To improve the liquefaction resistance of calcareous sand foundations, microbially induced calcium carbonate precipitation (MICP) technology combined with fiber reinforcement technology was proposed to treat the calcareous sand in the South China Sea. Based on dynamic triaxial tests, the dynamic behaviors of MICP and fiber-treated calcareous sand were studied. The dynamic strain, dynamic pore pressure, cyclic stress-strain response and dynamic elastic modulus were analyzed. Then, the strengthening mechanism of MICP and fiber on the mechanical properties of the treated calcareous sand was explored from the microscopic point of view, based on the scanning electron microscope (SEM) test results. The results show that: (i) MICP could improve the deformation resistance and liquefaction resistance of calcareous sands. Compared with the untreated calcareous sand samples, the dynamic strain and dynamic pore pressure of calcareous sand treated by MICP decreased by 95.74% and 92.46%, respectively. (ii) The addition of fibers further improved the reinforcement effect of MICP. Compared to the MICP-treated samples, the dynamic strain and dynamic pore pressure of MICP and fiber-treated samples decreased by 74.32% and 74.18%, respectively. (iii) MICP and fiber reinforcement technologies improved the deformation resistance and liquefaction resistance of calcareous sand subjected to cyclic loading by reducing the cyclic activity strength and energy dissipation, increasing the dynamic elastic modulus and reducing the decay rate of the dynamic elastic modulus. (iv) The results of the SEM test showed that MICP and fiber reinforcement had a synergistic effect on the improvement of the mechanical properties of calcareous sands. The incorporation of fibers provided more spots for bacterial adhesion and promoted the formation of calcium carbonate crystals, which not only increased the bonding strength between sand particles, but also enhanced the restraint of fiber nets by fixing fibers and sand particles together.

To further explore the fracture initiation mechanism of fracture grouting in typical sandy mudstone from Huainan and Huaibei mining areas in China, a conventional triaxial fracture grouting test device was developed, and the model test of fracture initiation pressure of slurry fracturing in similar material of sandy mudstone was carried out. Based on the test results, the influences of rock strength and stress state on grouting fracture initiation pressure and fracture propagation pattern were analyzed, and the fracture initiation mechanism of fracture grouting in sandy mudstone was revealed. The results show that there is a positive correlation between the initiation pressure and the compressive strength of rock; the larger the compressive strength of the rock is, the more complex the fracturing path is. The sensitivity of fracture initiation pressure to confining pressure is much greater than that of axial pressure; the larger the stress difference Δσ = σ _V −σ _H is, the more regular the fracture shape is. Under the triaxial condition of pore pressure, the rock tensile strength determined by slurry fracturing method in sealed open hole section is approximately 2.5 times the uniaxial tensile strength. The research results can provide a reference for the design and construction of fracture grouting in similar rock strata in the future.

 A series of triaxial tests was carried out under coupled cyclic-seepage loads for Tianjin coastal soft clay, and the variation of permeability in different loading stages was analyzed systematically. Combined with SEM and MIP, the evolution mechanism of permeability was elaborated. The results showed that under the coupling cyclic-seepage loads, the permeability of soft clay present three variation stages. With seepage loads increasing, the permeability increased initially and then decreased, but just reverse for increase of critical dynamic stress ratio. The evolution of permeability was caused by the adjustment of micro-features of pore shape, size, and distribution: for initial vibration, large compression of super large pores (D>2.5 μm) between particles occurred and pore shape varied little, leading to the linear reduction of permeability; at the medium loading stage, the large particles were broken, and the newly formed small particles were densely filled between the large particles, inducing a large number of “compact and zigzag” small pores (0.05 μm <D <0.1 μm), which led to the slow decrease of permeability; at later loading stage, the structure was compact and stable, and permeability was basically unchanged. For the unstable deformation, the “strips” like macropores were re-formed between the particle clusters (aggregates), and the permeability increased. The results can provide a theoretical basis for the determination of the permeability in the fluid-solid coupling analysis.

After sandstone is subjected to high temperature, the macro and micro properties will change to different degrees. 400 ℃ and 1 000 ℃ are two important nodes in the change of the macro and meso properties of sandstone. In order to further study the influence of heating rate on the physical properties, mechanical properties and internal meso-fracture of sandstone, the uniaxial compression experiment of sandstone under different heating rates was carried out with 350 ℃ and 950 ℃. The whole process of uniaxial compression was monitored by acoustic emission, and scanning electron microscope was used to analyze the meso-morphology of destructed sandstone. After treated at different heating rates, 350 ℃ sandstone has little change in the mass, volume, density and longitudinal wave velocity, while 950 ℃ sandstone decreased significantly in the mass, density and longitudinal wave velocity, and increased remarkably in the volume, and the higher heating rate, the smaller change rate. The stress-strain curve, stress-volume strain curve, compressive strength and elastic modulus of the 350 ℃ sandstone are virtually unaffected due to the heating rate. The stress-strain curve of the sandstone sample at 950 ℃ is upwardly biased with the increase of the heating rate, the compressive strength and elastic modulus first increase and then reach a constant value; the cumulative ring-down counts of acoustic emission of sandstone at 350 ℃ and 950 ℃ have a tendency to decrease with the increase of heating rate. When the temperature is 950 ℃ and the heating rate is 1 ℃/min, the cumulative ring-down counts of sandstone and the sudden acoustic emission area are the largest; scanning electron microscopy analysis of sandstones with different heating rates showed that heating rate has little effect on the mesoscopic morphology of 350 ℃ sandstone; with the decrease of the heating rate, the number of microcracks and micropores of 950 ℃ sandstone will  increase, the volume size of microcracks and micropores will also increase.

The triaxial strength envelope of rocks is usually nonlinear, and the shear strength parameters obtained by the linear regression method (LRM) are highly sensitive to confining pressure. In order to enable LRM to consider the influence of confining pressure on the estimation of shear strength parameters, the confining pressure effect coefficient of triaxial strength of rocks is defined. An exponential function is constructed to express the relationship between the coefficient and confining pressure, which is also introduced into the correction of LRM. A linear regression method considering confining pressure effects (CCPE-LRM) is proposed. At the same time, a rationality test method is proposed, and a distance coefficient is defined as an index to characterize the difference between the estimated and actual values of shear strength parameters. Through the verification and analysis of the triaxial strength data of various types of rocks in the published literature, the results show that the distance coefficients of various rocks are small, and the shear strength envelopes obtained by CCPE-LRM are all close to the Mohr circles in an approximately tangent state. It indicates that the shear strength envelope obtained by CCPE-LRM can replace the ideal shear strength envelope to a certain extent, and the shear strength parameters estimated by this method are in good agreement with the theoretical shear strength parameters. These prove that CCPE-LRM LRM has a good applicability.

Cushion materials can effectively reduce the impact load acting on the rigid protective structures such as shed tunnel and improve the impact resistance of the structures. In order to investigate the variation of cushioning performance of recycled concrete aggregate (RCA) under successive impacts, drop weight impact tests and discrete element simulations are carried out. Test results show that compared with the quartz sand cushion layer, the transmitted load at the center of concrete shed for RCA under the first impact reduces by 83%, and the transmitted load is distributed more uniformly. With the increase of impact times, both the cushioning performances of RCA and quartz sand deteriorate. For the sixth impact, the maximum transmitted loads at the center of concrete shed for RCA and quartz sand are 11.2 times and 1.4 times larger than those of the first impact, respectively. Furthermore, the cushioning performance is strongly influenced by particle shape. The numerical simulation results show that if the proportion of long particles increases from 0% to 100%, the rotation angle and translation distance of the particles decrease by 40% and 20%, respectively, and the maximum drop weight impact load increases by 37%. The inter-locking effect between particles increases with the irregularity of particle shape, which limits the rotation and translation of the particles, and increases the drop weight impact load and the transmitted load on the concrete slab. The research results may provide theoretical basis and engineering guidance for recycled concrete aggregate as a new type of eco-friendly cushion.

The development of marine energy is gradually moving towards the deep sea. Large offshore platforms at deepwater areas put forward a higher requirement for the bearing capacity to the mooring structures. Aiming at the problem of insufficient bearing ratio of traditional torpedo anchors, we developed a novel deepwater grouting torpedo anchor. The anchor drives the grouting pipe into the seabed, and then grouts into the seabed; the grout squeezes the soil and forms a grouting consolidation block around the anchor; thereby, the pullout resistance of the anchor will be greatly improved. The model tests were carried out using the self-designed marine anchor grouting and pulling test system, and the effects of different grouting quantities on the grout diffusion characteristics and the bearing characteristics of the anchor were studied. The results show that the grout can better wrap the anchor, grout block is inverted cone and bond closely with the anchor, and they can bear the upper load together. The maximum bearing ratio of grout block can reach 24.6, much higher than 2.4-4.1 of traditional torpedo anchors, thus verifying the feasibility of deepwater grouting torpedo anchor. With the increase of grouting quantity, the cross-sectional area and overall height of grout block are increased, and the overall bearing capacity of the grouting torpedo anchor also is enhanced.

Soil-water characteristic curve (SWCC) plays an important role in defining the hydro-mechanical behavior of unsaturated soils. Biochar has the properties of porous structure, high specific surface area and high adsorption. The hydraulic characteristics of biochar-amended soil may change due to the influence of natural environmental factors when applied as the cover layer of landfills. In order to study the effect of biochar content on the water retention behavior of biochar-clay mixture in full suction range, the suction of samples was controlled by vapor equilibrium technique (suction range 3–368 MPa), filter paper method (suction range 0–40 MPa) and pressure plate method (suction range 0–1.5 MPa), and the water content and saturation degree of samples after suction equilibrium were determined. The soil-water characteristic curve of biochar-clay mixtures was obtained in the full suction range. The results showed that: (1) The soil-water characteristic curve in the full suction range of biochar-clay mixtures was effectively expressed by the three suction testing methods. (2) Biochar can affect the water retention behavior of clay, but within a certain range of suction, the water retention behavior of biochar-clay mixtures was also related to the pore structure and the morphology of water in the pores. (3) As measured by the pressure plate method, the air intake value of samples decreased as the biochar content increased. When the suction value was less than the air intake value, a horizontal section appeared in the curve, and the samples were always in the saturated state. The greater the content of biochar, the better the water retention of the sample. (4) The relationship between the water retention capacity of biochar-amended clay and biochar content was explained by the microscopic structure of the biochar-clay mixture and the distribution form of biochar in clay.

Internal erosion is a phenomenon that fine particles migrate through the channels within coarse matrix under seepage flow. Previous studies mainly focused on the internal erosion under steady hydraulic gradient, while the behavior and mesoscopic mechanism of internal erosion under fluctuating hydraulic condition were paid little attention. In this study, a setup of transparent soil seepage test was developed. Seepage tests of two kinds of soils with different internal stabilities were conducted under steady and fluctuating hydraulic conditions respectively to investigate the internal erosion behaviors under fluctuating hydraulic condition. The macroscopic experimental phenomenon showed that, when the hydraulic gradient exceeded the critical hydraulic gradient, the increase of the hydraulic conductivity under fluctuating hydraulic condition was faster than that under steady hydraulic condition for internally unstable soil, manifesting that hydraulic fluctuation aggravated the migration of fines. In order to further reveal the mesoscopic mechanism, a three-dimensional reconstruction method was employed to rebuild the mesoscopic fabric of soil based on the two-dimensional cross-sectional images obtained by the planar laser scanning; and a three-dimensional visualization digital model including coarse matrix, inter-granular pore channels and fine particles was established. By observing the distribution of fine particles in pore channels, it was found that fine particles might clog and accumulate at narrow pore throats under steady seepage. While the perturbation caused by hydraulic fluctuation could break these weak stable structures of clog and accumulation, and then restart the migration process of fine particles.

The development of vertical cracks in loess slopes often affects slope stability. Compared with the plane strain mechanism, the slope stability analysis under the three-dimensional (3D) failure mechanism is closer to the actual slope instability. Based on the upper bound method of plastic limit analysis, different failure mechanisms (face failure, toe failure and base failure) of 3D loess slope with pre-existing cracks are considered, the energy balance equation and its dimensionless critical height expression γH/c are established, and the upper bound solution of critical height is obtained by random search method. The effects of constraint width, slope angle, internal friction angle and crack depth on the critical height of 3D vertical cracked loess slopes are analyzed. The results indicate that for the toe failure mechanism, the critical height decreases with the increase of crack depth, and the increase in crack depth no longer affects the critical height after reducing to the critical crack depth (δ /H)_min. The critical crack depth increases with the increase of slope angle β and decreases with the increase of internal friction angle φ. When the constraint width B/H<0.8, most of the failure mechanism is of face failure. When the constraint width  B/H =0.8 , internal friction angle φ =10°, and the constraint width B/H=0.6, internal friction angle φ =15°, the failure mechanism of the slope gradually transits from the face failure mechanism to the toe failure mechanism. The loess slope with vertical cracks has a smaller critical height than the intact slope. The constraint width and internal friction angle can affect the failure mechanism of 3D loess slopes.

The variation of temperature will lead to the change of physical-mechanical properties of the soil, and in some engineering cases, saturated clay will be subjected to non-isothermal distribution condition. Therefore, to address the one-dimensional consolidation problem of saturated clay under non-isothermal distribution condition, a one-dimensional consolidation governing equation under single-stage linear loading is derived by some assumptions, in which the more general partial drainage boundary is considered. In addition, the analytical solution for governing equation is obtained by using separation variable method. By comparing the proposed analytical solution with the existing analytical solution and the finite difference solution, the correctness of the proposed analytical solution is verified. Based on the proposed analytical solution, the effects of temperature gradient, partial drainage boundary parameters and loading time on the one-dimensional consolidation behaviors of saturated clay are analyzed with an example. The results show that the larger the temperature gradient is, the greater the permeability of the soil becomes, and the faster the consolidation rate of the soil gets. The larger the partial drainage boundary parameters are, the smaller the excess pore water pressure of the soil at the same time becomes, and the larger the average consolidation degree of the soil gets. The average consolidation degree of the soil decreases with the increase of loading time, which is mainly due to the external loading applied to the soil in the loading stage is smaller than the final loading, but the extension of loading time can reduce the maximum excess pore water pressure in the soil to a certain extent.

In the conventional triaxial compression test, the stress-strain relationship of strong structured cohesive soils under a low confining pressure will show strain softening and is usually accompanied by plastic deformation. Generally, the internal structure damage of soil is the main cause of strain softening. Using classical plastic theory to describe the strain softening characteristics of materials may violate the Drucker's stability hypothesis, and cannot describe the plastic deformation during unloading. Based on the modified Cam-clay model and the plastic hardening rule proposed by Li and Meissner, an elastoplastic two-surface model is established. This model divides the stress-strain curve into strain hardening stage and strain softening stage at the peak stress point and the divided two stages are analyzed as independent loading events respectively. Meanwhile, a new structural parameter is proposed to characterize the degradation of plastic stiffness caused by soil structure damage during loading. Additionally, the comparisons between simulated and measured results of saturated structural clay in different consolidation states indicate that the model can describe the stress-strain curves and stress path curves with high accuracy and can give reasonable and good simulations of strain softening of structured clays in undrained condition.

Under the background of the development needs of energy geotechnical engineering, the research on the temperature effect of soil engineering characteristic has received extensive attention from scholars. Aiming at the shortcomings of the existing theoretical research on cyclic variable temperature thermal consolidation, this paper gives a relationship between the change of the soil preconsolidation pressure and the number of temperature cycles under the condition of cyclic temperature change to calculate the consolidation and compression of soft soil after repeated temperature changes. On this basis, the modified Terzaghi consolidation formula considering the cyclic temperature change is derived to predict the change of pore pressure and consolidation settlement during the whole cycle of temperature change. Finally, the reliability of the calculation model is verified by comparing with the unit test results. The research indicates that under the coupling action of cyclic temperature change and instantaneous load, the settlement deformation and pore pressure of the soil will change with the number of temperature cycles, and the degree of influence is related to the number of cycles; the proposed thermal consolidation model provides certain theoretical support for the analysis of geotechnical engineering problems involving cyclic temperature variations.

Based on the piece-linear finite difference approach, a nonlinear consolidation model, called SC1, of stone column composite foundation considering large strain was developed. The model has the ability to analyze the consolidation of pile-soil composite foundation under the conditions of free stress and equal strain, and to consider well resistance, smear area, self-weight of pile-soil, variable load, as well as the nonlinear changes of pile-soil parameters in the consolidation process. The model was validated against the equal strain analytical solution and experiment. Under the condition of small strain, the numerical solutions of the model are in good agreement with the analytical solution of pile-soil composite foundation with or without well resistance and smear area. Under the conditions of large strain and nonlinear consolidation, the model calculation results are basically consistent with the experiment data. Then, the model was used to predict a practical engineering, and it was found that with the extension of consolidation time, the difference between the calculated values of the model based on free stress and equal strain increases gradually, and the field measured value is between the numerical solutions of the model with free stress and equal strain.

The movement behavior of soil particles near pile foundation is closely related to the macroscopic mechanical performance, which is of great significance to reveal the interface shear mechanism. By using the self-developed large-scale direct shear instrument and the 3D-DIC full field displacement measurement system, cyclic shear tests of interface between steel plate and calcareous were carried out to examine the motion behavior of sand particles near the interface. The results show that the peak interface shear stress and the developed friction angle of interface increase with the number of cycles, and shear shrinkage is the main characteristic of volumetric deformation. The range of left-right movement of calcareous sand particles is inversely proportional to their vertical distance from the interface. The position of calcareous sand particles gradually moves to the positive shear direction with the number of cycles. At the end of the test, the calcareous sand particles in the left area of the upper shear box move a large distance towards the positive shear direction. Calcareous sand particles move up and down regularly in a single cycle, which is mainly characterized by downward movement. The downward movement displacement of calcareous sand particles far from the interface is greater than that closer to the interface. The movement speed of calcareous sand particles shows a slow-fast-slow change law when shearing along the single direction. The volume deformation characteristics of calcareous sand on the right region of the upper shear box are more obvious than those on the left region. The displacement value of the grid and the number of missing grids increase with the number of cycles, and tend to be stable in the later stage of the test. At the end of the test, the thickness of the breakage zone is 6.21 mm.

Due to some problems such as difficulty in reserving pipe jacking construction holes, the inclination of open caisson and the insufficient bearing capacity of the support structure in the traditional support structure during pipe jacking construction, the efficiency and safety of pipe jacking construction will be seriously affected. To address these problems, a new type of profile steel- polymer composite fabricated support structure suitable for pipe jacking work shaft is developed. Through the combination of actual engineering field test and finite element numerical simulation, the soil settlement deformation around the work shaft and the mechanical response of the support structure during pipe jacking construction are analyzed, and the reliability of the new support structure for pipe jacking construction is verified. Finally, the main controlling factors affecting the mechanical properties of the support structure of the work shaft are obtained through an orthogonal simulation test. The results show that the spacing of support piles is the main controlling factor affecting the mechanical properties of the new support structure, and in the process of short-distance pipe jacking, the soil around the work shaft has different degrees of settlement, and the surface settlement in the jacking direction is the largest, and the surface settlement in the sidewall direction is the smallest, and the influence range on the surface settlement is about 2.7 times of the jacking distance. Moreover, the stress of supporting pile increases with the increase of pipe-soil interface friction, and the stress of supporting pile at the entrance is the largest. In the long-distance pipe jacking construction, the stress of the jacking surface is large in the early stage of pipe jacking. With the increase of the jacking distance, the stress of the sidewall and back wall increases, which is higher than that of the jacking surface. The research results can provide favorable suggestions for the optimal design of a new support structure of pipe jacking work shaft.

Aiming at the lack of quantitative judgment on the spatial distribution of the toppling deformation fracture surface of the anti-dip layered rock slope, this paper develops an independent cantilever beam model and an independent simply supported beam model for the rock slab toppling and breaking based on the analysis of the geological prototype and deformation mechanism. The proposed models can consider the self-weight of the rock layer, the weight of the overlying rock layer, the lateral pressure, and the friction between the rock layers. The maximum tensile stress failure criterion of the slab beam was used to deduce the critical fracture depth formula of the rock stratum in each stage of the toppling deformation. The proposed method was verified by geological prototypes. The slope shape parameters of each stage of toppling deformation were obtained by centrifugal test, and the fracture depth of each stage was quantitatively evaluated in this paper. The research shows that the theoretical model can calculate the fracture length of rock formations at various stages, such as the shear dislocation between layers of toppling deformation, weak toppling failure, and intensive toppling failure. The fracture length is positively correlated with the internal friction angle, the thickness, and the tensile strength of rock strata, and is negatively correlated with the distribution elevation of rock strata, tensile stress and the weight of rock beam. According to the mechanical parameters of each stage of the toppling deformation, the distribution positions of the fracture surfaces of the toppling rock strata at all levels are calculated, and the results are consistent with the geological prototype and centrifugal test results.

At present, for the problem of poor reinforcement effect in the process of vacuum preloading using band drains, most of the existing studies focus on the vacuum preloading loading mode, while there is a lack of theoretical and experimental studies on the emerging drains of different structure types. In this study, three types of band drains are selected for vacuum preloading model tests, and the reinforcement law and effect of different band drains in the process of vacuum preloading are compared. The test results show that the soil moisture contents of soil treated by double-sided connected drains and straw band drains are reduced by 9% and 5% respectively as compared with the conventional band drains, and the vane shear strength is increased by 1.7 kPa and 1 kPa on average. It means that the double-sided connected band drains has better anti-silting performance, and the straw band drains can achieve better reinforcement effect than the common band drains while having the characteristics of environmental protection, which provides a new solution to solve the problem of poor reinforcement effect of vacuum preloading.

The soft soil usually exhibits obvious nonlinear compressibility and permeability characteristics during the consolidation process. At the same time, the clogging effect of vertical drains often causes the well resistance to change with depth and time during the consolidation process. However, the analytical solution for nonlinear consolidation of soils with vertical drain, in which the variation of well resistance over time and depth can be considered, is still rarely reported in the literature. In this study, semi-logarithmic models between the void ratio and the effective stress, and between the void ratio and the permeability coefficient are introduced to describe the nonlinear consolidation characteristics of soils, and a nonlinear consolidation model of soils with vertical drain, which can simultaneously consider the time- and depth-variation of well resistance and the influence of smearing, is developed, then the analytical solution of this consolidation model is obtained by the method of separated variables. The consolidation calculation results derived here under specific parameters are compared with the laboratory tests data, and the existing vertical drains consolidation solutions to verify its reliability. Finally, a large number of calculations and analyses have been carried out on the nonlinear consolidation behavior. The results show that the more obvious the linear decay of the vertical drain permeability coefficient with depth is, the slower the consolidation rate of soils with vertical drain is. Considering the exponential decrement of the vertical drain permeability coefficient with time, the consolidation rate of soils with vertical drain is much slower than that with consideration of the vertical drain permeability coefficient remaining constant over time. When the external load is constant, the consolidation rate of the vertical drain foundation decreases with the ratio of the soft soil compression index (cc) to the permeability index (ck) increases. When the value of cc/ck remains constant, the consolidation rate of the vertical drain foundation increases with the external load increases. Among the three variations related with horizontal permeability in smear zone, the vertical drain consolidation rate is the fastest under the parabolic variation mode, the next is the linear variation mode, and the vertical drain consolidation rate under the constant variation mode is the slowest. The influences of smear zone on consolidation behavior are not affected by the change of well resistance and the nonlinear consolidation characteristics of soils.

The soil-water characteristic and microscopic mechanism of heavy metals arsenic, cadmium and their composite contaminated soils were studied in this paper. The evolution law of soil-water characteristic curves of contaminated soils was investigated by using centrifuge method, and the microscopic characteristics of contaminated soils was determined by using Zeta potential, NMR and SEM tests. The experimental results show that there is a link between microscopic characteristics and macroscopic soil-water characteristics of the contaminated soils, that is to say the thinner the thickness of the diffused double layer of soil particles, the weaker the water holding capacity of soil, the lower the absolute value of Zeta potential, the larger pores corresponding to large agglomerates, the smaller the air entry value of matrix suction, otherwise the opposite. The type and concentration of heavy metals affect the soil-heavy metal interaction, leading to changes in microscopic characteristics and soil-water characteristics of contaminated soils. When the concentration of arsenic in contaminated soils increases, the dominant reaction changes from electrostatic adsorption of sodium ion to specific adsorption of arsenate, leading to the thickness of the diffused double layer first decrease and then increase. When the concentration of cadmium in contaminated soil increases, the dominant effect changes from crystal precipitation of cadmium carbonate to electrostatic adsorption of cadmium ion, both of which compress the double electric layer but the former is more significant. The dominant role in the composite contaminated soil is the electrostatic effect of cadmium ions and the specialized adsorption of arsenate ions, which have an opposite effect on the thickness of the diffused double layer.

The strength characteristics of the interface between saturated clay and structure were analyzed by triaxial instrument. Shear strength and excess pore water pressure at the interface between saturated clay and structure were measured by prefabricating an inclined and drilled structure surface, forming a triaxial composite sample with saturated clay. Compared to the interface direct shearing test which can not distinguish the shearing rates effect and drainage effect of the interface strength characteristics, the proposed method can accurately control the drainage conditions and clarify the influence of the shearing rates on the interface strength. Triaxial consolidated undrained interface shear tests with various surface roughness and shearing rates were carried out. Direct interface shear tests under various shearing rates were also conducted. Results show that the shear strength and excess pore water pressure increase with the increase of the roughness of the structural surface under the same confining pressure. The shear strength and the axial strain required for the stability of excess pore water pressure at the interface increase with the increase of shearing rates. Strict control of drainage conditions and accurate measurement of excess pore water pressure at the interface are of great significance for measuring the interface friction angle between saturated clay and structure.

In order to solve the problems of low drainage efficiency and uneven consolidation effect of muddy soil during traditional electro-osmotic drainage process, a new idea of using anionic polyacrylamide (APAM) combined with electro-osmosis method to treat muddy soil was developed from the perspective of changing the water holding characteristics of soft clay particles. The self-made one-dimensional electro-osmotic consolidation test device was used to explore the mechanism of flocculation- electroosmosis method and the influence of different mixing ratios of flocculant on the reinforcement effect. The results show that APAM reduces the thickness of the bound water film on surface on soft clay particles as compared with the traditional electroosmosis method, significantly improves the early electroosmotic drainage rate and cumulative drainage of muddy soil, thus lowering the average energy consumption coefficient of electro-osmotic method. Meanwhile, the “adsorption bridging” effect of the macromolecule long chain of flocculant enhances the cohesive force and flocculation deposition effect of soil particles, which effectively alleviated the cathode clogging caused by the migration and agglomeration of fine clay particles. The shear strength of muddy soil was increased greatly after treatment, and its uniformity was also significantly improved. When the mixing ratio of the flocculant APAM was 0.30%, the highest efficiency of electro-osmotic drainage and the optimal consolidation effect of muddy soil were achieved.

The density and stress state significantly impact on the sand stiffness. Many of hardening soil models used for geotechnical computation are based on Duncan-Chang model and do not consider the influence of density on the soil stiffness. In course of triaxial compression of very dense or loose sands, the shear strains rise induces significant changes in density. In order to evaluate the effects of grain size distribution, density, and stress state on stiffness, the results of 962 isotropic triaxial tests on soil samples from 15 Moscow and Minsk construction sites were processed using statistical and regression analysis. As a result, empirical equations enabling evaluation of the effects of density and stress state on stiffness of sands with different particle size distribution were proposed. Comparative analysis of tests performed on alluvial and continental soils from Europe, India, and the United States sites showed that the sand stiffness is in the same range as sands from Moscow and Minsk sites. Proposed equations can be applied for preliminary estimation of the stiffness parameters for finite element method calculation and also can be used in geotechnical models that allow variability, horizontal and vertical distribution of stiffness to be taken into account. Additionally, the semi-empirical relationship based on the Duncan-Chang model, is proposed. The relationship provides more realistic results for loose and extra dense sands affected by large deformations and/or complex loading paths, when the changes in density influence soil stiffness. Generally, geotechnical engineers may utilize the obtained results to apply them to design of complex soil models.

The discontinuities in rock mass could directly affect the strength, deformation and fracture patterns. Investigation of the distribution information and the orientation of discontinuities in jointed rock mass is the fundamental part for rock engineering. This paper proposed a fast identification and analysis method of joint traces information based on the Hough detection method. The orientation information of the joint traces could be automatically recognized and analyzed based on the image edge detection of rock mass image. The research results show the feasibility of the proposed method when detecting the left-inclined, right-inclined lines and crossing straight lines. Extraction of the joint traces of discrete fracture network model and in-situ case were analyzed and compared. The information of orientation and dip angle of the joint traces was effectively identified. The feasibility of the proposed method in identifying the joint traces was discussed by analyzing the sensibility of the identifying parameter of k. The proposed Hough detection method could provide a novel application method for the identification of joint traces information of rock mass.

Pumping of confined water is one of the main problems faced by deep foundation pit engineering. And group well pumping test is the main method to reasonably analyze the drawdown of confined water and surface settlement around foundation pit engineering, which is of great significance. A large-scale deep foundation pit pumping test in the area of a terminal in Shanghai was selected as an example in this study. Combined with the engineering geology and hydrogeological conditions of the site, the confined water level change and surface settlement during the group well pumping tests were analyzed. The influence of the drawdown of confined water on soil layer compression and ground settlement were investigated. The results showed that within the monitoring range of 300 m, the maximum ground settlement was 104.9 mm, the maximum drawdown was 21.85 m, and the ground settlement caused by the drawdown per meter was about 5mm. The maximum compression of 7th soil layer was 68.4 mm, and the compression caused by one meter of drawdown was about 3 mm. The ratio of settlement to drawdown tended to decrease with the increase of distance, and within the range of 40−310 m from the center, the ratio of settlement to drawdown was 4.22−1.17 mm.

It is important to study failures of rocks under dynamic loads for expounding mechanisms of geological disasters and for predicting and preventing these disasters on theoretical and practical aspects. Owing to advantages of numerical simulation, numerical methods applicable to modeling dynamic fracturing processes must be especially emphasized. Based on the combined Lagrangian-discrete element method, a continuum-discontinuum method considering the dynamic constitutive model was presented, in which the Zhu-Wang-Tang constitutive model was used to replace the generalized Hooke law. The continuum-discontinuum method considering the dynamic constitutive model was validated through modeling uniaxially compressive experiments of sandstone rock specimens for different loading velocities. Evolution of the number of crack segments with the longitudinal strain of the rock specimen was investigated, and evolution of the minimum principal stresses of nodes at the longitudinal symmetric line was also monitored. Deformation-fracturing processes of granite specimens for different loading velocities were modeled, and fracturing mechanisms of rock specimens were revealed. The following results were found. Shear bands include en echelon shear cracks. The minimum principal stress of the node exhibits a fluctuant decrease, followed by an increase in the oscillation form. The increasing stage corresponds to the strain-softening stage of the rock specimen. A large oscillatory amplitude of the minimum principal stress is found for the separating node, which is due to the fact that large stress waves are induced by node separations and contact between elements. Shear separations of nodes occur due to concentrations of the minimum principal stresses at the shear band tip. Motion of the triangle wedge of the rock specimen leads to tensile separations of nodes whose stress states are similar to those of the compact tension experiment.

Ultimate bearing capacity has always been a difficult and hot issue in mining and rock and soil fields, which seriously affects the safety and stability of slope and adjacent slope structures. Based on the upper bound theorem of limit analysis, the failure mechanism of heterogeneous layered slope with rigid multi-sliders was established in three modes. The upper bound solution of slope ultimate bearing capacity was deduced, and the optimal value was obtained by sequential quadratic programming algorithm (SQP). The north slope of Sancha mine was taken as the engineering background to verify effectiveness of the proposed method by comparing with the numerical method, and then the influence analysis of two parameters of different slope angles and the distances between dump and slope shoulder was carried out. The results were concluded as follows. (1) The results of the proposed method are in good agreement with those of numerical method, indicating that the proposed upper limit solution of slope ultimate bearing capacity is reasonable and effective. (2) The ultimate bearing capacity of slope has a linear negative correlation with slope angle and a linear positive correlation with the distance between the dump and the slope shoulder. Compared with the distance between the dump and the slope shoulder, the slope angle is more sensitive to the bearing capacity of slope. (3) The change of slope angle has a great influence on the slope failure mode, but the change of the distance between the dump and the slope shoulder has no obvious influence on the slope failure mode. (4) Both slope angle and the distance between the dump and the slope shoulder have an impact on the initial position and the overflow position of the slip surface. The initial position of the slip surface is greatly affected by the distance between the dump and the slope shoulder, but less affected by the slope angle. The overflow position of slip surface is greatly affected by slope angle but less affected by the distance between dump and slope shoulder. Relevant research results are expected to provide theoretical support for slope and adjacent slope foundation design.