With regard to undrained analysis of saturated clay foundation for its ultimate bearing capacity under rapid loading, this study has proposed the calculation of the unconsolidated-undrained (UU) strength instead of employing the consolidated-undrained (CU) strength parameters directly due to overestimated results. The formula for predicting UU strength has been deducted based on the CU strength parameters referring to the reports of geological investigation, and the profile of the UU strength , found increases linearly with depth, has been built up. A calculation method for the bearing capacity of this foundation type is therefore proposed. The basic idea thereof is to use the value of at the average depth of the slip plane in the calculation, and a dimensionless parameter, which plays the key role, is introduced to determine the maximum depth of the slip surface. The accuracy and the precision of this parameter, as well as the proposed method, has been validated via a large number of comparative calculations with the finite element limit analysis method in this study.

The buffer blocks used in deep geological repositories of high-level radioactive wastes (HLW) should be cured in an appropriate environment to prevent the deterioration of buffer blocks such as desiccation shrinkage and cracking. In this study, the bentonite-sand mixtures with different initial moisture contents (11.23%-21.63%) were compressed in the laboratory to simulate the production of buffer blocks. The bentonite-sand mixtures were cured at different relative humidity (RH) of 33%, 75%, 85% and 100% in order to find the optimum curing humidity. During the curing process, the periodical mass change was weighed by a balance, the size change was measured by a vernier caliper, and the thermal conductivity was tested after the curing was balanced. The test results indicate that the moisture variation of bentonite-sand mixtures during curing was consistent with the soil-water characteristic curves (SWCCs) of the mixtures. When the compacted bentonite-sand mixtures were cured at the relative humidity of 33%, 75% and 85%, the samples were dehydrated and became dried, resulting in desiccation shrinkage and cracking. When the relative humidity was100%, the mixtures with a lower initial moisture content of 11.23%-14.99% tended to absorb moisture from the environment and swelled. While the mixtures with a higher moisture content of 17.22%-21.63% were desiccated to shrink, but no obvious cracks were observed on the surface of these cured specimens. Under the curing condition of RH = 100%, the variation of water content and volume of the sample with an initial water content of 17.22% was the minimum, which was considered as the optimum curing humidity for buffer blocks. The optimal curing conditions (optimum RH) of industrial-scale buffer blocks used in the disposal repository can be estimated by the SWCCs of the small buffer blocks, and the development of drying shrinkage crack can be quantitatively evaluated by the thermal conductivity of buffer blocks.

The damage evolution and deformation characteristics of marble are studied by cyclic loading and unloading tests with varying amplitude under different confining pressures, and the crack volumetric strain and dilatancy characteristics are analyzed emphatically. Some conclusions are drawn as follows. (1) With the increase of cycle number, the elastic modulus of marble first increases and then decreases, and the generalized Poisson's ratio first stabilizes and then increases rapidly. (2) Comprehensive analysis of the crack volumetric strain curves from the 3rd to 6th loading shows that as the number of loading increases, the initial crack volumetric strain of the marble increases, the initial position of elastic deformation stage is delayed, and the expansion point gradually advances. Moreover, the relationship between the increment of crack volumetric strain caused by a single cycle and stress amplitude is exponential. (3) The dilatancy index of variable amplitude cyclic loading and unloading is different from that of monotone loading at a high confining pressure. With the increase of confining pressure, the proportion of crack volumetric strain increases gradually, and the proportion of crack volumetric strain under variable amplitude cyclic loading and unloading is greater than that under monotonic loading. The failure mode of marble changes from shear failure under monotonic loading to bulging failure under variable amplitude cyclic loading and unloading.

The characteristics of the slip surface of the soil are highly important for the calculation of earth pressure. In order to study the characteristics of the limited width soil active slip surface behind the rigid wall, laboratory model tests were carried out using non-cohesive sand, the images of soil during the test were collected and analyzed by digital image correlation method, the shear strain and displacement of soil are obtained, and the translation (T-mode) and rotation around the bottom of the wall are analyzed. The research results show that the critical aspect ratio of active soil with limited width is similar in T mode and RB mode, while in RT mode, the critical aspect ratio is relatively small; the active sliding surface of the soil with limited width in T mode presents the characteristic of "multi-refraction lines". According to the similarity of the sliding angle, it can be divided into the slip surface developed from the mobile retaining wall and the fixed retaining wall, the starting point of the active slip surface of limited-width soil in RB mode is the upper part of the wall heel, and the starting point of the RT mode is the wall heel, both of which extend to the middle of the fixed retaining wall. Obvious soil arch characteristics can be observed in the horizontal and vertical displacement of soil with limited width in T mode and RT mode, and the edge of soil arch is the sliding surface.

Fully grouted rock bolts are widely used in mining and civil engineering. In this study, numerical simulation was adopted to study the loading transfer performance of fully grouted rock bolts. First, based on the shear failure behaviour of the interface between the bolt and grout, a bond-slip model considering the residual shear strength was developed. Then, it was incorporated into the structural elements of piles. After that, the experimental pulling tests of rock bolts were carried out to validate the accuracy of this bond-slip model and the corresponding numerical modelling results. Finally, the influence of the residual shear strength, the shear stiffness coefficient and the grouted length on the bolting performance was studied through the validated numerical model. The results showed that the interfacial residual shear strength had a significant effect on the maximum and residual bearing capacity of rock bolts, which cannot be neglected in the test. With the increasing of interfacial shear stiffness coefficient, the maximum bearing capacity of bolts remarkably increased, and meanwhile there is no observable effect on the residual bearing capacity of bolts.

Deformation and strain are the objective mechanical responses of materials when the stress or external environment changes, and the description of this property is subjective. The conventional representation of strain state consists of three normal strains and three shear strains, which is inconvenient in testing and expression. In order to find a new method to express the strain state——a more universal shear strain generalized angular strain is proposed based on the shear strain. In this paper, the generalized angular strain is defined as the change of radian at any angle and is no longer limited to the right angle. On this basis, the relationship between the generalized angular strain and the expression of the conventional strain state is established based on the expression of the change of any angle in the strain theory, and the conditions and specific methods for the calculation of the conventional strain state from the generalized angular strain are given. By considering the uniform distribution of directions, the generalized angular strain representation based on tetrahedron and equal right angle tetrahedron are studied. According to the given method, the conventional strain state can be expressed as these two generalized angular strains, and the corresponding conventional strain state can also be obtained from these two generalized angular strains. Thus, a single representation of strain state is realized, that is, only six generalized angular strains can be used to represent three-dimensional strain state without the joint form of three positive strains and three shear strains. The research results of this paper provide a new idea for the development of strain state testing methods and the research of constitutive model.

The elastic solution and the unified plastic solution for the frost heaving force of tunnels in cold region as well as the implicit equation of plastic zone radius were proposed in this study based on the overall freeze-thaw circle frost heave model. The proposed solution can comprehensively account for the influences of the intermediate principal stress, the transverse isotropic frost heave and the displacement release of surrounding rock. Meanwhile, an approach was provided to determine the elastic-plastic state of frozen surrounding rock. Furthermore, comparability analysis and verification of the proposed solution were performed. The effects of various factors on the frost heaving force and plastic zone radius were investigated. Finally, the distance description of the surrounding rock displacement release was quantified through the supporting time. It was found that the proposed solution has good comparability and was verified by model tests in reference. As the yield criterion of frozen surrounding rock, the unified strength theory can fully make use of its bearing potentiality, the frost heaving force and plastic zone radius are decreased obviously. The frost heaving force and plastic zone radius are significantly affected by the anisotropic frost heave coefficient and the volume frost heave ratio. Therefore, it is necessary to consider the transverse isotropic frost heave of surrounding rock and take effective measures of tunnel waterproofing and drainage as well as insulation and frost resistance. The frost heaving force is large when the displacement release coefficient is small, while the plastic zone radius reaches its peak value when the displacement release coefficient reaches one. Therefore, a proper supporting time is beneficial to the safety of construction and operation for tunnels in cold region. The obtained results can provide some theoretical guidance for the design of tunnels in cold region.

A series of consolidated drained triaxial shear tests was carried out on compacted loess samples under different drying and wetting cycles to study the structural constitutive relationship considering the effect of drying and wetting cycles. The results indicated that the triaxial shear mechanical properties of compacted loess in different structural states were significantly different, which is indicative of obvious structural characteristics. Based on the analysis of the triaxial shear stress-strain relationship curves of compacted loess under different drying and wetting cycles, the triaxial shear structural parameters of drying and wetting cycles were defined according to the theory of comprehensive structural potential, and the rationality of the parameters was verified. The structural parameters were transformed and introduced into Duncan-Chang model to establish structural Duncan-Chang model which includes the effect of drying and wetting cycles. The comparison results showed that the calculated value of the constitutive model was basically consistent with the experimental value, which verified the rationality and applicability of the structural constitutive model. In accordance of the constitutive relation and parameters in this paper, taking a loess filling project as an example, the preliminary numerical analysis of which showed that the drying and wetting cycles had a great influence on the deformation of the filling foundation.

To investigate the effects of distributed diametral pressures on fracture parameters of a centrally cracked Brazilian disc (CCBD) specimen, the complex potentials theory and weight function method were adopted to derive the mixed-mode I/II fracture parameters of CCBD specimens subjected to five types of distributed loads. Based on the analytical solutions for fracture parameters, the effects of pressure distribution form and pressure distribution angle on stress intensity factors under mode I / II and T stress were investigated. The results show that the pressure distribution form has a remarkable influence on the geometric parameters, YI, YII and T* , with the relatively larger pressure distribution angle and crack length. The YI and T* under pure mode I and the YII under pure mode II both decrease as the pressure distribution angle increases, while the T* under pure mode II increases with an increased pressure distribution angle. When the pressure distribution form is a constant function, the pressure distribution angle has the most obvious effect on geometric parameters, while the degree of the influence reduces greatly for quartic polynomial function. The critical fracture angle under pure mode II is less affected by the pressure distribution form and pressure distribution angle, while the crack length has a significant effect on it.

Water-rock interaction has a significant influence on the strength characteristics of soft rock. In this paper, the uniaxial compression test and point load test were conducted on typical Cenozoic red sandstone that was taken from Chizhou City, Anhui Province, China. The empirical conversion coefficient between point load strength (PLS) and uniaxial compression strength (UCS) and the softening law of water content on PLS were studied. Meanwhile, the softening mechanism of this sandstone was also discussed based on the analyses of mineral composition and microscopic structure as well as the results of water absorption tests. The resultes show that: (1) in the natural state, the empirical coefficient for converting the point load strength to uniaxial compressive strength of the Cenozoic red sandstone should be appropriately reduced, and it is recommended to take 9.0; (2) The PLS and penetration ratio decreased with the increase of water content, showing a trend of negative logarithmic decay; (3) The characteristic value of saturation of water absorption softening is put forward. This value divides the water absorption softening area into sensitive and non-sensitive areas, and the strength in the sensitive area changes dramatically with the change of water content. (4) The swelling-softening effect of clay minerals is the micromechanism appearing strength softening. Therefore, the characteristic saturation value should be universally suitable for soft rocks containing lots of clay minerals. (5) The Cenozoic red sandstone has a high clay mineral content and more internal microfractures. Because of clay minerals' water-absorbing expansion, crack expanding, and developing, the overall cementation ability of the rock is weakened and the structural system is destroyed, resulting in the reduction of the overall rock strength. This study provides a reference and basis for analyzing strength softening mechanism and strength softening parameters selection in the red sandstone field.

The placement of an incompressible cushion on the top of soft soil deposits affects the boundary drainage conditions. It has been well documented in the literature that the seepage through soft clays deviates from Darcy's law, which affects the dissipation of excess pore water pressure. However, the studies on the soil consolidation behavior under the partially permeable boundary condition induced by the incompressible cushion underlain by soil deposits considering the non-Darcian flow with the threshold hydraulic gradient have rarely been reported. In this study, a one-dimensional consolidation model under the partially permeable boundary condition and the time-dependent loading is developed. The effect of the threshold hydraulic gradient on the water flow through the soft soil is taken into account. The analytical solution is derived for the proposed consolidation model based on the eigen value method and Laplace transform. Based on the derived analytical solution, the sensitivity analysis has been conducted for the consolidation behavior under various boundary conditions, threshold hydraulic gradients and loading rates. It indicates that the smaller the partially permeable boundary parameter ? (i.e., the ratio of the product of the coefficient of permeability of the incompressible cushion and the thickness of the clay deposit to the product of the coefficient of permeability of the clay deposit and the thickness of the incompressible cushion, which indicates the permeability of the partially permeable boundary)is, the slower the dissipation of excess pore water pressure and the longer the duration of consolidation process are; the larger ? is, the faster the dissipation of excess pore pressure and the shorter the duration of consolidation process are. The larger the dimensionless variable R (the ratio of the product of the threshold hydraulic gradient, the unit weight of water and the thickness of soil layer to the surcharge) is, the longer the time when the seepage front (i.e., moving boundary) reaches the bottom of soil layer is, and the greater the residual excess pore water pressure at the end of consolidation is. At a given time, the settlement-based average degree of consolidation increases with an increase in the dimensionless variable R. On the contrary, the excess pore water pressure-based average consolidation degree decreases as the dimensionless variable R increases. The loading rate significantly influences the consolidation behavior of soils with threshold hydraulic gradient under the partially permeable boundary condition. It is found that the slower the loading is, the lower the peak value of excess pore water pressure is, and the longer the time it takes to reach its peak is. However, the loading rate has negligible influence on the residual excess pore water pressure.

In order to study the mechanical properties and failure mechanisms of the rocks with groups of holes and flaws, we use the 3D sand printing technique to prepare the rock-like specimens that each contains one hole and two flaws. We use the digital image correlation (DIC) method to monitor the full field of the specimens during their compression process without any contact. By calculating the matrix of the horizontal, vertical and shear strain, we introduce the effective variance of the strain field, which can be used to quantify and identify the failure behavior of the specimens. The main results are listed as below. The mechanical properties of the standard 3D sand printed specimens are similar to those of natural sandstones, and the variations of their mechanical properties are considerably low during the experiments. Therefore, they can be grouped as a rock-like material. Due to the inclusion of the flaws, the mechanical properties of the specimens are degraded. The compressive strength and elastic modulus are reduced by 8.04%-38.91% and 14.44%-27.78%, respectively, compared with those of the specimens containing no flaw but only one hole. Based on the results of DIC, three basic types of cracks are identified successfully, that is, tensile crack (Mode I), shear crack (Mode II) and tensile and shear mixed crack (Mode I-II). The failure patterns of all the specimens with one hole and two flaws show tensile and shear mixed crack (Model I-II). The coalescence patterns between the hole and the flaws can be influenced by their horizontal distance. Those patterns can be classified into tensile coalescence, rotation coalescence and shear coalescence. The discreteness of the strain field can be quantified by the effective variance of strain field comprehensively. The effective variance of the strain field is close to zero at the initial crack closure stage and the elastic deformation stage. It grows differently after the appearance of cracks. Based on the effective variance of the strain field, we propose a quantitative method to identify the type of crack. The cracks can be identified as tensile crack, tensile and shear mixed crack, and shear crack, respectively, when the growth rate of the effective variance falls into the ranges between 0.72×10–2 and 1.89×10–2, between 2.34×10–2 and 3.59×10–2, and between 9.63×10–2 and 32.40×10–2, correspondingly.

In the process of treating the dredged slurry under vacuum preloading combined with the prefabricated vertical drains (PVDs), a dense “soil column” with low permeability will be formed around the PVD, which results in a poor drainage condition and an unsatisfactory treatment (i.e., the clogging effect). In this study, in order to predict the consolidation behavior of dredged slurry with different initial water contents, the compressibility and permeability of dredged slurry with different initial water contents are investigated. Based on the compression and permeability curves obtained by laboratory tests, the analytical solution to soil consolidation under vacuum preloading is derived. Both the clogging effect and the effect of the initial water content on the initial effective stress are considered. The developed analytical solution is validated through a series of consolidation tests of dredged slurry under vacuum preloading with different initial water contents. It shows that at a given vacuum preloading, the dissipation rate of excess pore water pressure in the dredged slurry decreases as the initial water content increases. The proposed analytical solution presents reliable predictions on the variation of settlement and degree of consolidation with time in the dredged slurry with different initial water contents under vacuum preloading.

Rockburst caused by underground engineering excavation has obvious time-lag effect. Previous research shows that the occurrence of hysteresis rockburst is closely related to the time-lag damage of the rock. Based on this, considering that the surrounding rock is at different stress levels after excavation, the time-delay uniaxial compression test is carried out to analyze the time-delay deformation and failure characteristics of rocks under different stress levels. The results show that the stress level has a significant impact on the time-delay deformation and failure of rocks. As the stress level increases, the failure incubation time decreases exponentially, but it is much longer than that of conventional uniaxial compression failure. In the case of delayed uniaxial compression failure, the hoop strain and volume strain of the rock sample are significantly greater than that of conventional uniaxial compression test, and when the stress level is lower than 90%, the hoop strain at failure rapidly increases and exceeds the axial strain, which is also the distinguishing feature of time-lag failure and conventional uniaxial compression failure. The total energy of delayed uniaxial compression failure is equivalent to that of conventional uniaxial compression, but the proportion of dissipated energy increases significantly in the process of delayed loading, indicating that the delayed loading stage will lead to the significant development of damage in the rock. The rapid growth of circumferential strain of rock samples in the stage of time-delay loading leads to the significant increase of near axial splitting tensile failure cracks, which also leads to the more serious fragmentation of rock samples. The relevant research results can provide a good reference for the analysis and interpretation of time-dependent and time-lag rockburst of rock damage and failure under high stress level.

The load transfer efficiency of geosynthetic reinforced pile-supported embankment with piles arranged in triangle has been studied based on the concentric circular soil arching model with introduced concept of the equivalent pile cap. First, it is assumed that the soil arching is composed of concentric hemispherical soil arching formed by three piles and concentric semicircular soil arching formed between adjacent piles. The load transfer of 3D concentric spherical soil arching and 2D concentric circular soil arching is considered, based on which the soil arching effect has been analyzed. Then the tensioned membrane area of each pile was divided into six parts, and the load transfer of the reinforced material caused by the overlying fill was calculated according to the hypothetical parabolic settlement of the reinforced material. Finally, the computing method of load transfer efficiency of geosynthetic reinforced pile-supported embankment with triangular pile pattern is deduced by jointly analyzing the soil arching effect and tensioned membrane effect, along with introducing the coefficient ? to ensure the overall vertical stress balance. The validity of the proposed method was verified through a comparative analysis of the existing literature data. It is shown that the calculation results of the proposed method are close to the actual engineering data, which can provide a theoretical reference for engineering practice.

There is a strong coupling effect between horizontal and vertical direction during inclined drawing of spiral anchor, but its coupling mechanism is not clear yet and lack of quantitative evaluation basis. Circular anchor plate is used to model the single blade screw anchor to carry out inclined drawing model tests in medium-density sand. The inclined drawing bearing mechanism and the influence law of various factors of the flat circular anchor are deeply revealed through the self-made transparent test chamber and digital photographic measurement technology. Some main conclusions are obtained based on the tests. The symmetry of the displacement field and the shear strain field of the soil around the anchor can be divided into two development stages with the change of the load angle. The influence of buried depth ratio on the symmetrical shape of displacement field is more significant than that on shear strain field. With the decrease of load angle, the movement mode of soil around the anchor is gradually transformed from the vertical movement mode in vertical drawing to the rotary movement mode in horizontal drawing, while the two modes coexist in inclined drawing. With the decrease of load angle, the pulling load-bearing displacement curve is transformed from softening type to hardening type. The larger the load angle and buried depth ratio are, the more significant the oscillation of load displacement curve is. Under different buried depth ratios, the three intervals of bearing capacity growth curve have distinct characteristics, which can be fitted by three-stage first-order function. The control degree parameter Cd can reflect the evolution of the control direction with the load angle. When the load angle is in the range of [0°, 80°], the horizontal direction controls the load-bearing characteristics of inclined drawing, while the section of [80°, 90°] is controlled by vertical drawing. The vertical drawing action can significantly improve the horizontal load-bearing capacity of the flat anchors. When judging the load-bearing limit state of the inclined drawing plate anchor or screw anchor, the control direction of the uplift behavior should be determined first.

The Brazilian test was conducted on sandstones containing vertical and horizontal laminations after 25 ℃ to 1 000 ℃ treatment. Digital imaging correlation (DIC) was used to record the evolution of the horizontal strain field of high-temperature bedding sandstone during the splitting process. Meanwhile, microscopic structural damage characteristics of samples after different temperatures treatment were investigated using scanning electron microscopy (SEM). The results show that: (1) The strain concentration of the bedding sandstone before splitting can be divided into two types: the strain concentration at both ends of the disk (≤400 ℃) and the strain concentration at the center of the disk (>400 ℃). (2) With the increase of temperature, the tensile strength of vertical and horizontal bedding sandstone first increases and then decreases and reaches the maximum at 200 ℃. With the increase of temperature at 600~1 000 ℃, the effect of bedding on the tensile strength gradually decreases. Temperature becomes the main factor affecting the tensile strength after a threshold temperature of 800~1 000 ℃. (3) The microstructure damage analysis shows that the sandstone matrix is mainly characterized by increased cracks and extended length after the lower temperature treatment, while the crystal is still intact. Also, after this treatment, both the number and size of pores in the bedding plane increase and more damage in bedding occurs. However, when the temperature is higher, the damage of matrix and bedding is very similar, which is the main reason for the variations in strain and strength of the sample after heat treatment.

Based on the limit equilibrium method, stability analyses of the reinforced multi-tiered wall are conducted to calculate the required strength of geosynthetics. The available reinforcement tensile capacity against the front and rear-end pullout is used to determine the distribution of the required strength and the strength of connection to the facing for each layer. The calculated solutions are compared with the results obtained from the experiments or numerical simulations for the verification of the presented method. A series of parametric study is carried out to investigate their influences on the stability of reinforced multi-tiered wall and its critical failure surface. Several conclusions are drawn from the results. Compared with the calculated results of this study, the active earth pressure theory recommended by FHWA could conservatively estimate the stability of the multi-tiered wall. The composite failures due to the insufficient reinforcement length can be avoided by increasing offset distance and number of tiers. The connection strength can suddenly increase at the step and then the bottom facing block should be embedded at a deep depth to prevent the connection damage. The critical offset distance is 0.7-0.8 times of the height of the lower wall judging from the critical failure surface, but the value determined by the distribution of reinforcement tensile strength is consistent with that of FHWA.

In order to investigate the mechanical properties of Zhanjiang structured clay in the three-dimensional stress state and the influence of structure on its strength criterion, a series of undrained true triaxial tests of different intermediate principal stress ratios, b-values, with equal mean principal stress, p-values, and undrained plane strain tests was carried out. The results are as follows. When p is less than or greater than the yield stress of the structure, the q- curves are strain softening and mild strain hardening type in general. The q- curves of true triaxial tests with different b-values are similar in shape. As b-value increases, the large principal strain corresponding to the q peak point shows the decreasing trend. Under different b-values, the effective cohesion decreases with increasing b-values, while the effective friction angle increases with increasing b-values. The effective cohesion and friction angle for the plane strain compression tests are between the effective cohesion and friction angle corresponding to b=0.25 and b=0.50. Influenced by the structure of clay, the strength criterion on π plane is applicable to the Lade-Duncan criterion when p-values are less than the yield stress of structure, while it is more applicable to the generalized nonlinear strength theory based on Mises criterion and Lade-Duncan criterion when p-values are greater than the yield stress of structure. For plane strain tests, the b-values of Zhanjiang clay under plane strain loading and unloading conditions are between 0.18 and 0.29 at failure, and the strength at failure can be approximated by the generalized plane strain strength criterion based on the general Mises and Lade-Duncan plane strain strength criterion.

With the rapid development of mountainous highways and high-speed railways in China, geological disasters caused by new tunnel excavation, such as landslides, are widespread. Meanwhile, the diseases caused by landslides in existing tunnels are also increasing, resulting in significant harm to the tunnel construction and operation. In this paper, the academic research status, existing problems, and the development prospects associated with the tunnel-landslide system were summarily all over the world. First, the relative spatial location relationship and deformation characteristics of the tunnel-landslide system were systematically investigated. Second, the detailed analyses of the current status and prospects of research on tunnel-landslide interaction from five aspects geological survey, theory, model test, numerical simulation and field monitoring. Then, the control and protection techniques of the tunnel-landslide interaction were expounded from landslide reinforcement, tunnel reinforcement, and monitoring and prediction technology, and the corresponding shortcomings in the existing research and the aspects that still need to be discussed were marked. Finally, it is recommended to carry out further research on the landslide soil plasticity, nonlinear contact, earthquake and rainfall multi-factor coupling effects, the development and utilization of centrifugal model tests, the applicability of constitutive models, and the fine modeling of tunnels. Also, the impact zones of tunnel excavation should be further optimized, and the corresponding novel control and protection technologies should be developed. On this basis, a new type of monitoring technology system linked and shared for tunnel-landslide can be thus established. This paper provides new perspectives and essential data for academic research on tunnel-landslide system engineering.

Rayleigh waves in layered half spaces are dispersive, and the excitabilities of Rayleigh waves are varied at different frequencies. When a cavity full of air is present in the underlying half space, the incident Raleigh waves are scattered at the cavity. In this paper, the waves in the layered plates are studied using the plates with the layer properties and thicknesses equal to those over the cavity. Effects of the ratio of buried depth (plate thickness) to wavelength on differences between the dispersion curves of the diffracted and Rayleigh waves are analyzed. The dispersion of the diffracted waves is obtained from the spectrum of synthetic responses over the cavity in the frequency-phase velocity domain. The dominant diffracted waves are identified by comparing the dispersion curves of the diffracted waves and the plate waves. It is shown from the results that the behavior of the dominant diffracted waves is similar to that of the fundamental plate waves; for the incidence of Rayleigh waves with the wavelength longer than the buried depth, the phase velocity of the diffracted waves is slower than that of Rayleigh waves; with the wavelength of incident Rayleigh waves decreases, the phase velocity of diffracted waves gradually approaches that of Rayleigh waves. Compared with the displacement structure of Rayleigh waves, the variation of the diffracted wave displacement with the depth is flatter. This variation is related to the layer structure and frequency. Due to the displacement structure of the diffracted waves, the vibration energy at the surface is reduced. The level of reduction is varied at different frequency components. This phenomenon is a major feature of the spectral disturbances caused by the presence of a cavity. The locations of a cavity can be identified from the spectral disturbances in the offset-frequency domain.

Finite element method (FEM) is the most widely used numerical analysis method, which is an effective solution to all kinds of engineering and scientific problems. However, the interpolation based on shape function often does not have desired accuracy in cases where the internal field variables of the finite element need to be solved. To deal with this kind of problems, a high-precision solution is proposed, and the basic idea of the solution is the combination of finite element and Taylor expansion. The value of internal field is obtained by establishing and solving linear equations of unknown field variables in the element with respect to known field values at element nodes. The coefficients of each equation depend on the relative position of the points. The results illustrate that the proposed method, which implement a relatively simple algorithm, is applicable to multi-dimension and multi-order elements. It also shows an excellent performance in the application of nonlinear and high-order field functions. This new solution algorithm with high computational efficiency and high precision is expected to serve the intermediate steps of nonlinear computation and satisfy the requirements of high precision post-processing. The method is not limited to FEM and can be extended to all kinds of discrete numerical methods including meshless method.

Based on the establishment of peridynamic nonlocal porous media seepage model, several kernel functions reflecting the degree of nonlocal effect are introduced to improve the calculation accuracy, and the peridynamic permeability coefficients corresponding to different kernel functions are derived. In the two-dimensional seepage model, the Weibull-distributed permeability coefficient model and the fracture network seepage model are established to realize the heterogeneous seepage in porous media matrix and fracture, respectively, which make up for the shortage of classical peridynamic model that cannot well simulate the heterogeneous seepage in porous media such as rock and soil. Different kernel function models are tested in simulating one-dimensional seepage problem, and the influence of kernel functions on simulation result is analyzed. The results show that the improved model can well converge to the theoretical solution, and the polynomial kernel function has the highest convergence accuracy relative to other kernel functions. Then, the polynomial kernel function is introduced into the two-dimensional model, and the corresponding two-dimensional permeability coefficient is derived. The proposed heterogeneous seepage model is employed in the simulation of two-dimensional seepage in porous media with and without fracture, and the results show that the proposed model can well simulate the heterogeneous seepage process in rock materials. Therefore, the proposed heterogeneous seepage model has wide application prospect in porous media seepage simulation.

In the reliability analysis of slope stability, the deterministic analysis method is usually used to calculate the safety factor to evaluate the stability of slope. However, the inherent spatial variability of rock mass properties cannot be considered and described adequately in traditional deterministic method, resulting in the inaccurate calculation of slope failure probability. Based on Hoek-Brown criterion and random finite difference method (RFDM), the reliability analysis of slope stability and random response of pile are discussed in this paper considering spatial variability of rock mass. The uniaxial compressive strength and material constant for the intact rock are regarded as random field variables and geological strength index GSI is assumed to be a random variable. The results show that the spatial variability of rock mass parameters has a significant effect on slope failure probability and pile response. Ignoring the spatial variability of rock mass parameters will overestimate slope failure probability and the mean value of the maximum bending moment of anti-slide pile, and underestimate the mean value of displacement at pile head. The results can provide design guidance for slope reinforcement as well as layout optimization of anti-sliding piles.

Based on the Biot theory of porous media, this paper proposes a coupled vehicle-track-saturated foundation model to study the dynamic responses of saturated soft soil foundation under high speed train via two-and-half dimensional finite element method (2.5D FEM). It is found that the ratio of train speed c and soil Darcy permeability ( ) determines the extent to which maximum excess pore pressures build up in saturated soft soil under the train load when the load speed is lower than the critical speed. For a saturated soil of a particular stiffness, if is less than or equal to 3×104, the soil can be viewed as highly permeable in relation to the load velocity and almost no excess pore pressure is developed, the saturated soil can be modeled using single-phase medium. There is a critical value of for the development of excess pore pressure, when is smaller than the critical value, the maximum excess pore pressure increases with increasing . Above the critical value of , the maximum excess pore pressure remain independent of . The amplitude and affect scope of effective stress are mainly controlled by train speed and soil permeability for saturated soft soil foundation. The response of displacement is mainly controlled by the train speed. Significant Mach effects have been induced in the saturated soil foundation by the moving train, when the train speed reaches or exceeds the critical velocity of the track-foundation system.

The Shah and Heaviside step functions are used to describe the dynamic excitation of the vibratory roller, and the dynamic response analysis of the double-layer foundation with the upper layer of unsaturated soil and the lower layer of saturated soil is carried out. The three-dimensional Fourier transform is used to solve the dynamic control equations of saturated and unsaturated soils, and the dynamic response solution of the double-layer foundation in the transform domain is derived. Through the analysis of numerical examples, the dynamic response of the double-layer foundation under the action of the vibratory roller and the influence of parameters are studied. The results show that the vibration peak value of the foundation will increase accordingly as the excitation frequency and nominal amplitude of the roller increase. When the speed of the road roller exceeds 5 km/h, the vibration peak value of the foundation gradually increases accompanied by fluctuation. The amplitude of the fluctuation depends on the excitation frequency of the road roller. In addition, this paper also considers the influence of saturation on soil shear modulus and permeability coefficient. The study also found that the soil has greater dynamic stiffness and the vibration displacement of the foundation decreases when the saturation is in the range of Sw0~1-Sw0.

Seepage erosion can lead to the loss of particles in the soil with water flow, thereby changing the mechanical and hydraulic properties of the soil, and then causing the deformation and even damage of earth-rock dams in engineering. In this paper, the coupled CFD-DEM method is used to study the seepage erosion characteristics of gap-graded sandy soil, which is widely found in dam foundation, filter-base soil systems in earth-rock dams and gravel packing for sand control in oil and gas production, after reasonable simplification of its gradation. The effects of hydraulic gradient, confining pressure and fines content on seepage erosion in gap-graded sand soils were investigated through 8 groups of upward seepage simulation. Macroscopic phenomena such as the mass of fines loss, fines loss rate, soil surface settlement and microstructural changes were monitored in the tests and verified against previous indoor tests. The results showed that the effect of fines content on the mass of fines loss, peak fines loss rate and soil surface displacement from the numerical simulation was more significant than the effect of the confining pressure and hydraulic gradient in the tests. In addition, the analysis of microstructure demonstrated that the conversion of the soil force chain transfer structure occurred near the threshold of 25% fines content. The triaxial results indicated that the loss of fines also led to a decrease in peak strength and E50 modulu of soil.