calculation. The DSEM breaks through the limitation of the rigid body hypothesis of the spheropolygon. Thus, the interaction between discrete elements with arbitrary shape can be accurately calculated, and the movement and deformation of the elements can also be simulated. Finally, three numerical examples including the dynamic response of statically indeterminate beam, the uniaxial compression test of irregular block, and hopper flow test is simulated using the DSEM to prove that the proposed method can effectively capture both the spatial motion as well as characteristics of elements (such as collision, separation and deformation) and their microscopic mechanical characterization.

With the gradual warming of the global climate, the possibility of large-scale sliding and collapse disasters of glaciers, large ice sheets or thicker ice layers are increasing. Research on the deformation characteristics of polycrystalline ice and establishing its constitutive model are of great significance for the disaster forecasting of polar regions. Based on the existing triaxial compression test data of artificial polycrystalline ice, it is found that the artificial polycrystalline ice has prominent characteristics of strain softening. The damage variable with equivalent plastic strain as the variable is proposed. By using the Mohr-Coulomb criterion as the initial yield function, and adopting the associated flow rule, an elastoplastic damage constitutive model that can reflect the strain softening characteristics of polycrystalline ice is established. The proposed constitutive model is verified by triaxial compression test data under different confining pressures and different temperatures, and parameter sensitivity analysis of some model parameters is carried out. The established elastoplastic damage constitutive model was written in the FLAC^3D software, and the embedded constitutive model was verified by the triaxial compression of a single unit. Then, the embedded elastoplastic damage constitutive model is used to perform triaxial compression on the cylindrical specimen. The simulation results are analyzed in detail. The results provide a theoretical and numerical basis for the stability analysis of glaciers and the multi field coupling study of glaciers.

The granular materials may have undergone full-domain quasi-uniform failure without significant local damage, i.e., diffuse instability, before reaching the Mohr-Coulomb plastic limit condition. Recent applications of network science tools in granular materials environments have provided interesting and novel insights to study their instability and failure. The numerical tests of the equal volume strain loading path on the granular systems with different initial porosities are carried out by using the discrete element method, it is found that the more loose the initial state of the granular systems, the more likely diffuse instability will occur. Using the theories and tools of network science to analyze the topological structure characteristics and evolution laws of the granular contact networks, it is found that the granular contact networks collapse completely when the diffuse instability of the granular materials occur. The granular system is divided into strong and weak contact systems to construct strong contact sub-networks, weak contact sub-networks and strong-weak contact sub-networks, and study the evolution of network features from the three sub-networks and the complete network. The results show that when the granular materials start to be in an unstable state, the part of contacts from the weak contact system disconnect first, leading to the strong contact system reducing its load-bearing capacity due to the loss of stable support from the weak contact system, and as the loading continues, the system leads to the full collapse of the contact structure through a non-local process of self-organization, i.e. the overall diffuse instability occurs. Therefore, the loss of partial weak contacts that precede the overall instability can be considered as a critical sign of diffuse instability of granular materials.

As the core issue of soil mechanics in the 21st century, the structure of undisturbed soil has been widely concerned. In particular, the mechanical behavior of structural damage in soft clay will pose a non-negligible impact on the foundation in offshore engineering. This paper takes the structural characteristics of the undisturbed submarine soil as the research object, and derives the numerical implementation format of the SANICLAY model considering the structure of the clay. Based on the analysis of the triaxial test results of the undisturbed marine clay, it is found that the marine soils have significant structural damage mechanical behaviors which means soil strength would reduce under static deviatoric stress. Through the Substepping Explicit Integral Algorithm method, the multi-yield surface soil constitutive model which can accurately reflect the structure damage of the marine soil is established. The evolutions of plastic potential surface and yield surface of soil under different consolidation conditions and shear conditions are studied. It is revealed that consolidation can reduce the degree of structural damage of the marine soil. Also, the occurrence of structural damage of the marine soil in the shearing process mechanism is illustrated. A series of analyses of the static bearing capacity of the bucket foundation that can consider the influence of the structured soil is carried out. The influence of the soil structure on the failure mode of the bucket foundation is analyzed. Through the parametric analysis of the structural damage factor, the change of the peak bearing capacity and the residual bearing capacity are studied; the concept of residual attenuation ratio is proposed to describe the residual bearing capacity of the foundation after the soil structure is completely lost. The relationship between residual attenuation ratio and the structural damage factor is established.

This paper presents the probabilistic analysis of landslides in spatially variable soil deposits, modeled by a stochastic framework which integrates the random field theory with generalized interpolation material point method (GIMP). Random fields are simulated using Cholesky matrix decomposition (CMD) method and Latin hypercube sampling (LHS) method, which represent material properties discretized into sets of random soil shear strength variables with statistical properties. The approach is applied to landslides in clayey deposits under undrained conditions with random fields of undrained shear strength parameters, in order to quantify the uncertainties of post-failure behavior at different scales of fluctuation (SOF) and coefficients of variation (COV). Results show that the employed approach can reliably simulate the whole landslide process and assess the uncertainties of runout motions. It is demonstrated that the natural heterogeneity of shear strength in landslides notably influences their post-failure behavior. Compared with a homogeneous landslide model which yields conservative results and underestimation of the risks, consideration of heterogeneity shows larger landslide influence zones. With SOF values increasing, the variances of influence zones also increase, and with higher values of COV, the mean values of the influence zone also increase, resulting in higher uncertainties of post-failure behavior.

This paper presents a method to generate random samples of soil dynamic shear modulus and dynamic damping curves with full consideration of the correlations of critical soil dynamic parameters to investigate the influence of their uncertainties on the engineering site seismic response in the implementation of equivalent linearization method. A one-dimensional (1D) equivalent linear site seismic response analysis program, which serves stochastic dynamic response analysis of the engineering site, has been developed in MATLAB. A 1D free field model for the typical layered engineering sites of site class II is established in this study. The target response spectra, which are defined with spectra of the outcrop corresponding to different earthquake return periods based on the acceleration response, are employed to generate artificial seismic records. These records are scaled down by ½ and referred to as input motions at the engineering bedrock for the 1D free field model. The numerical results show that the uncertainties of the critical soil dynamic parameters has significant influence on seismic response of engineering sites, which are highly related to the amplitude and the frequency aspects of the input ground motions as well as the fundamental periods of the engineering sites. The variations of the peak shear strain and the peak ground acceleration of the site, which reach 10% and 14%, respectively, increase with the amplitudes of the input ground motions. Besides, the variations of acceleration response spectra corresponding to the plateaus of the target response spectra and the fundamental periods of engineering sites exceeds 20% with the consideration of the uncertainties of soil dynamic parameters.

The line heat source method of soil moisture monitoring requires higher heating power. When the intensity of the heat source is unstable, the monitoring results are easily affected. To solve the shortcomings of the line heat source method, a mobile point heat source (PHS) method for soil moisture monitoring is developed in this study. This method uses the correlation between the thermal physical properties of soil and the moisture content to indirectly identify the moisture content by monitoring the cooling law of the PHS in the soil. Firstly, the heat transfer law of the PHS in the soil with evenly distributed moisture content was examined through numerical simulation. According to the characteristics of the cooling curves of the heat source, the moisture content discrimination index η was defined, and then the fitting relationship between the moisture content and the discrimination index was established. In addition, parameter analysis was carried out on the factors affecting the monitoring sensitivity. Then, numerical simulation of the PHS cooling law was carried out in the soil with unevenly distributed moisture content, and the moisture content discrimination index was calculated according to the time history curve at the cooling stage of the measuring point. After that, the moisture content distribution was inverted by the fitting formula of the moisture content and the discrimination index. The results show that the moisture content distribution inverted by the PHS method is in good agreement with the actual value, which verifies the theoretical feasibility of the method. Finally, the feasibility of the method is further verified by model tests.