Based on the non-uniform characteristics of rock friction and sliding deformation field, the friction and sliding laws of creep-slip and stick-slip were studied, respectively. By means of double-sided friction model experiment, using digital speckle correlation method as the observation method, the evolution and laws of the displacement field contour, the non-uniform statistics of the deformation field, the deformation energy density and the sliding velocity of the sliding surface in the processes of creep-slip and stick-slip deformation of rock were studied respectively. The results showed that: the distribution of contours in the surrounding rock displacement field could better reflect the characteristics of sliding surface resistance, in which the contours in the strong resistance sliding area were arch-shaped and distributed sparsely, while the contours in the weak resistance sliding area were parallel and distributed densely. In the creep-slip process of rock, the non-uniform statistics showed the characteristic of fluctuation growth, while in the stick-slip process of rock, the non-uniform statistics showed the characteristic of mutation and jump. In the creep-slip process of rock, the sliding speeds in different areas were in alternating state of acceleration and deceleration. In the stick-slip process of rock, the sliding velocities in different areas were abrupt. In the creep-slip process of rock, the deformation energy densities in different areas were all in the fluctuation state of accumulation and release, while the deformation energy densities in different areas in the process of stick-slip were abrupt.

As a waste material generated during coal mining and washing, coal gangue is often used for filling roadbeds. The compacted coal gangue has a dual-porosity structure, which usually leads to bimodal soil-water characteristic curves (SWCC). SWCC is closely related to the permeability coefficient of unsaturated soils, which has an important influence on the water migration inside the roadbed and the long-term serviceability of the roadbed. In order to investigate the influence of compaction degree, silt content and maximum particle size on bimodal SWCCs, a series of pressure plate tests was conducted on compacted coal gangue samples. The experimental data was fitted by a bimodal SWCC function model, and the variation of fitted parameters was analyzed. The test results show that when the silt content is 5%, samples with different compaction degrees have bimodal SWCCs. When the silt content is 50%, the SWCCs of samples change from bimodal to unimodal with the increase of compaction degree, so it can be inferred that there exists a critical value of compactness between 0.90 and 0.95. Increasing compaction degree or silt content, or decreasing maximum particle size will reduce the difference of step height in SWCCs. With the increase of compaction degree or silt content, the values of model parameters , (parameters related to the air-entry value) and , (parameters related to drainage degree) decrease gradually, that is, the air-entry values and the water holding capacity of both macro-pore part and micro-pore part increase.

As an alternative medium for the underground disposal of radioactive waste, claystone will be in the complex conditions of thermo-hydro-mechanical coupling for a long time. In order to study the long-term stability of surrounding rocks, a series of heating-cooling drainage creep tests on claystone was carried out under different confining pressures and deviatoric stresses, and the following conclusions were drawn. The rise of temperature will increase the creep rate of claystone, and extend the time of decay creep stage. But during the cooling process, the samples mainly experience shrinkage deformation without obvious creep deformation being observed. The decrease of confining pressure and the increase of deviatoric stress will increase the creep rate of claystone, and this effect will be significantly aggravated with the increase of temperature. Based on the experimental results, creep hardening, creep damage and thermal damage were introduced on the basis of Perzyna overstress theory, and a coupled thermo-hydro-mechanical creep model for claystone was established. The model was numerically implemented by ABAQUS and its subroutines. The comparison between the simulation results and test results demonstrates that the model can effectively describe the creep characteristics of claystone under thermo-hydro-mechanical coupling.

The method of rainfall infiltration analysis directly affects the prediction and prevention of rainfall-induced landslides. Green-Ampt (GA) model, which has clear physical meaning and few parameters, has been paid more and more attention in the analysis of rainfall-induced landslides. However, this method ignores the existence of the unsaturated layer of the wetting layer and the seepage of the saturated layer, which affects the calculation accuracy. In view of the above deficiencies, the LSGA model is established based on the stratified hypothesis and the saturated layer seepage, and the expression of slope stability coefficient is established. All results show that LSGA model can be simplified to GA model for infinite slope without considering the stratified hypothesis of wetting layer, which indicates that GA model is a special case of LSGA model. The slope infiltration depth and instability time of GA are obviously behind the LSGA model. The saturated layer seepage has slight effect on the characteristics of the wetting layer, but has a great influence on the stability of slope. On the contrary, the effect of slope length on wetting layer characteristics is important, but the effect on slope stability is slight. All results obtained by using LSGA model and the stability evaluation method are basically consistent with the phenomena revealed by the model test, which proves that the method has better accuracy and reliability than others.

The foundation pit excavation of a power plant located along the Yangtze River in Jiangsu province is selected to study the interaction mechanism between piles and soils during excavation of foundation pits in deep silty soft soil. Thus an indoor centrifugal model test with the similarity ratio of 1:50 is designed. The influence of foundation pit excavation on existing pile and surrounding soil in deep silty soft soil are analyzed from different aspects including the pile strain, pile displacement, pile top displacement, surface settlement and soil deformation influence range, pile bending moment and pore water pressure. Results from the centrifugal test and the excavation of the foundation pit in situ are compared and analyzed. It shows that when the shear strength of silty soft soil in the upper part of the layered foundation is relatively high, the pile foundation is subjected to a large force and it is prone to the breakage accident during the excavation process. Two extreme values of pile strain occur near the excavation depth and the interface between the silty soil and the underlying soil layer. Due to the influence of the pile, the pore water pressure of the soil near the excavation face changes smoothly, but the pore water pressure of the soil after the pile changes drastically with the excavation. The interaction between piles and soils mainly lasts 48 hours after excavation before the restoration of stability. The test results match with the field measured data, which can provide a reference for the design and construction process of the foundation pit in deep and thick soft soil.

The weathered rock material-tire shred lightweight soil has advantages such as low density and high permeability, which could significantly reduce the structure deformations. However, the deformations of geosynthetics in this lightweight soil are still needed to be investigated. This paper presents a series of pullout tests on an innovative geosynthetics—sensor-enabled geobelts (SEGB). Different mass ratios of tire shreds (10%, 15% and 30%) and normal pressures (30 kPa, 50 kPa and 100 kPa) are also considered. With the reinforcement and self-measurement of SEGB, the distributed measurement on strain of SEGB could be realized via measurement of electric resistances. Based on the uniaxial tensile tests and direct shear tests, a bilinear model capturing the full stress-strain curves of SEGB and a hyperbolic model evaluating the geobelt-soil responses are developed, respectively. The two models are employed in the derivation of the load transfer equation of pullout process. Solved by finite difference method, the load transfer equation gives numerical results about the distributions of tensile force, strain, displacement and interfacial shear stress along the geobelt. The test results validate the numerical results, including the constitutive models and the solving method. There exists an optimal mass ratio of tire shreds for the best frictional characteristics of geobelt-soil interfaces. The values of tensile force, strain, displacement and interfacial shear stress reach the peak values at the front end of geobelts, then decrease along the geobelts and gradually remain stable. Under high normal pressures, the geobelts exhibit visco-plasticity with larger strain levels and smaller displacements. The interfacial shear stress shows a more even distribution under a low normal pressure.

Rock simulation is the core of the researches such as geotechnical engineering model test and geological core simulation tests. At present, however, the molding simulation results based on artificial materials are greatly different with that from the actual rock properties due to the limitations of existing similarity theory and technical approaches, especially for the molding simulation of soft rock. In this study, the natural red beds is taken as the raw materials and the traditional diagenesis simulation system is improved. The influences of temperature, pore fluid pressure and overlying pressure are considered herein. The formation process of red bed is realized from the loose rock and soil particles to the rock and the engineering standard size soft rock cores are obtained. Based on the comparison results of diagenesis process, physical properties, chemical properties and mechanical properties between the natural red bed soft rock and the soft rock core that based on natural red bed materials, it is found that the simulated soft rock cores have similar properties with that of the natural red beds soft rock. This study breaks through the limitations where only certain properties can be generally satisfied from the artificial material similarity simulation, 3D printing or other methods. This study can provide a new manufacturing ideas and methods for the research of large demand soft rock core with differing functional requirements.

This paper presents an investigation into anti-sliding characteristics of high-pressure grouting steel-tube micropiles under actual stress condition. Full-scale model experiments were performed on landslides reinforced with a single high-pressure grouting steel-tube micropile and a group of micropiles, and with a single gravity grouting micropile as a comparison experiment. The results demonstrate that the root-shaped bonded bodies near sliding zone are formed due to the splitting of soil around the micropile by the high-pressure grouting. High-pressure grouting is able to improve soil mechanical properties significantly in landslides, enhance the resistance deformation capability of the pile bodies, decrease the bending deformation of piles, and leads to an increase of 152.6% for shear strength of the soil in the sliding zone. Comparing with the gravity grouting micropile, the horizontal ultimate loads of the landslides reinforced by a single high-pressure grouting steel-tube micropile and a group of micropiles increase by 37.8% and 71.2%, respectively. In the high-pressure grouting group piles, the horizontal forces and bending moments acting on the backward pile are maximum, followed by the forward pile, while those acting on the middle pile are minimum under the condition of limit state. The failure locations of the piles are characterized by the maximum bending moment. The failure mode of the concrete around the piles transforms from crush failure located at trailing edge to tension failure at leading edge of the landslide.

To analyze the optimal position of horizontal drainage sand blanket in reclaimed foundation, the case that a double-layer foundation with placement of a single sand blanket is considered, using the method of separation of variables, and the analytical solution of excess pore-water pressure and average degree of consolidation is obtained. Their validity is verified by degeneration and finite element method. The effects of the lower foundation permeability coefficient to the upper foundation permeability coefficient ratio (a), the lower foundation volumetric compression coefficient to the upper foundation volumetric compression coefficient ratio (b) and the lower foundation thickness to upper foundation thickness ratio (c) on the optimal position of the sand blanket are discussed. Finally, an example is given to demonstrate different consolidation efficiencies of the foundation when the sand blanket is placed at different positions. The results show that at the same time factor, when 1, the optimal position of the sand blanket moves downward with the increase of a, but when 1, the opposite becomes the case. The optimal position of the sand blanket moves downward with the increase of b when 1, and when 1, the opposite becomes the case. When the consolidation coefficient of the lower foundation is greater than that of the upper foundation, the optimal position of the sand blanket moves upward with the increase of c in the early stage of consolidation, and the opposite becomes the case in the later stage of consolidation. The calculation results show that when the average degree of consolidation of foundation reaches 90%, the sand blanket is placed at the optimal position, which saves a lot of time compared with the unpaved sand blanket.

In order to study the brittle characteristics and evolution law of the rock in the cold region, the freeze-thaw cycle test and triaxial compression test of the cyan sandstone were carried out. The brittleness evaluation index is used to quantify the brittleness of the cyan sandstone under the freeze-thaw cycle. Then the effects of freeze-thaw cycles and confining pressure on the brittleness of cyan sandstone are analyzed. Based on the sensitivity law of brittleness index of cyan sandstone to confining pressure, a brittle exponential evolution model with brittleness degradation factor ? and lithology characteristic ? as parameters is established. Test data is verified by the same functional model. The results show that the brittleness of the cyan sandstone weakens with the increase of confining pressure and the rate of change of brittleness index shows strong sensitivity to confining pressure. The larger the confining pressure, the smaller the decay rate of the rock brittleness index under the same freeze-thaw cycles. Under the same confining pressure condition, the brittleness of the blue sandstone decreases with the increase of the number of freeze-thaw cycles, and the effect of brittleness degradation caused by unit freeze-thaw cycles increases with the number of freeze-thaw cycles. The brittleness exponential evolution model has a good correlation with the fitting data of freeze-thawed cyan sandstone, black sandstone and marble, and the parameters ? and ? accurately reflect the brittle evolution characteristics of different freeze-thaw cycles and different rocks.

Based on the one-dimensional consolidation theory of unsaturated soil developed by Fredlund, the consolidation equations under two-dimensional plane strain are established, and the analytical solution of single-layer unsaturated soil under plane strain is obtained. Based on relevant theories, it is assumed that the volume change and the permeability coefficients are both constant, and the second-order binary partial differential equations are established, considering uniform or linear distribution of initial super-porosity pressure along the depth of the soil under the condition of instantaneous loading. To solve the equations, we first introduce the function method to reduce the order of the equation, and then obtain the general solution of the equation by variable separation method. Based on the solution, a case of two-dimensional plane strain problem under single-sided drainage conditions is investigated, and the correctness of the method is verified by numerical solution. The isochronal line of excess pore water and gas pressures dissipated in the vertical and horizontal directions in the two-dimensional plane is calculated by the proposed method. The influence of initial excess pore pressure on the consolidation and dissipation processes under different linear distributions is analyzed by calculation and comparison. The results show that the different distribution of initial excess pore pressure has an almost negligible effect on the dissipation of excess pore gas pressure, and has a great influence on the dissipation of excess pore water pressure.

Aiming at the consolidation of foundation with the horizontal sand blankets, a two-dimensional consolidation model under ramp loading was established, and the corresponding semi-analytical solution was obtained using boundary transform method. Based on this solution, the effects of geometric and physical parameters of sand blankets and ground soil on the consolidation subjected to ramp loading was analyzed. The results show that the consolidation rate increases with the increase of horizontal permeability coefficient but decreases with the increase of foundation width for the soil. For sand blankets, the consolidation rate increases with the increase of sand blankets thickness and horizontal permeability coefficient. In addition, for the external loads, the faster the loading rate, the shorter the time required for the pore pressure to reach the peak value, and the higher the consolidation rate of the foundation. Lastly, the influence of horizontal permeability coefficient and thickness on the permeability of the sand blankets was considered comprehensively. When the boundary condition of the interface of sand blanket and soil foundation is close to the full drainage boundary condition, the parameter needs to be greater than 200 ( is the thickness of the sand blankets, and is the horizontal permeability coefficient of the sand blankets, is the width of soil foundation, and is the vertical permeability coefficient of soil foundation).

A perfect anisotropic permeability model is helpful to guide the drainage and grouting scheme of underground buildings during construction and operation period. To study permeability anisotropy model, mixed kaolinite-montmorillonite clays were used in a series of permeation experiments by triaxial permeameter, and the development of anisotropic permeability model was attempted from both macroscopic and microscopic perspectives. The results show that: as the amount of bentonite increases, the small pores increase, but the large pores decrease; as the consolidation stress increases, all pores decrease, and the maximum pore size decreases. Macroscopically there is no correlation between the void ratio considering the liquid limit void ratio and the permeability anisotropic ratio, which indicates that the void ratio e and liquid limit void ratio are not the key parameter determining the permeability anisotropy ratio. The permeability anisotropy model expressed by microscopic parameters indicates that it is not only feasible to explore the permeability anisotropy model from the microscopic point, but also to reveal the essence of permeability anisotropy. In all microscopic models, the permeability anisotropy model expressed by pore index - is well correlated, which can reflect changes in larger pores.

Interlayer insertion and interlock will be formed when the pebbles-filled soilbags are stacked vertically and staggered, which will affect the shearing strength and failure modes of the stacked soilbags. A series of shear tests on stacked soilbags filled with pebbles was conducted to show that the interlayer insertion and interlock can strengthen the shear strength of the stacked pebbles- filled soilbags. The insertion increases as the applied normal stress increases while the interlock decreases slightly. There are two shearing failure modes of the stacked pebbles-filled soilbags during the shearing including deformation failure of filling materials (occurs first), and followed by interlayer sliding failure. For the five layers of staggered arranged pebbles-filled soilbags, deformation of stacked soilbags will also happen before the interlayer sliding. The sliding surface of staggered arranged soilbags is ladder-like due to the interlayer insertion. Additionally, the interlayer friction resistance of the five layers of soilbags filled with pebbles is found to be related to the shape of the sliding surface.

A series of undrained, partially drained and completely drained triaxial tests were carried out to investigate the influence of drainage boundary conditions on the strength characteristics of saturated clay. The partially drained tests were carried out by controlling the strain increment ratio of the volume and axial strains. The tests investigated the influence of drainage boundary conditions on the mechanical properties of saturated clay including the pore water pressure, the effective stress path and the asymptotic behavior of the p-q plane. Based on the asymptotic state and dilatancy characteristics, an asymptotic state constitutive model for saturated clay was established by introducing the strain increment ratio into the stress path constitutive model. The comparison between experimental results of pore water pressure and effective stress path and simulations demonstrates a good predictive ability of the model. The test results show that the strain increment ratio of saturated clay should be less than 0.3. The drainage condition affects the dilatancy of normal consolidated clay, the effective stress path and the shear strength of soil. With the increase of the strain increment ratio, the pore water pressure and the effective stress ratio of saturated clay decrease but the strength increases. The saturated clay specimen will be in a critical state for a long time, and the change in drainage conditions can inhibit or accelerate the failure of the soil.

To study yield characteristics of unsaturated loess in the effective stress space, a series of undrained isotropic net stress compression consolidation and shear tests with different intermediate principal stress parameters b is conducted on unsaturated intact loess by using true triaxial apparatus. The effective stress yielding behaviors of unsaturated loess under true triaxial compression conditions are studied. The results show that the effective stress ratio decreases with an increase in intermediate principal stress or net confining pressure, and the effect of intermediate principal stress on effective spherical stress is greater than that of generalized shear stress. The yield curves determined by the effective stress ratio-volume strain curves have good regularity in the effective stress space, the effective yield stress at yield point increases with an increase in intermediate principal stress and initial suction. The effective stress yield strength surfaces and the strength failure surfaces on the π plane are in good agreement with the SMP strength criterion. As the effective spherical stress and initial suction are larger, the yield strength surface and strength failure surface are more larger. The equations of elastic shear strain and plastic shear strain under true triaxial conditions are proposed. By analyzing the relationship between effective stress and plastic strain, it is concluded that the plastic potential surfaces on different meridian planes in the effective stress space are elliptical, and the elliptical yield surface increases with an increase in intermediate principal stress.

Due to the enrichment of a soluble salts and various metal cation components in seawater, seawater slurry shows large specific gravity, low colloidal rate, poor stability and high water loss, and does not meet the requirements of slurry shield construction. In order to modify the seawater slurry to maintain the stability of the excavation surface and reduce the construction cost of the shield tunnel, eight additives, such as CMC, cellulose PAC, and ammonium polyacrylate, etc., were used to test the properties of seawater slurry. The additives which modified the seawater were selected, and the influence law of the additives amount and time on the properties of the seawater slurry was analyzed. At the same time, the modified seawater slurry formation penetration test was carried out based on the preferred additive CMC using a mud film formation test platform. Results show that different additives have significant differences in the properties of seawater slurry. The cellulose PAC and CMC have better modification effect on seawater slurry. The turbid layer, mixed layer and flocculated sediment layer appear in 24 h. The amount of water filtered by the seawater slurry to the formation is greater than that of the modified seawater slurry, and the slurry skin is slightly thicker, but it is sparse. It can be speculated that the additive neutralizes part of the seawater component and flocculates and precipitates, and the excess additive exhibits a thickening effect on the pale cement slurry.

To study the effect of freeze-thaw on the shear creep characteristics of engineering rocks in cold regions, the granite samples from Huibai tunnel in Jilin province were taken as the research object, and the microscopic characteristics and shear creep tests of samples under different freeze-thaw cycles were carried out. The results show that: 1) With the increase of freeze-thaw cycles, the cracks and voids in the samples develop continuously, and the damage of rock surface becomes more and more obvious. 2) The pores in the sample are mainly composed of small and medium pores, and the porosity increases nonlinearly with the increase of freeze-thaw cycles. 3) With the increase of freeze-thaw cycles, creep deformation and creep rate increase gradually, while creep time, failure stress and long-term strength decrease obviously. According to the test results, expressions of unsteady creep parameters of freeze-thaw rocks are established, the damage viscous element of freeze-thaw rock is proposed, and the freeze-thaw shear creep constitutive model of granite is constructed. By comparing creep test curve with theoretical model fitting curve, the correctness and applicability of the model are verified. Through sensitivity analysis of creep parameters, the influence of creep parameters on granite creep deformation is studied, and the variation law of creep parameters with the number of freeze-thaw cycles is given. The research results have guiding significance for long-term stability evaluation of rock mass engineering in cold regions

The seepage stability of high earth rockfill dam greatly depends on the protection of filter layer on core-wall material. Under impounding and long-term running conditions, the core wall undergoes complex structural load, saturation and water effects. Being affected by differential settlement, complex structural stress, hydraulic fracturing and seepage flow, the core wall when cracks formed will meet severe situations for seepage stability and filter layer of protection. To solve above problems, reverse filtration tests on unconventional filling material and slurry were designed to simulate the scouring and blocking of the particles under the cracking of the core wall by the reverse filter material and the deposition process in the crack. The results show that core wall particles are intercepted and deposited on the upstream surface of the filter layer. The filter material can effectively prevent the loss of clay particles. When the core-wall material and the filter material meet the filter criterion, the filter layer can still effectively protect the core-wall material under extreme conditions.

In this paper, the loading wet yield surface (LC yield surface) in the SFG model and the suction increasing yield surface (SI yield surface) proposed in the BBM model are unified into a single smooth yield surface. The corresponding elasto-plastic constitutive model is derived under the framework of elasto-plastic theory. The model calculation parameters of Jiangxi red clay were determined by unsaturated consolidation direct shear test. The calculation parameters are entered into the model program and the stress path of the unsaturated triaxial test is calculated by the program and compared against experimental results in a published paper. Based on stress-strain curves calculated from the comparison model and test results, we draw a conclusion that the calculation results of the unsaturated triaxial test model under different stress paths are in good agreement with the experimental results. It is verified that the model can better simulate the volumetric strain behavior of unsaturated soil under various stress paths than other models. Uniform yield surface simplifies the coupling analysis between loading wet yield surface and suction increasing yield surface. Our model solves the problem of inconvenience caused by the discontinuity of the double yield surface, and broadens the applicability of the SFG model.

Loading pattern and stress path have great influences on liquefaction resistance of saturated sand. Using GDS hollow cylinder torsion shear apparatus, a series of undrained cyclic loading tests was performed under complex loading conditions on isotropic consolidated saturated coral sand in a Nansha Island, South China Sea. The influence of the inclination angle of principal stress ( ) on liquefaction resistance of coral sand was discussed under 90° jump rotation of principal stress path. It is found that: when the cyclic stress ratio (CSR) is used as the stress level index, has no significant effect on the liquefaction resistance of coral sand as the change in intermediate principal stress coefficient (b) is not controlled; when b always maintains at 0.5, the liquefaction resistance of coral sand shows a tendency to decrease first and then increase with the increase of , and the liquefaction resistance is the lowest when 45°. Based on analyzing the change of the major and minor cyclic principal stresses and caused by complex cyclic loading, a unit cyclic stress ratio (USR) as a new index is defined for cyclic resistance of coral sand. A virtually unique correlation between USR and Nf can be established under different cyclic loading patterns and stress paths considered. The recompiled original experimental data of four types of cohesionless soils in the published literature independently verified the general applicability of USR to characterize liquefaction resistance.

The creep behaviors of saturated saline soil are studied in the consolidation creep test under isothermal conditions in this paper. Based on the element model, the fractional creep model of saturated saline soil was established by introducing Abel dashpot and osmotic suction. The phenomenological correlation between salt content and creep behavior of saturated saline soil is discussed. The effects of osmotic suction on the ratio of the secondary compression coefficient to the compression index, initial shear modulus and initial shear strain are analyzed by combining experimental results with fractional model fitting. The fractional order model is fitted by the test results of different stress levels and salt content. The validity of the model is verified by the viscosity coefficient formula. The results show that the ratio increases exponentially as the osmotic suction increases. The initial shear modulus decreases as the osmotic suction increases, and the initial shear strain exhibits a linear relationship with the osmotic suction. Comparing with the integer element model, the fractional creep model proposed in this paper is more suitable for predicting the creep behavior of saturated saline soil. Combined with the results of experiments and model analysis, it is found that the increase of salt content promotes the creep behavior of saline soil.

The constitutive model of unsaturated soil under dynamic loading is helpful to solve related engineering problems. In the framework of plastic incremental flow theory, by combining Barcelona basic model (BBM) with the plastic hardening criterion proposed by one of the authors and considering the cyclic loading with the controlled matric suction, an elastoplastic two-surface model is established for describing unsaturated cohesive soil. Combined with the concept of memory centre, a bounding surface and a geometrically similar loading surface describe the nonlinear, cyclic plasticity and deformation accumulation characteristics of unsaturated soil when the stress path periodically changes the loading direction jointly. Dynamic triaxial shear tests were conducted to determine dynamic mechanical properties of unsaturated clay silt, which analyses the influences of matric suction, net cell confining pressure and dynamic stress amplitude on cyclic plasticity. Experimental results of the unsaturated soil under static and dynamic loading are compared with the correlative model predictions, which shows a good agreement. It indicates that the elastoplastic two-surface model can simulate the mechanical behaviour of unsaturated soil under cyclic loading with controlled matric suction.

To investigate the swelling and softening characteristics of expansive rocks, swelling test and conventional triaxial test were carried out. The scanning electron microscopy (SEM) and nitrogen adsorption (NA) techniques were conducted before and after soaking water. Undisturbed expansive rock samples were selected to fully consider the cementation among the particles inside the expansive rock and original structure. Experimental results show that the expansion has apparent anisotropy and the axial expansion is 1.5 times of the radial one. With the increase of relative water content, the peak strength decreases rapidly and then slowly decreases, the elastic modulus and cohesion decrease. Under the condition that the confining pressure remains unchanged, the deformation form of the expansive rock changes from tensile failure, tensile-shear failure to shear failure, and surface cracks increase when the expansion rock fails. SEM results show that the microcracks of the expansive rock increases after the water soaking, and the pore development is obvious, which is the softening fundamental of the expansive rock.

The dynamic field response to earthquake in the coral sand is affected by its special engineering properties. In order to reveal the seismic response characteristics of the pile-soil-superstructure in the coral sand site, the shaking table tests of pile groups with three-storey frame structure in coral sand under different earthquake intensities are carried out. The dynamic responses to soil and structure are analyzed and compared with those in the liquefied quartz sand of Fujian. The results show that the excess pore water pressure ratios in both coral and quartz sands are far less than 1 under 0.1g seismic intensity, demonstrating that no liquefaction occurs in both sites. However, both coral and quartz sands are liquefied under 0.2g seismic intensity, and the liquefaction degree of coral sand is less than that of quartz sand. Compared with the quartz sand site, the coral sand site still has some shear strength and stiffness after the liquefaction. The settlement, horizontal displacement and column bending moment of coral sand site under 0.1g and 0.2g seismic intensities are smaller than those of quartz sand site. The position of peak bending moment of pile foundation under different seismic intensities is not the same.

In order to study the confining pressure effect and particle size effect of shear properties of calcareous sand, triaxial shear tests were carried out under different particle sizes, relative densities and confining pressures. The stress relative softening coefficient and dilatancy coefficient were introduced to quantitatively characterize the strain softening and dilatancy characteristics. The experimental results show that with the increase of confining pressure, the strain softening and dilatancy characteristics of calcareous sand samples with different particle sizes decrease gradually, and the confining pressure is semi-logarithmic linear with the relative stress softening coefficient and dilatancy coefficient. The strain softening and dilatancy characteristics of calcareous sand samples with different particle sizes disappear due to the existence of critical confining pressure of strength and critical confining pressure of volume variation. In the range of particle size 5-0.075 mm, confining pressure has a significant effect on softening and dilatancy characteristics of loose samples, but there is no significant correlation with particle size. For dense samples, the effect of confining pressure on softening characteristics of samples increases with decreasing particle size, while the effect on dilatancy characteristics of samples decreases. Under a low confining pressure (50 kPa), the breakage of 0.5-0.25 mm particle size group is the most significant.

Grain size distribution, grain shape, and filling density are the critical factors that affect the pore structure and permeability of coarse-grained soil. However, only a few studies have examined the effect of grain shape on the permeability of coarse-grained soil. The main reasons are that it is not easy to quantitatively describe the grain shape and to study its influences on pore system characteristics. This study compares the pore system characteristics and permeability of samples filled with irregular gravels, spherical and regular octahedral grains, respectively. The grain shape was quantified by the length-width ratio and roundness obtained in the previous study. The images of internal structure for samples were obtained by the computed tomography (CT) scanning, and then the specific surface area was obtained for reconstructed three-dimensional (3D) pore structure of samples. The results indicate that the specific surface area is a reliable parameter to identify the pore structure characteristics of coarse-grained soil. For samples with the same grain size distribution and porosity, the specific surface area of the pore system decreases as grain roundness increases and grain shape approaches sphere. The hydraulic conductivity results show that for these samples, the hydraulic conductivity increases with the increase of grain roundness but the decrease of the specific surface area of pore system. The samples filled with spherical grains have the highest permeability. The samples filled with the more nonspherical grains contain pore systems with more resistance to seepage flow and are less permeable.

A series of undrained strain-controlled cyclic triaxial tests was conducted on saturated Nansha coral sand. The properties of initial maximum shear modulus, of coral sand and the degradation properties of the maximum shear modulus, of coral sand during the cyclic loading were analyzed. The of coral sand is greater than that of terrigenous sands. Compared with terrigenous sands, the effective confining pressure, has stronger influence on the of coral sand. The difference between the values of coral sand and terrigenous sands is due to the irregular shapes and the inner pore of the coral sand grains. The of coral sand is determined by the slopes of the hysteresis loop at the stress reversal points. The degradation of the maximum shear modulus during the cyclic loading is caused by the increasing excess pore pressure and the structure damage of coral sand. The of coral sand decreases faster than that of terrigenous sands with the increasing excess pore pressure ratio, . The existing models for the prediction of of terrigenous sand were established by the relationship between and , and it is not applicable to coral sand. Based on the elastic strain energy theory, a new damage parameter, is introduced to research the relationship between / and of coral sand. Finally, a new prediction model of coral sand was proposed.

Plenty of high-fill slopes need to be strengthened in engineering projects in the mountainous area of the northwestern district of China with complex geological conditions. To provide sufficient anchoring force to fill slopes and to ensure their stabilities, we put forward a new structure of safety, stability, economy and convenience, named frame with prestressed anchor-plates, which suits for reinforcing the slopes with large fill, and whose reinforcement effect is great. Based on the limit equilibrium theory, we proposed the formula for pull-out resistance and the checking calculation method for the stability. Finite element analysis software PLAXIS 3D was applied to compare and verify the results of the proposed method. The displacement of the slope and the internal forces of a column in the frame are further analysed, which explains the rationality of the results of numerical simulation, and proves that the frame with prestressed anchor-plates is effective for strengthening the slope and limiting the displacement by comparing with the displacement data of a slope project. By analysing the variation of axial force and frictional strength during the process of construction, the working mechanism between the plates and the soil is exposed, and the influence of the prestress on the structure is explored. The analysis results guide the design of high-fill slopes strengthened by the frame with prestressed anchor-plates.

The exploitation of coal resources in China is seriously threatened by water hazards. A coupled hydromechanical modeling of mining above a confined aquifer with FLAC3D was carried out to numerically investigate the fractured behavior of inclined floor and water outburst risk. Based on the double-end plugging leak detection device, the in-situ testing of mining-induced damage depth was implemented. Furthermore, the mechanical model of inclined water-resisting key strata was constructed to theoretically calculate the stability of inclined floor under the synergistic action of the roof caving rock mass, floor mining-disturbed rock mass and non-uniformly distributed confined aquifer. Results show that obvious three-zone failure characteristics in an asymmetric state are formed in the inclined floor after excavation. The mining failure zones along the strike and inclination are approximately spoon-shaped and upper small and lower large inverted saddle-shaped, respectively, and the maximum failure depth of numerical simulation with 16.71 m is approximately equivalent to the measured result of 15.49 m. The theoretical calculation shows that the pre-failures of inclined water-resisting key strata are not located in the middle of its boundary, but occur near the normal intersection points between the curves passing through the maximum deflection position and the right or lower boundary. The pre-failure areas may intersect with each other along the boundary, and gradually extend to the whole inner region of the aquifer. The water inrush location and risk of inclined water-resisting key strata calculated by the theoretical model are in good agreement with that of numerical simulation. The research results in this paper can provide some theoretical guidance and reference for the evaluation and safety control of floor water inrush under mining with pressure.

In order to study the influence of excavation near shield tunnels on the force of tunnel segments, the mechanism of surrounding pressure change on tunnels caused by nearby excavation is studied. A model of additional confining pressure redistribution is proposed which can describe the process of force-displacement-rebalancing of tunnels, and the calculation formula of additional confining pressure is deduced. The internal force of lining under the corresponding confining pressure is calculated by using the modified routine method. The influence of foundation pit excavation on the confining pressure and internal force of shield tunnels is studied based on the analysis of a practical engineering example, and the influencing factors are analyzed. The analysis results show that confining pressure of the tunnel before excavation presents a "bell shape" distribution. After excavation, the confining pressure on both sides of the tunnel decreases, and the confining pressure on the excavation side decreases more. The excavation of the foundation pit increases the positive and negative bending moments and the positive and negative shear forces of the nearby tunnel, and decreases the axial forces of the arch top and the arch bottom. With the increase of the stress release coefficient of the side wall of the foundation pit, both the absolute values of the additional confining pressure and of the additional bending moment will increase, and the response of bending moment to unloading of foundation pit excavation is more obvious. Shallow shield tunnel is more sensitive to the influence of the excavation of side foundation pit, and the influence of excavation of side foundation pit will decrease obviously when the burial depth of the tunnel is greater than that of the foundation pit excavation. With the increase of the distance between the foundation pit and the nearby tunnel, the influence of the foundation pit excavation on the tunnel will also be reduced.

The standard formula for calculating the soil shear strength of the preloading ground under anisotropic consolidation is not applicable to isotropic consolidation process. In this paper, a new formula was proposed to calculate the soil shear strength of the preloading ground under isotropic consolidation process. This new formula was derived by analyzing the calculation principle of the two existing fundamental methods, which are effective stress method (ESM) and effective consolidation stress method (ECSM), respectively. Then the results that calculated by the new formula and the standard formula applied to vacuum preloading and vacuum combined surcharge preloading were theoretically discussed and compared. Finally, the applicability of the new formula and the standard formula were tested by the practical engineering, and the difference between the calculated strength and the measured strength were also analyzed. The results show that the ECSM can be applied to the preloading ground under both the isotropic consolidation and the anisotropic consolidation, while standard formula is only applicable to surcharge preloading ground theoretically. The values of soil shear strength of the vacuum preloading and vacuum combined surcharge preloading that calculated by the standard formula are smaller than those calculated by the new formula. The relative difference of the two calculation values only relates to the friction angle and increases as the friction angle increases. In the vacuum combined surcharge preloading treatment project, the shear strength prediction values by the new formulas are closer to the measured values than those by the standard formulas. The result of this study can be potentially helpful for calculating different kinds of preloading grounds in practice.

According to the physical and mechanical properties of foundation soil in the area of deep multilayer soft soil, a new pile-side and pile-end model is adopted to simulate the load transfer mechanism of a single pile by considering the initial ultimate shear stress of pile-side soil at low-load level, the stress softening characteristics at high-load level and the piecewise performance characteristics of pile-end soil bearing capacity. Based on the above model, the iterative method can be applied to calculate the settlement of the single pile top, the axial force of the pile body and the pile side resistance. The p-y curve, which is easy to obtain and suitable for soft soil, is used to describe the nonlinear relationship between pile-soil interface force and displacement. Based on the Euler-Bernoulli beam and centre difference theory, a numerical calculation method is conducted by considering the boundary conditions of the pile tip. The rotation angle, shear force and bending moment of the pile along the length direction are calculated to obtain the variation characteristics of these variables under a specific load. Finally, as verified by an engineering case, the calculation of the above method is simple and in good agreement with the actual testing results.

The pile-soil stress ratio is an important parameter for calculating the bearing capacity and settlement of the pile-net composite foundation, which is related to the consolidation settlement of the foundation and has obvious time-varying characteristics. The calculation theory of loosening earth pressure based on Terzarghi soil arch model is discussed on the assumption that the soil of sliding surface reaches limit state, and it is not suitable for the calculation of pile-soil stress under the condition of small deformation of pile-net foundation. Therefore, on the basis of Terzarghi model, the equivalent stiffness ideal elastic-plastic model is adopted for the transfer function of relative displacement surface, and the theoretical solutions of pile-soil stress and soil arch height are derived by combining the equilibrium equation of soil element with the deformation coordination equation. The quantitative variation of pile-soil stress and the membrane effect with each design parameter is analyzed systematically. The results show that the improved method is more applicable than the existing arching algorithm model. With the increase of pile-soil differential settlement, the arching height and pile-soil stress ratio gradually increased, and the arching ratio decreased in hyperbolic shape, while the membrane effect works gradually. The arching effect is significantly weakened by increasing the filling load, and the pile-soil stress ratio decreases with the increase of pile spacing and increases with the increase of cohesive force. Based on the improved method and the field measured data, the time-varying characteristics of pile-soil stress are analyzed, and the rationality of the method is verified. The method proposed can be used as a reference for the calculation of pile-soil stress on the pile-netted foundation.

Developing the constitutive models of unsaturated soils is a main field of soil mechanics. Although a large number of approaches have been applied, only a few were reported to consider the explicit integration algorithms in FEM. In this paper, we consider the numerical explicit integration with sub-stepping error control implementation of an extended Cam-clay constitutive model for unsaturated soils in ABAQUS umat (user-defined material model) subroutine. The modified Euler method has been used to solve the ordinary differential equations associated with both of the saturation and the saturation increment obtained by usdfld subroutine from ABAQUS. The accuracy, stability and robustness of the schemes were examined by a set of triaxial compression tests between the modified Cam-clay model from ABAQUS and the extend Cam-clay unsaturated model. As a conclusion, the extended Cam-clay unsaturated model with the explicit integration scheme shows great performance in a series of stress pass numerical triaxial test. Finally, the new unsaturated soil umat was applied to analyze the dry-wet cycle triaxial consolidation tests with hydraulic hysteresis. The results show the material parameter b plays a significant role for accumulative irreversible volumetric strain in dry-wet cycle condition, in which the accumulative strain decreases as b reduces but rises with b increases. Those results provide a solid foundation for further studies.

Upper bound adaptive finite element method based on the six-node triangular high-order element has the advantages of high calculation accuracy and the ability to directly obtain structural failure mechanism from the refined mesh of the computational domain. However, if the linearization method of yield criterion is still used to establish the upper-bound finite element model, the calculation efficiency will be lower. Therefore, based on the previous research, a second-order cone programming method with higher computational efficiency is introduced to improve the computational efficiency of the upper bound finite element method. Upper bound adaptive finite element method based on second-order cone programming and the higher-order element is established. The analyses of slope stability and bearing capacity of strip foundation show that the proposed method improves the calculation efficiency of the upper bound finite element method, and the refined mesh of the computational domain can directly obtain the refine failure mechanism. It is also shown that the calculation time of the proposed method is significantly shorter than that of the linearization method of yield criterion under the same accuracy. Some examples are given in this paper to show the accuracy and effectiveness of the proposed method. This study can provide some references for theoretical research and engineering practice.

A detailed introduction to a modified symmetric and anti-symmetric decomposition (MSAD) based three-dimensional numerical manifold method (3D NMM) is given, and a formula to select the penalty factor of penalty method in 3D NMM is proposed. In the MSAD-based 3D NMM, a Bathe implicit time integration scheme is introduced, an ideal plastic constitutive model with the unified strength theory and non-associated flow rule is developed, and a simulation of a 3D elastic-plastic excavation problem is conducted. The MSAD-based 3D NMM is used to study nonlinear dynamics. The results show that: The Bathe implicit time integration scheme and the MSAD-based 3D NMM are able to ensure the stability of the simulation results for nonlinear dynamics problems with large rotation and long-time duration, and to maintain the conservation of kinetic energy and angular momentum for the conservative system. The MSAD theory is double-verified, in the simulation of large rotation problems, showing that it has good stability and high computational precision, and it is able to reasonably separate the rotation and strain apart from the incremental deformation gradient, and accurately update the rotational stress without causing the problem of false volume expansion.

Prestressed anchor cable reinforcement is an important way to improve slope stability. Understanding the mechanism of reinforcement of slope by prestressed anchor cables is of great theoretical significance for guiding the design of slope reinforcement. Based on the calculation model of the high and steep slope, through continuously improving the strength reduction coefficient of rock and soil mass, we obtained the variation law of the displacement of slope foot and internal force of prestressed anchor cables. According to the stress distribution law of rock mass reinforced by prestressed anchor cables, some useful conclusions are drawn. When the strength reduction coefficient of rock and soil mass exceeds the safety factor of the slope, the internal force of prestressed anchor cables increases rapidly. The internal force is obvious when it is close to the foot of the slope. The change of internal force of anchor cables at the foot of slope can be monitored for evaluating the stability. For high and steep slopes, most of the prestressed anchor cables can not improve the compressive stress on the potential sliding surface and the shear strength of the sliding surface. The primary mechanism of the prestressed anchor cables to reinforce high and steep slopes is to control the displacement of the potential sliding body of the slope.

The coupling performance of embedded optical fiber and tunnel lining is studied using theoretical and experimental methods, and then is verified in practical engineering. We calculate the strain transmission efficiency of fiber by modeling and analyzing the structure of optical fiber, intermediate and matrix. Totally two sets of experiments are designed. The reinforced concrete beams with 6 kinds of optical fiber layout are designed in same working condition. The multistage loading was carried out at a single point in the way of displacement control. At the same time, 6 optical fibers are monitored based on the BOFDA (Brillouin optical frequency domain analysis) technology. The results of two different groups show the similar law: six optical fibers can effectively monitor the process of beam loading from the stage of beginning to the stage of yielding, and the coupling between fiber and beam is good in this process. When the reinforcement begins to yield to the failure process, the fiber strain no longer increases, even decreases or presents the state of fiber fracture, and the coupling of the fiber and the beam is poor in this process. Except for the slotted embedded fiber, the effective monitoring strain difference is 3 000×10?6, the effective strain difference of the remaining fiber is 2 000×10?6. Under the condition of long distance (>>146 mm) embedding, the strain transmission efficiency of optical fiber is close to 100%. Taking the underground excavation section of the new built airport in Beijing as an example, the fiber is embedded in the two waist and vault of the initial lining, and the construction process of the CRD method is monitored by monitoring fiber. Monitoring results show that the embedding technology is feasible, which is able to provide references and valued suggestions for other related monitoring projects.