Cement-based 3D printing technology is increasingly popularized in civil construction and rock-like physical simulation, yet its cement-based 3D printing materials not only is limited by the challenges in quality control such as liquidity, shrinkage, and processability, but also is lack in basic formula in concrete material. This paper firstly establishes a set of assessing system based on six indexes and corresponding quality classification method considering the whole process of solid model forming for cement-based 3D printing, including fluidity, extrusion, setting time, buildability, compactness and deformation rate. The quality evaluation of the 3D printing solid model is realized in three aspects: printing process, stacking process, and solid accuracy. Then, through the two-stage orthogonal design and printing test with different threshold ranges, the basic mix ratio of cement-based 3D printing materials, which is ideal in comprehensive printing performance, is obtained. Finally, the uniaxial compression test is carried out for the printed cement-based 3D solid model and its rock-like mechanical properties are evaluated, which can provide a new type of rock-like cement-based 3D printing material. The specific mix ratios lay the foundation for the civil construction and physical simulation test of rock engineering based on cement-based materials.

The stimulation of thermal reservoir in sandstone and long-term stability evaluation are of great significance to the development of geothermal energy. The mechanical properties of fractured sandstone under 0－8 thermal shocks are studied in this paper. The experimental results show that the P-wave velocity, uniaxial compressive strength and elastic modulus of the fractured sandstone all decrease gradually with the increase of the number of thermal shocks under two types of cooling methods. Compared with cooling method in water, the natural cooling method in air has less damage to mechanical properties of fractured sandstone. The uniaxial compressive strength and elastic modulus of fractured sandstone show a good exponential function relationship with the number of thermal shocks. Both the P-wave velocity and the elastic modulus can be used to describe the damage of the fractured sandstone with the number of thermal shocks. The first thermal shock weakens the mechanical properties of fractured sandstone most severely, and the deterioration effect of mechanical properties is significantly slowed down when the number of thermal shocks exceeds 4. In addition, the uniaxial compressive strength and elastic modulus of fractured sandstone also have a good exponential function relationship with the P-wave velocity. Finally, the thermal shock process of sandstone samples is simulated in COMSOL Multiphysics, and the effects of heat transfer coefficient and prefabricated cracks on the internal temperature field and stress field of sandstone are discussed, revealing the mechanism of thermal cracking in sandstone under thermal shock effect.

Salt rock has been recognized as an ideal medium for energy storage or oil and gas storage because of its good creep characteristics and self-healing. Accurate characterization and prediction of the complex mechanical behaviour of salt rock is the basis for ensuring the safety of the underground space utilization project of salt caverns. Based on proposed parameters of hardening and other characteristic factors, in this study, a new creep fatigue constitutive model is developed for salt rock considering complex loading and unloading path. Based on the dislocation mechanism of salt rock deformation, hyperbolic damping elements are introduced as state variables to characterize the degree of rock hardening. The influence of loading and unloading history on the deformation behavior of salt rock is considered according to the evolution of hardening parameters. Based on the stress-strain relation of the classical Norton model, a basic mathematical relation is established for the creep fatigue constitutive model. By assuming the initial nucleation length and considering the material fracture toughness, the stress-strain relation is modified for the range of adjacent failure stage (accelerated deformation stage) based on a newly introduced crack growth factor. In this manner, the proposed model can well predict the plastic deformation characteristics under complex loading and unloading paths such as conventional creep, cyclic loading and unloading, lower limit interval cyclic loading and unloading, trapezoidal wave creep cyclic loading and unloading. The model can also better characterize the interaction between constant load creep and cyclic loading and unloading. Most of the model parameters have clear physical meanings in the new developed creep fatigue constitutive model. Parameter a represents the relation factor between stress and deformation rate in the steady-state deformation stage of salt rock, parameter b determines the relation factor in the first stage of deceleration deformation stage of salt rock, and parameters of  d₀  and μ_d  represent the initial crack nucleation amount and crack growth rate factor, respectively. The  d₀ and μ_d   jointly affect / modify the stress-strain relation at the critical failure stage of the model.

The deformation and failure evolution process of rock slope during disaster incubation period is controlled by internal long fissures (controlling fissures), and the evolution mechanism is of great significance for the prevention of landslide disasters. Based on the transparent physical model experiment technology, two typical rock slopes with controlling fissures (one with a steep fissure at the back and the other with a gently inclined fissure at the front) were selected as the objects, and the evolution process of deformation and failure inside the slopes was studied through physical model experiments using the self-developed equipment. The displacement rate and strain rate were taken as the characterization quantities of the deformation and fissure propagation, and the spatiotemporal evolution mechanism under the influence of fissures was analyzed with the reference of the common slope without controlling fissure. The conclusions are: (1) The reliability of the proposed experiment method in the study of the deformation and failure evolution process inside the slopes was verified through the simulation of internal deformation accumulation and progressive process of fissure initiation, propagation, and penetration. (2) The deformation and failure process of the slopes with controlling fissures is similar to that of the slope without controlling fissures and can be divided into four stages: deformation accumulation, failure band/fissure initiation, failure band/fissure expansion adjustment, and rapid expansion and penetration of failure bands/fissures. (3) The tip of steep fissure at the back undergoes a tensile-shear mixed initiation and expands downward due to the pushing action induced by initial fissure slip deformation, while the tip of gently inclined fissure at the front undergoes tensile initiation and expands upward due to the traction induced by initial fissure slip deformation. The propagation rates of fissures increase exponentially with the increasing length of fissures. (4) The fissure propagation modes change with the evolution of slope deformation and fissure propagation. The steep fissure at the back starts to propagate in tensile-shear mixed mode and turns to propagate in shear mode, and finally shears out near the slope toe. The gently inclined fissure at the front firstly propagates in tensile mode and then transforms to shear mode, and finally intersects with the failure zone at the back.

The longitudinal equivalent bending stiffness (LEBS) of the shield tunnel is a key parameter when the longitudinal structural analyses of the shield tunnel are conducted by the equivalent continuous model. There will be a significantly nonlinear characteristics on the LBSE if the longitudinal axial force and the bending moment are loaded simultaneously. In this paper, based on the existing theories of the nonlinear bending stiffness of the shield tunnel, a calculation model of the longitudinal nonlinear equivalent bending stiffness of the shield tunnel incorporating its transverse performance has been proposed where the transverse deformation characteristics are considered. The LEBSs of the shield tunnel are derived strictly based on the elliptical integral when the circumferential joint of the shield is closed completely, semi open, and open fully respectively due to the coupling action of the longitudinal axial force and bending moment. The criteria of the critical axial force and the critical bending moment to distinguish the three bending modes are deduced with the equations about the neutral axial position. Then the reliability of the proposed model is validated via the results calculated by the existing analytical model, the model test data and the numerical results. After that, the analyses of the influences of the transverse performance of the shield tunnel on its longitudinal stiffness are carried out using the verified model when the shield tunnel suffers the coupling action of the longitudinal axial force and bending moment. Finally, the calculation errors of the simplified deductions are discussed. In addition, a coupled analysis method for the transverse and longitudinal deformations of a shield tunnel induced by additional load is developed based on the established analytical model. The results show that the analytical derivations of the proposed model are accurate and reliable. The LEBS of the shield tunnel is closely related to its transverse stiffness, and there is a positive correlation between the two. The LEBS of the shield tunnel is improved dramatically with the increase of the transverse bending stiffness if there is a compressive-bending state. The matching relationship between the longitudinal and transverse stiffnesses of the shield tunnel subjected to the coupling actions of the longitudinal axial force and bending moment is established with the proposed model, and a bridge to implement the longitudinal and transverse coupling analyses on the structures of the shield tunnel is also built by the proposed model.

Coral sands are commonly used in hydraulic fill foundations and as subgrade fill in the construction of islands and reefs. The stress paths followed by soil consolidation or filled subgrade are characterized by K0 consolidation or constant stress ratio path. It is necessary to develop a computational model that reflects the effect of stress path on deformation in order to accurately estimate soil deformation during the filling process. Based on the generalized Hooke's law, a nonlinear elastic model in the form of a power function is proposed to describe the stress-strain curve of coral sand, and the functional expression is given. A series of K0 consolidation tests and drained triaxial compression tests with a constant stress ratio path is conducted on the coral sand to investigate the stress-strain curves and the behavior of particle breakage. The applicability of the power-law stress-strain model for the coral sand under the earth fill stress path is investigated, and the calculated results of the model are compared with the test curves. The results show that the stress-strain curves under both K0 consolidation and constant stress ratio paths conform to the form of power-law curves and can be described by a power-law nonlinear elastic model. The tangent modulus and tangent Poisson's ratio of this model can be expressed as a function of axial effective stress and can be determined by parameters related to the principal stress ratio or K0 coefficient. Under a constant stress ratio path, the tangent Poisson's ratio and tangent modulus increase with the increase of the axial effective stress. For the same axial effective stress condition, a large principal stress ratio corresponds to a large tangent modulus and a small tangent Poisson's ratio. With the increase of the axial effective stress under the condition of K0 consolidation, the coefficient of earth pressure at rest and tangent Poisson's ratio decrease, while the tangent modulus increases. Under the stress paths of K0 consolidation and constant stress ratio, the amount of particle breakage of coral sand within the test stress range is very small and therefore has little effect on the stress-strain curve. Under the constant stress ratio path, the stress-strain curve of coral sand in a certain stress ratio range can be reasonably predicted by the power function model, in which the effects of different constant stress ratio paths on the stress-strain relationship are considered.

In order to explore the slurry diffusion law of shield tail synchronous grouting in water-rich fine sand layer, start time of filter cake generation in the process of slurry diffusion is taken as the turning point of slurry permeation diffusion and compaction diffusion, and the theoretical formula of slurry permeation diffusion considering permeation effect and the theoretical formula of influence radius of slurry compaction diffusion are established. The similarity model test is carried out by the self-developed shield tail synchronous grouting system to verify the rationality of the theoretical formula. The results show that: (1) In the water-rich fine sand layer, different from the conventional single diffusion mode, the slurry is diffused in two stages of permeation-compaction. (2) The function of filter cake is to convert the slurry pressure in the form of pore pressure into effective stress acting on the soil skeleton, and after the filter cake begins to form, the slurry diffusion mode changes from permeation diffusion to compaction diffusion. (3) According to the change law of the effective stress conversion rate curve of the slurry pressure, the larger the grouting pressure, the shorter the time of filter cake formation, i.e. the shorter the duration of the slurry permeation diffusion. (4) With the increase in grouting pressure, the influence radius of slurry compaction diffusion stage also increases, e.g. the disturbance range of the stratum is about one times the tunnel excavation contour when the grouting pressure is 0.4 MPa through experiments and theoretical calculations,. The research results can provide theoretical support for synchronous grouting construction of shield tail in water-rich fine sand layer.

3D printing, a rapid prototyping technology, has great potential for applications in laboratory rock tests, but the low strength and stiffness of 3D printed samples have been one of the key problems that need to be addressed. In order to find a way to enhance the strength and stiffness of 3D printed rock-like samples, GS19 sand and furan resin were selected as printing materials, and sand 3D printed rock-like samples were used as research objects. Based on this, the samples were post-processed using three different methods: vacuum infiltration, low-temperature treatment, and combination of infiltration and low-temperature. Uniaxial compression tests were carried out on these post-processed sand 3D printed rock-like samples to study their mechanical properties, and the reasons for changes in mechanical properties were analyzed at a microscopic level by scanning electron microscopy. The results indicated that different post-processing methods can change the mechanical properties of the samples, and the combination of infiltration and low temperature can significantly enhance the strength and stiffness of samples, which is related to change in the internal cementation state of samples. The findings of the study can provide new research ideas for future application of 3D printing technology in rock testing.

Dispersive soil has the characteristic of being dispersed and lost when encountering water. In engineering practice, lime and cement are often used to modify dispersive soil, but doing so often has such problems as environmental pollution. The Si/Ca compound system composed of nano-silica sol and calcium chloride is selected as the modified material for dispersive soil. The effect of the modification is studied by pinhole test, mud ball test, and dispersion and disintegration test. The mechanism of dispersive soil modified by Si/Ca compound system is explored by physical and chemical properties tests. The results show that the dispersibility of soil can be completely eliminated by using nano-silica sol alone at 25% dosage or using calcium chloride alone at 0.40% dosage. However, the Si/Ca compound system composed of 1% nano-silica sol and 0.05% calcium chloride can also completely eliminate the dispersion of soil, which effectively reduces the dosage of the two materials used alone. The disintegration process of the soil modified by nano-silica sol modified is different from that of dispersive soil, with a shorter final disintegration time and a more stable disintegration rate. The final disintegration time is further shortened and the disintegration rate increases when the nano-silica sol and calcium chloride are used together. The mechanism of dispersive soil modified by Si/Ca compound system includes reducing the percentage of exchangeable sodium ions and the pH of the soil, and generating calcium silicate hydrate. The results demonstrate that the Si/Ca compound system composed of nano silica sol and calcium chloride can effectively modify the dispersive soil.

Tapered rigid core composite cement-soil pile is an emerging type of composite pile. In order to investigate its bearing behavior in engineering applications such as highways and railways under long-term cyclic loading, model tests were conducted on four composite piles with different pile core wedge angles, static loading ratios and cyclic loading ratios. The ultimate bearing capacity under static loading as well as the cumulative settlement, pile axial force distribution, tip resistance and side friction resistance were evaluated. The results indicated that the bearing capacity of tapered inner core composite piles under static loading was better than that of constant cross-section inner core composite piles. The cumulative settlement of composite piles increased with the increase of static loading ratio and cyclic loading ratio, and can be classified into three types of stability, development and failure under different combinations of dynamic and static loading. At the same time, the value range of load satisfying each type was also given. The interaction between the core pile and the cement-soil outer pile was not noticeably diminished, and the composite pile with a tapered core pile could fully mobilize the side friction resistance of the upper soil around the pile sides and effectively reduce the stress concentration at the tip of the core pile. Therefore, its ability to resist cyclic loading was better than that of the composite pile with a constant cross-section core pile.

Shallow deformation of ancient landslides induced by heavy rainfall is the most serious geological disaster in China's Three Gorges Reservoir Area (TGRA). It is important to explore the infiltration characteristics and its shallow deformation mechanism caused by heavy rainfall. In this study, the rainfall-induced landslide of the TGRA was selected as the research object, and the distributions of the soil permeability coefficients for rainfall-type landslide were summarized. Considering the effects of heavy rainfall, one-dimensional (1D) soil column infiltration test and two-dimensional (2D) landslide model test were conducted to study the infiltration characteristics of landslide soil and the corresponding shallow deformation mechanisms under different rainfall intensities. The results of the rainfall infiltration tests show that the speed of rainfall infiltration into soil depends on the magnitudes of rainfall intensity and soil permeability coefficient, i.e. when the rainfall intensity is less than or equal to the soil permeability coefficient, the infiltration capacity increases with rainfall intensity; when the rainfall intensity is greater than the soil permeability coefficient, the infiltration capacity decreases. The model test results show that the infiltration of heavy rainfall makes the surface soil transiently saturated and then the gas in the unsaturated zone below the surface is temporarily closed, which leads to the compression of gas by the surface pore water pressure. This means that the pore gas pressure increases with the infiltration of heavy rainfall. Overall, for the rainfall-induced landslides in TGRA, short-term torrential rain can create transient saturation zones and generate closing gas which is the main reason affecting the infiltration capacity of heavy rainfall. The water pressure transmitted by the closing gas causes the pore water pressure of the shallow soil to increase sharply, which is also the main reason for the shallow deformation and damage of many landslides.

There are few theoretical studies on lateral bearing capacity of flexible single pile under vertical-horizontal loading path in sand foundation and the influence of pre-applied vertical load on p-y curve is rarely considered. In view of this, the ultimate soil resistance of hyperbolic p-y curve was modified accounting for compacting effect of the sandy soil around the pile under the vertical force applied in advance. Cosine function was used to characterize the distribution of radial earth pressure on the passive side. The relationship between the maximum radial earth pressure on the passive side and the total soil resistance was proposed, and the analytical expression of the shaft resisting moment on the passive side was derived. Taking an included angle β  between the direction of friction resistance and the vertical direction into account, the variation of pile axial force induced by friction resistance was corrected and its computational formula was obtained. The differential equation of pile deflection was established considering the modified p-y curve, the variation of axial force caused by pile dead weight and friction resistance, the P-Δ effect and the shaft resisting moment. The numerical solution was obtained by MATLAB program. The correctness of the proposed method was verified by comparing the calculated results with the existing simulations and measurements. On this basis, the influence of vertical force applied in advance on lateral bearing capacity of single pile was discussed. The results show that the computational formula of the variation of pile axial force deduced in this paper can more accurately describe the influence of friction resistance on pile axial force and can be used for large deformation conditions. The vertical force applied in advance can enhance the lateral bearing capacity of flexible single pile. The enhancement gradually decreases with the increase of the vertical force applied in advance.

The importance of long-term stability of any structure makes the time effect of soil is one of the most concerned problems in geotechnical engineering. In this study, the creep tests on the equivalent sand particles of three-dimensional (3D) printed rods under lateral confined condition are conducted. In the tests, the internal particle motion characteristics of dense sand during creep and its relationship with macroscale creep deformation are explored from the perspective of single particle motion and contact motion between particles based on the close-range photogrammetry and particle image velocimetry (PIV) technology. The test results show that the 3D printed rod can reflect the macroscale deformation characteristics of dense sand during creep well. Under the lateral confinement, the creep deformation increases with the increase in time and decreases with the increase in creep stress, and the creep rate decreases and tend to be stable at the initial and secondary creep stages. This can be explained by that at the initial stage of creep, the particles move downward and rotate greatly which makes the pores between particles obviously reduced, and the creep deformation is mainly induced by the compression of pores between particles; then, the pores between particles do not decrease obviously and tend to be stable, the particles move in irregular directions, which indicates that the creep deformation is mainly controlled by local particle position adjustment and rearrangement. This also reveals that the macroscale creep deformation is closely related to the microscale translational change of particles. The contact motion between particles increases obviously with increasing time. During creep, contact rolling and contact sliding occur simultaneously, and gradually concentrate on some contacts that are easy to move. There is a good linear relationship between the average contact sliding distance and rolling distance of the strong moving contacts, i.e. with the increase of time, the average contact sliding distance is gradually greater than the average contact rolling distance, indicating that the sliding produces volume contraction and controls the macroscale creep deformation.

In recent years, the slurry shield method has been extensively used for tunneling under seas or rivers. In the process of slurry shield construction, opening the chamber under air pressure has always been a high-risk and difficult task. The key to the success of opening the chamber under air pressure lies in the filter cake airtightness property. However, there has been less theoretical research on the mechanism of failure of filter cake airtightness property, airproof time and its influencing factors. Therefore, considering the effects of air pressure and pore water, we establish a transient mechanical model "percolation initiation–failure under air pressure" of filter cake based on multiphase flow theory, and propose a method for predicting water discharge mass through filter cake and airproof time under air pressure. Then, we conduct the laboratory filter cake airproof test to verify the applicability of the proposed theoretical approach. Finally, the influences of air pressure, stratigraphic parameters, filter cake thickness, slurry shear strength and other parameters on filter cake airproof time are discussed, and the results reveal that the airproof effect mainly depends on the filter cake under air pressure, followed by infiltration zone. This study can provide some reference for the safety of opening chamber under air pressure in slurry shield.

In order to understand the load transfer mechanism of highway bridge pile foundation passing through karst cave, the field test of bridge pile foundation treated by backfilling method is carried out. Combined with the numerical simulation method, the vertical bearing characteristics and load transfer mechanism of pile foundation passing through karst caves with different heights are studied, and the variation law of the maximum value of the negative skin friction caused by backfilling material in different cave heights and its proportion of distribution range are discussed. The results show that the negative skin friction in the karst area is affected by the type of karst cave, i.e. when the settlement of the soil on the side of the pile of the filled karst cave is smaller, the pile side can provide less positive friction for the pile foundation; when the settlement of the soil of the pile side of the unfilled karst cave is larger, the pile side can produce negative friction. After the karst cave is treated by the backfilling method, the vertical ultimate bearing capacity of the bridge pile foundation passing through the karst cave decreases with the increase of the cave height, e.g. when the cave height increases from 3 m to 12 m, the distribution range of the negative skin friction corresponding to the vertical ultimate bearing capacity of pile foundation increases from 0% to 27.14%. It is suggested that in the actual design, when the backfilling method is used to deal with the karst cave, the influence of the negative skin friction caused by the pile foundation passing through the karst cave on the vertical bearing characteristics of the pile foundation should be considered. When the height of karst cave is 3–12 m, the bearing capacity of the pile foundation should be calculated according to negative skin friction in the ranges of 0, 0.106H, 0.214H and 0.271H (H is the cave height) below the top surface of karst cave, so as to ensure the bearing safety of bridge pile foundation during the consolidation and settlement of backfill materials after cave treatment.

Loess is a type of soil with metastable structure. Due to the inhomogeneity, anisotropy, disturbance of in situ sampling and repeated variability of tests of undisturbed loess, how to manually prepare a structured loess that can more accurately reflect the mechanical properties of undisturbed loess is worth studying. Based on the existing methods of preparing structured soil by adding cement, lime and new rock and soil materials Roadyes to remolded loess, this study investigates the influence of different binders on the mechanical properties of artificial structured loess. The research results show that the structural strength of the structured soil prepared with Roadyes as the binders increases first and then decreases with the increase in Roadyes content, which is different from the characteristics that the shear strength of cement and lime increases continuously with the increase in the addition amount. Under different confining pressures, the evolution of the stress–strain curve of the structured soil prepared with Roadyes is more consistent with the mechanical properties of the undisturbed loess. The variation of shear strength of structured soil prepared with three binders can be divided into steep drop stage and stable stage with the change of water content. At the steep drop stage where the water content is less than the plastic limit, the shear strength decreases sharply, but changes slowly at the stable stage, which resembles the remolded soil. Different binders have little influence on the friction angle φ  of artificial structured loess, but have significant influence on the cohesion c. The research results are helpful to understand the soil mechanical properties changed by common binders, and also provide theoretical and technical guidance for the preparation of artificial structured loess with preset mechanical parameters.

Calculation of unloading-induced upheaval deformation of the foundation pit is of great significance to the stability analysis of the foundation pit. The exponential function between rebound modulus of soil and unloading ratio is deduced based on the existing laboratory test results of the soil compression–rebound test and published results of silty clay foundation pits in different areas. Then, a simplified calculation method for upheaval deformation is proposed by combining the Mindlin’s solution and the layer-by-layer summation method. The accuracy of the proposed method is validated using the results of two engineering examples. It is found that by using the simplified calculation method, the upheaval deformation induced by foundation pit unloading can be easily predicted only using soil parameters obtained by conventional geotechnical tests, and the predicted results of this method are close to the measured values. The further analysis shows that when the shape of the foundation pit is the same, the upheaval deformation at the bottom of the foundation pit nonlinearly increases with the linearly increase in the area of the foundation pit; when the area of the foundation pit is the same, the upheaval deformation of the strip foundation pit is smaller than that of the square foundation pit. The proposed method can provide theoretical guidance to the upheaval deformation prediction of the foundation pit in the silty clay area.

Reinforced earth retaining walls, as part of the roadbed, are not only subjected to static loads such as road infrastructure, but also subjected to traffic loads caused by vehicle movements. To investigate the mechanical properties and working performance of modular reinforced earth retaining walls under static and dynamic loads, the large-scale laboratory model tests were conducted, in which the variation laws of the mechanical behaviors such as the settlement of reinforced earth retaining walls, horizontal displacement of panels, lateral earth pressure coefficient and geogrid strain were compared and analyzed. The results showed that the damage modes of retaining walls under static and dynamic loads are local shear damage and panel extrusion damage, respectively, and the maximum strains of the geogrid are 1.7% and 4.5%, respectively, neither of which reaches the damage strain. The ultimate bearing capacities of the retaining wall under both static and dynamic loads are identical, and the maximum settlement of the top of the wall under dynamic load is increased by 280% and the horizontal displacement of the panel is increased by 180% compared with those under the static load. The deformation of the surrounding soil by extrusion during the descent of the load plate imposes horizontal additional stress on the panel, resulting in a larger lateral additional stress coefficient K_r than the theoretical value at the back of the wall. Under the action of dynamic load, the soil particles move irregularly, and the peak acceleration in the soil increases with the increase in load amplitude and decreases gradually from top to bottom along the height of retaining wall. The research results are important in revealing the mechanical behavior and damage mechanisms of reinforced earth retaining walls under static and traffic loads and in improving the relevance of model tests to actual engineering.

A three-dimensional viscous fluid-pile-soil interaction analysis model is established to analyze the vibration response of pile foundation in liquefied soil under simple harmonic excitation horizontal dynamic load. The liquefied soil around the pile is regarded as viscous incompressible fluid, and the fluid motion equation is established. The analytical expressions of viscous fluid dynamic pressure and fluid velocity potential are obtained by using Helmholtz decomposition and variable separation method, combining fluid boundary conditions, pile-fluid displacement, velocity continuity conditions and pile boundary conditions, so as to obtain the expression of pile resistance. The saturated unliquefied soil layer is simulated using the saturated porous medium model. Based on the existing analytical solution of vibration response of saturated unliquefied soil layer, the analytical solution of pile top impedance of horizontal vibrating pile foundation in saturated unliquefied soil is derived. The correctness of the solution of the proposed model is verified by comparing with the free vibration solution of the existing cantilever beam in water. Finally, the effects of fluid viscosity coefficient, pile length and pile-soil modulus ratio on pile top impedance are analyzed. The results show that neglecting the viscosity characteristics of liquefied soil will overestimate the stiffness and impedance of pile foundation and underestimate the damping impedance.

In order to understand the strain hardening and damage self-healing properties of salt rock, the mechanics test, porosity and permeability tests and nuclear magnetic test were performed. The mechanical properties, permeability, porosity and pore size distribution under strain hardening and damage self-healing conditions were investigated after being maintained at room temperature and confining pressure. The results show that: (1) Strain hardening of damaged salt rock weakens the plasticity of rock samples, decreases the peak strain under secondary loading, and increases the elastic modulus. With the maintenance at room temperature or confining pressure, the salt rock self-healing occurs, and the plasticity gradually recovers, while the peak strain increases and the elastic modulus decreases under secondary loading. (2) The stress–strain curves of intact and damaged salt rocks almost have no compacting stage, while the stress–strain curves of intact and damaged salt rocks show obvious compacting stage after long-term maintenance at room temperature and confining pressure. (3) The permeability and porosity of the intact salt rock are very low, and the permeability of the damaged salt rock is two orders of magnitude higher than that of the intact salt rock. With the increase of the maintenance time at room temperature, the permeability and the porosity decrease slowly. The permeability of damaged rock after being maintained at confining pressure is restored to the same order of magnitude as that of intact rock. (4) After being maintained at room temperature and confining pressure, part of the middle pores and large pores healed into small pores and middle pores. (5) Slow self-healing of damaged salt rock occurs when the salt rock is maintained at room temperature, and the confining pressure can greatly improve the speed of self-healing of damaged salt rock. (6) The damage self-healing of salt rock can be divided into rapid recovery stage and slow recovery stage in the later stage.

The dynamic response of harmonic load acting on the soil-lining system in cold regions considering anisotropic frost heave is studied in frequency domain. The lining is in close contact with the frozen soil and there exists relative movement between the frozen soil and unfrozen soil due to differences in composition and properties. An analytical solution of the vibration induced by the harmonic load in frozen soil is obtained considering the anisotropic frost heave in soil. Based on the continuity and boundary conditions between the unfrozen soil, frozen soil, and lining, the coefficients to be determined are obtained and the analytical solutions for the displacements and stresses in the different media of the tunnel system in cold regions are also obtained. The analysis of specific parameters of the model shows that the change in the parameters of the tunnel system (lining, frozen soil, and unfrozen soil) affects the amplitude of the circumferential stress, the amplitude of the radial displacement in the soil in different states and their peak frequencies in cold regions; anisotropic frost heave affects the stresses in the frozen soil; the amplitude of the radial displacements in the tunnel system in the cold regions decays with increasing distance from the center of the tunnel, and the amplitude of radial displacement in unfrozen soil decreases considerably compared to that of frozen soil.

To examine the mechanical properties of frozen soil under the influence of complex stress paths, a triaxial apparatus is applied to conduct compression tests under different loadings. The corresponding stress states involve generalized triaxial compression stress state, plane strain state and true triaxial stress state. The strength evolution law and deformation of frozen sand in the presence of various stress states are methodically explored. The obtained results reveal that for a constant minor principal stress, the strength of frozen sand and the slope of the stress-strain curve increase in the order of generalized triaxial compressive stress state, plane strain state and true triaxial stress state, respectively. Furthermore, the minor principal stress is capable of enhancing the strength of the frozen soil. The expansion deformation always occurs in the direction of minor principal stress. As the major principal strain grows, the volumetric strain initially shrinks and then expands. For the same test, minor principal stress has a trivial influence on the volumetric strain. Under the same test loading conditions, the smaller the minor principal stress is, the higher the ratio of deviatoric stress to spherical stress is. The failure strength of the sample enhances from the generalize triaxial compression stress state to the plane strain stress state, and then to the true triaxial stress state.

During underground mining of metal resources, the surrounding rock of the goaf is deformed and damaged, which will affect the safety of underground mining. The failure mechanism of surrounding rock in the underground goaf at Jinshandian East District is studied by means of field investigation, displacement monitoring, microseismic monitoring and theoretical analysis. Considering the influences of horizontal in situ stress and caving rock mass, the failure mechanisms of surrounding rock of the goafs in the hanging wall and footwall are obtained, i.e. toppling–slipping failure and buckling–slipping failure, based on limit equilibrium theory and energy method, respectively. Under the cutting action of the steeply dipping discontinuities, the surrounding rocks of the hanging wall and footwall form an anti-dip structure and a forward-dip structure, respectively. Under the action of horizontal in situ stress, the rock mass with steeply dipping discontinuities in the hanging wall topples to the side of the goaf, and the deformation and damage of the rock mass leads to the activation of the fault F4. As the mining deepens, the number and extent of the failure rock mass continues to increase, and a deep slip surface is formed and traversed the fault F4. Under the action of horizontal in situ stress, the surrounding rock of the goaf in the footwall induces the slip of the fault F1 at the boundary of the ore body, and simultaneously causes the buckling–slipping failure of the rock column with forward-dip discontinuities, and forms a slip plane along the discontinuity surface.

With the rapid development of nuclear power plant constructions, it has become an unavoidable issue to choose a soil site as the plant site. Soil-pile-structure interaction (SPSI) effect has an important influence on the seismic safety evaluation of a nuclear island structure (NIS). A 3D integrated simulation method is developed to evaluate the seismic responses of a pile-mat-founded AP1000 nuclear-island building system subjected to multidirectional earthquake motions. Considering the regional tectonic setting and historical seismicity around the plant site, a set of three-component recordings for scenarios near-field moderate-strong, moderate-far field strong, and far-field large earthquakes are selected and justified for determining the bedrock shakings used in this study. The whole nonlinearity including both the primary and secondary nonlinearities of soil and only the primary nonlinearity of soil are considered by one-step method and two-step method for performing the 3D response analysis of the SPSI system, respectively. The quantitative influence of soil secondary nonlinearity (SSN) on the NIS seismic responses (i.e., SSN effect) under earthquake scenarios can be obtained by comparing the results obtained from the above two methods. A finding is that the influences of SSN on the horizontal seismic responses of NIS are obviously greater than those of the vertical ones of NIS, and the SSN effect makes the SPSI system more flexible. The SSN effect is strongly related to the characteristics of bedrock shaking scenarios and is the largest under the near-field moderate-strong earthquake scenarios. Given SSN effect can significantly increase the NIS seismic responses, the SSN effect should not be ignored in the NIS seismic design.

Floor heave is a common disaster in deep soft rock tunnel engineering with high in situ stress. The stress release, transfer and concentration in surrounding rock caused by tunnel excavation are often ignored in the current floor heave mechanism, and only the initial in situ stress state is analyzed. Therefore, in view of the superiority of the combined finite-discrete element method (FDEM) in simulating the elastoplastic continuous deformation, the discontinuous deformation (fracture failure) and the contact action between the rock fragments, FDEM is employed to study evolutionary mechanism of the progressive fracture and swelling deformation of tunnel floor. In addition, the influences of the lateral pressure coefficient, the tensile strength of the surrounding rock mass and the position of the floor on the heave mechanism are also investigated. The simulation results indicate that: (1) The floor heave mechanism is the progressive fracture and swelling deformation of tunnel floor, which can be briefly described as that tunnel excavation leads to a release for the radial stress and a concentration for the tangential stress. When the increased tangential stress exceeds the strength of the rock mass, conjugate shear cracks appear and are accompanied by tensile cracks. The maximum tangential stress continues to evolve into the depth of the intact surrounding rock until it reaches an ultimate equilibrium state with the strength of the rock mass, and the shear cracks also continue to propagate into the deep. The deep fragments push the shallow fragments to move into the tunnel space and create a large number of gaps, resulting in volume expansion and floor heave disaster eventually. (2) According to different lateral pressure coefficients and tensile strengths, five types of floor failure modes can be summarized, but all of them can be considered as the fracture and swelling deformation caused by the maximum tangential concentrated stress. The limitations in the previous floor heave mechanism which did not consider stress evolution phenomenon including stress release, transfer and concentration are improved. A new floor heave mechanism based on progressive fracture and swelling deformation is proposed, which provides a new perspective for the study on the floor heave mechanism.

The thermal-moisture dynamics of permafrost and cold region engineering caused by the trend of warming and humidification of the Qinghai-Tibet Plateau (QTP) are the focus of research on permafrost ecological and geological evolution in the third pole. Currently, the model of permafrost ground surface energy budget under the influence of rainfall does not consider the influence of rainwater temperature and neglects the effect of rainfall energy pulse. On the basis of the previous frozen soil hydro-thermal coupling theory, a permafrost hydrothermal coupling model considering the rainfall energy was constructed by introducing the surface energy equilibrium theory considering the rainwater sensible heat. Based on the on-site monitoring data of the Beiluhe in the QTP, the validity of the model was verified, and the influence mechanism of the summertime rainfall on the ground surface energy equilibrium and the thermal-moisture dynamics of the active layer was analyzed. The results show that the average deviation errors of soil volumetric water content, temperature, and heat flux simulated by the modified model considering rainwater sensible heat are within ±1.198%，±0.704℃, and ±1.66 W/m2, respectively, and the consistency indexes are greater than 0.877, 0.929, and 0.937, respectively. The optimized model improves the assessment of the surface heat absorption or heat release state and can better predict the thermal-moisture dynamics of the active layer after rainfall. Summertime rainfall increases the surface evaporation latent heat and rainwater sensible heat but reduces the surface net radiation, sensible heat, and soil surface heat flux to cool the surface. The cooling efficiency is positively correlated with rainfall intensity. In addition, it is affected by the time of occurrence of the rainfall. The daytime rainfall has a significant cooling effect, and the rainwater sensible heat promotes the cooling of the surface. The rainwater at night temporarily heats the surface, but the significant effect of evaporation latent heat makes the ground surface continuously cool. Due to the reduced surface temperature gradients and the infiltration of rainwater, the decrease in the thermal vapor flux densities, the increase in the liquid water flux densities promote the downward transportation and accumulation of liquid water during heavy rainfall events and continuous rainfall events. However, compared with the increased convective heat exchange of liquid water, the reductions of heat conduction, latent heat of water vapor diffusion, and water vapor convective heat are more significant, which reduces the total soil heat flux, decreases soil temperature, and mitigates the warming rate for the active layer.

Wave-induced seabed response is a research hotspot in the field of geotechnical engineering. The wave-induced seabed liquefaction is the main reason for the instability of seabed and marine structures. In view of many uncertainties involved in the analysis of the seabed response, such as the spatial variability of sediment properties and the randomness of related loads, a probabilistic framework based on the stochastic finite element method is developed, which couples the simulation of spatially heterogeneous soil in MATLAB and the finite element analysis of poroelasticity in COMSOL through the LiveLink program. A decomposed K-L expansion method is proposed, which takes less computational time and memory space, making the generation of three-dimensional random fields with high resolution and large scale more effective. Based on the proposed probabilistic framework, the dynamic response of both the two-dimensional sloping seabed under regular waves and the three-dimensional seabed under random waves are studied. The influence of the spatial variability of the permeability coefficient K and shear modulus G of marine sediments and the randomness of wave loads on the distribution of pore water pressure and the liquefaction depth in the seabed are revealed. The study has shown that traditional deterministic analysis methods lead to unsafe engineering designs.