International Journal of Geomechanics

This study aims to investigate the failure mechanism of structural support systems in braced excavations. The three-dimensional finite-element method (FEM) was used to model the complexity of real geometry by considering the elastoplastic structural support system. Because failure could occur at the connection between walls and struts, a new model of a strut–wall connection was considered in the analysis to represent the actual condition of excavation failure. Three failure case histories were studied to investigate the performance of strut–wall connections by calibrating their strength parameters until the factor of safety was close to unity. It was found that a good result of stability analysis could be obtained in the FEM by considering this model. The yielding of the strut–wall connection model initiated the collapse of the bracing system in all case histories, followed by the yield of struts and failure of soils. A robust failure mechanism was also obtained, in which the yielding of the structural support system at failure initially developed at the middle section toward the corner of excavation geometry.

This study numerically investigates the undrained bearing capacity of circular foundations founded on a two-layered clay under combined loading of vertical, horizontal, and moment loads using three-dimensional finite-element analysis. Each clay layer has different thicknesses and shear strengths, and two types of foundation–subsoil interface are considered: an interface with (a) zero tensile capacity or (b) nonzero tensile capacity. Analysis results are presented in the form of normalized failure envelopes for a wide range of layer thicknesses and shear strength ratios. The presented normalized failure envelopes under combined loads with or without the interface tension can be considered as graphical solutions for circular foundations on a two-layered clay in offshore marine environments. Failure mechanisms under various combined loads provide further insights into foundation-layered soil interactions.

Weak interlayers determine the strength and stability of a jointed rock mass. The influence of weak interlayer filling state on the shear strength and failure patterns of a rock mass was studied by direct shear testing. Two different shear failure patterns of infilled joints were discovered, depending on the filling conditions of the weak interlayer. Shear failure occurred within the weak interlayer for large filling thickness, while the coupling effects of occlusal failure of asperities and shear failure of weak interlayer occurred for thin filling thickness. The shear strength of the infilled rock mass depended on the shear strength of weak interlayers and the occlusal strength of asperities on the rough joints. Moreover, the shear strength of a weak interlayer was entirely utilized in the first stage of shearing, and the occlusal strength of asperities then became much important with increasing shear deformation. The Mohr–Coulomb criterion was adopted to study the relationship between the peak stress and the normal stress in the first and third stages of shear stress evolution, which confirmed that the apparent cohesion and internal friction angle severally controlled the shear strength of the rock mass under low and high normal stresses. Finally, the impact of filling thickness on the shear strength of a jointed rock mass was predicted, according to the variations of apparent cohesion and internal friction angles. Observable shear displacement, accompanied by the secondary growth of shear stress, may be generated in an infilled rock mass before catastrophic failure. The results were of great significance for understanding the influence of the weak interlayer filling state on the shear strength and failure patterns of a jointed rock mass. Monitoring the stress and deformation of the infilled rock mass could provide useful information for the prediction of engineering disasters in rock, allowing effective control measures to be taken before hazards occur.

Analytical method has many merits over numerical iteration procedures in calculating the lateral bearing capacity of rigid single pile due to high efficiency and low computational cost. With consideration of the complexity of pile–soil interaction, the current analytical method may ignore the influence of the shaft-resisting moment, lateral force, and moment at the pile tip, leading to inaccuracy. In this paper, a simplified analytical method considering all soil reactions was proposed to predict the lateral bearing capacity of rigid single piles in sand. To be specific, the proposed models can estimate the variations of the shaft-resisting moment, lateral force, and moment at the pile tip with horizontal displacement. The derivative procedure of establishing force and moment equilibrium was illustrated by three cases; herein, the lateral bearing capacity of rigid single piles was obtained. The simplified method is validated by full-scale measurements. Based on the verified analytical solution, a parametric analysis is carried out to explore the influential factors (e.g., internal friction angle and pile diameter) of the lateral bearing capacity of rigid single piles.

Mechanical properties of rock are affected by the specimen slenderness ratios. However, the temperature-dependent nature of rock with different slenderness ratios have not been investigated. To better understand the relationship of slenderness rations and temperature, marble specimens with four slenderness ratios are used to perform uniaxial compressive test after exposure to four different treatment temperatures. Elastic modulus first increases as slenderness ratio increases from 0.5 to 2, followed by a drop as it increases to 4. Peak strain slightly increases with the increase in the treatment temperature. All specimens exhibit a brittle failure, and the brittleness is more pronounced for those with larger slenderness ratios, while the rising treatment temperature changes the rock failure from brittle to slightly ductile. Rock strength decreases as the specimen slenderness ratio increases. A new correction equation accounting for the treatment temperature is proposed to evaluate uniaxial compressive strength. Four failure modes of the rock are observed, including cone-shaped, splitting, shearing, and mixed. The influence of slenderness ratio on rock strength may be associated with the stress difference inside the specimen, and the thermal damage mechanisms can be attributed to dehydration and chemical actions and nonuniform expansion and shrinkage of minerals during the process of heating and cooling.

Carbonate sand has been widely used as the building materials for land reclamation in marine areas in the recent decades. The complex inner structures and particle characteristics of carbonate sand increase the difficulty and complexity in foundation treatment. In this study, the particle breakage and ultimate state of binary carbonate sands with different small-grain contents and size ratios were investigated through impact loading tests. The results showed that the particle breakage and ultimate state are influenced by the small-grain content and size ratio. The breakage of the carbonate sands shows significant differences for different small-grain contents due to the fabric state varies between a coarse-sand-dominated state and a finer-sand-dominated state except for the size ratio of 1.92 where the effect of small-grain content is negligible. A hyperbolic function was proposed to establish the relationship between the input work and particle breakage. The evolution of the particle size distribution of the sand with the size ratio of 1.92 under impact loading follows a monofractal pattern as the uniformly graded soil behaves. The multifractal or bimodal phenomenon becomes more obvious when the size ratio increases. The particle shape, size effect, and coordination number on the fabric of the binary carbonate sand could affect the particle breakage and ultimate state of the specimens.

To investigate the responses of inclined loaded piles in layered foundations, this paper proposes a generalized solution based on the principle of minimum potential energy. First, the energy equations for an inclined loaded pile and the surrounding soil are deduced. With the consideration of deformation compatibility and the pile–soil interaction, the governing differential equation for the pile is obtained via a power series method based on the energy method. Subsequently, the power series solutions for the pile deformation under axial and lateral loads are obtained. The results indicate that the analytical solution proposed in this study can provide consistent predictions with experimental results. Furthermore, the ratio of the elastic modulus between the upper and the lower soil, the length–diameter ratio, and the change ratio of the elastic modulus of the adjacent soil have significant influence on the lateral displacement and the bending moment of the inclined loaded pile.

The main causes of soil setup effects on pile response are generation of excess pore water pressure (EPWP) due to installation of prefabricated piles in saturated soils and subsequent dissipation of EPWP and, hence, stress state variations around the pile shaft. The main objective of this paper is evaluating the effects of pile diameter and over-consolidation ratio (OCR) on variations of stress state in soil adjacent to the pile and variations of the pile ultimate load over time using a nonlinear finite-element method numerical scheme and comparisons with field test data. The numerical model involves simulation of the pile penetration throughout the installation process and, hence, simulation of EPWP inducement and its dissipation over time during consolidation. The field data include pile driving and load test data in normally consolidated (soft) and overconsolidated (stiff to very stiff) fine-grained strata. The results have shown that the ratio of EPWP dissipation to overconsolidation stress reduces with an increase of OCR. The coefficient of lateral soil pressure has also increased with OCR and pile diameter. A “setup ratio” is defined as the ratio of shaft resistance at the end-of-consolidation to end-of-drive and is shown to have a proportional relationship with the pile diameter and a nonlinear and reducing trend with an increase in OCR. Correlations are proposed to modify existing relations for an increase in shaft resistance with time, incorporating OCR and pile diameter as well. Finally, the field data interpretations of a site having sufficient pile-load testing data in normally and overconsolidated fine-grained stratifications have validated the findings of the numerical model.

A uniaxial strain-softening constitutive model for fiber-reinforced soils is developed based on the disturbed state concept (DSC). The response in the relatively intact state is assumed to satisfy the Duncan–Chang model obtained from the prepeak stress–strain curve, while the fully adjusted state response satisfies the linear model obtained by an extension of the residual strength. The apparent stress–strain curve is a weighted average response derived from the two aforementioned response curves by a disturbance function that acts as the weight. The peak of the stress–strain curve and the postpeak stable point are assumed as the starting and ending points of the disturbance, respectively, which assign a reasonable physical sense to the parameters in the disturbance function. Comparisons of stress–strain curves and peak strength reveal that for a specified fiber, fiber content exhibits a greater influence on the reinforcement effect than fiber length. Five required parameters that vary with fiber content are used in the DSC model. Five sets of uniaxial compression test data of different fiber-reinforced soils are evaluated, and a high consistency between the stress–strain curves predicted by the DSC model and the test curves is noted. Both the consistency index δ and the energy absorption capacity reveal a satisfactory description of the fiber reinforcement effect.

A concrete-filled steel tubular (CFT) yieldable support is proposed as a new passive support system in deep tunnels to improve the stability of soft rock mass, which consists of a CFT arc, a porous metal connector, and a steel tube. The connector provides a new yieldable mechanism; that is, the constant yield resistance and large deformation under compression can be determined by the void ratio and porous length of the connector. The test results indicate that the load–displacement response for the CFT yieldable support can be divided into four stages, namely, elastic stage, yieldable stage I, load transition stage, and yieldable stage II. A numerical model is then developed to investigate the deformation of a deep tunnel supported by the CFT supporting system. The results indicate that a higher concrete strength can lead to a lower deformation of the CFT yieldable support. The deformation of the tunnel roof can be effectively controlled by using higher-strength concrete. The void ratio obviously influences the deformation of the roof, and a higher void ratio tends to lead to a larger deformation. Finally, an empirical approach is suggested to predict the initial resistance and bearing capacity of the CFT yieldable support.

Three-dimensional finite-element models were developed and validated employing the published results from a comparative shaking table testing program of identical four-pile groups installed in saturated and dry sands. The validated models were used to analyze the seismic lateral and axial responses of helical piles to investigate the soil–helical pile–superstructure interaction. The analysis results demonstrated that the lateral displacements of the helical piles and adjacent soil decreased compared with those of the conventional straight shaft piles. In the saturated soil tests, the maximum bending moments occurred at the interface of the layers, while they occurred at the pile top in the dry tests. The stresses and strains in the helices were higher in the dry tests than in the saturated tests and were less in the double-helical pile helices than in the single-helical pile helix. The end-bearing force increased as the ground motion intensity increased in the dry tests, while it decreased in the saturated tests due to the development of high excess pore pressure in the bearing stratum. As liquefaction occurred, the shaft resistance of the helical piles diminished and the pile settled. However, the higher end-bearing force was mobilized, which compensated for the decrease in the shaft force. This observation demonstrated the excellent performance of helical piles in maintaining their capacity during and after liquefaction and controlling the postliquefaction settlement. The second helix further reduced the helical pile settlement but had a negligible effect on the lateral displacement. Finally, the response of the helical pile groups in the saturated test was dominated by rocking behavior, while flexural behavior dominated the response in the dry tests.

Although many calculation methods for tunnel face support pressure have been proposed, they are difficult to use in practical applications. In tunneling, the tunnel support pressure is currently being determined by empirical methods. In this study, five special geological sections were selected based on the shield tunnel project between Wangfujing and Qianmen Stations of Beijing Metro Line 8 to evaluate the different support pressure ratios λ by using the particle flow code (PFC). Both the stress distribution in the ground and the settlement under different support states were analyzed. A simplified limit-equilibrium method was developed in combination with the limit state in the PFC model. The present method was compared with the classical limit-equilibrium calculation methods to predict the active limit support pressure in the tunnel face. The values of the minimum limit support pressure ratio λ_min of the tunnel face were suggested. The results showed that such ratio should be set to 0.6–0.7, which implies that the change in the support pressure cannot be less than 0.6 times of the true strata stress before excavation. The present calculation method of the limit support pressure is simple and effective and can be used in the design and construction of shield tunnel engineering.

This paper presents an investigation on the microstructural evolution alongside the strength degradation of the soft marine soil under T-bar cyclic penetration. The marine soil that was recovered from the seabed in deep-water areas in the South China Sea can be representative of the characteristics of typical soft marine clay in this water area. The microstructure of clayed soils is characterized by particle-constituted aggregates and interaggregate pores, which is commonly considered to predominate the strength of soils. To quantitatively capture the evolving microstructural characteristics of the soil during loading, a new indicator (i.e., probability entropy, H) is proposed based on statistics of the alteration in aggregate size and orientation of the soil. With the aid of the new indicator, the soil microstructural evolution is further evaluated and associated with strength degradation during the continuous T-bar cyclic loading course. In addition, through a comparison between the intact marine soil samples and reconstituted ones, the effect of microstructural cementation of marine soil is examined on the shearing strength during the cyclic loading. The two types of soil samples show a significantly different evolving trend of microstructure. The probability entropy of intact soil decreases, while that of reconstituted soil increases. Thus, the intact soil exhibits a higher probability degree of entropy change than does the reconstituted soil. This result may provide a plausible explanation for the difference in strength between the intact soils and reconstituted ones, even if they have been subjected to the same consolidation stress condition. The novel quantitative method to evaluate the soil microstructure can be further applied to understand the mechanism of strength degradation of soft marine soils. This will provide a deeper insight to the engineering properties of those marine soils, which will facilitate a precise design for practical offshore foundations in deep waters.

The application of load-transferring mechanism is significant in the design of rigid pile–net composite foundations. A three-dimensional (3D) analytical model is adopted in this paper to analyze the load-transferring mechanism for the rigid pile–net composite foundation under the effect of uniform load. The multiple geosynthetic–reinforced cushion layer (MGRCL) is idealized as a typical thin plate with large deflection, and its bending stiffness matrix is also deduced with respect to the coupling effect of the multiple geosynthetic and gravel. Considering the actual 3D stress and displacement boundary conditions, deformation equations are developed for the MGRCL, and the corresponding solutions are also proposed with the consideration of the pile–soil interaction in two phases. A comparison between the analytical solution and the experiment results is performed, validating the accuracy of the proposed analytical method. Furthermore, a parametric study is conducted to investigate the influences of many factors on the load-transferring mechanism of the rigid pile–net composite foundation, including the equivalent modulus of the MGRCL, the stiffness of the soil adjacent the piles, the pile spacing, and the pile diameter. The results indicate that the stress ratio of pile to soil increases with the growth of the equivalent bending stiffness of the MGRCL and the pile spacing, and it decreases with the increase of the stiffness of the surrounding soil and the pile diameter.

Tunneling inevitably induces changes in soil stress and, hence, may adversely affect the surrounding ground and nearby existing tunnels. A model test and a series of numerical analyses were carried out to investigate the response of the ground and existing tunnels in sandy soil to nearby tunneling according to the relative spacing. The test results showed that increasing the distance-to-diameter ratio (d/D) changed the settlement trough from W-shaped to U-shaped along the transverse section. In addition, the major settlement area induced by each advancing step along the longitudinal section was within 0.75D in front of the tunnel face. The numerical results showed that the overall downward movement of the existing tunnel was due to the combined action of soil pressure and excavation unloading. In this article, the mechanism of the W-shaped surface settlement is discussed; a modified Peck formula is used to describe the W-shaped settlement trough, and the relation of typical parameters to d/D is analyzed.

The present study investigates the performance of single fixed-head vertical and batter piles (10° and 20° batter angles) subjected to lateral spreading displacements adopting an integrated approach of multigene genetic programming (MGGP) with design of experiments. Three-dimensional fully coupled numerical analyses are carried out using the pressure dependent multiyield (PDMY02) material model considering variation in permeability of liquefiable soil. The parameters influencing the response of pile foundation (maximum bending moment and pile head displacement) are initially screened using the fractional factorial design approach. Central composite design (CCD) is then adopted to generate the design matrices for conducting detailed numerical analyses. Using the output, prediction models are developed for responses of vertical piles and batter piles (both positive and negative) in laterally spreading soil using MGGP. Further, parametric analyses are conducted to study the influence of various parameters on pile response in laterally spreading soil conditions. Finally, the performances of vertical and batter piles are compared by estimating the reliability index using the Monte Carlo technique.

The conjugated X-type cross joints are one of the main forms of rock mass in nature. It is a composite geological material with macrodefects like joint fissures, and microdefects like microjoints and microvoids. From the perspective of composite damage, an equivalent elastic model considering macro- and microdefects of rock mass is formulated. First, the micro- and macrodamages caused by cross joint and wing crack propagation are used to build a composite damage model of nonpenetrated cross-jointed rock mass based on the strain equivalence principle. Next, considering the interaction between cross joints and the conditions of wing crack propagation, the stress intensity factor at the tips of cross joints before propagation and that at the tips of wing cracks after propagation are derived, respectively. Third, the macrodamage variables involving the geometric characteristics of cross joints and the friction coefficient of joint surface are derived based on fracture mechanics and strain energy theory. Finally, the proposed model is tested on the samples of similar materials in the cross-jointed rock mass; the interference effect between cross joints is analyzed using digital image correlation technology; the calculated results of the model are compared with the experimental results. The model calculation coincides with the test results, proving the rationality of the model. The model helps understanding the influence law of the interference effect of cross joints on the damage and deformation characteristics of rock mass and has guiding significance for related rock mass engineering practice.

During underground mining excavation, dynamic disturbances (e.g., blasting) may accelerate rock creeping and induce unstable failure. It is crucial to properly quantify the impact of dynamic disturbances on creeping behavior to understand the long-term effects of underground excavation on rock media. A damage-based creep model was established in this study and implemented in Fast Lagrangian Analysis of Continua in 3D (FLAC^3D) to quantify the damage and unstable failure of creeping rock triggered by dynamic disturbance. This model reveals the mechanical behavior of rock under creep-impact loading. It was verified by calculating the viscoelastic deformation around circular excavation, by reproducing the damage process under static loading, and by simulating the rock damage and failure under creep-impact loading. The model was then used to examine the mining-induced creep deformation around an operational shaft in Xincheng Gold Mine, China, where both the mining-induced creep of the country rock mass and dynamic disturbance of blast-induced vibration were considered. Numerical simulation indicated that the dynamic disturbance could accelerate the damage of rock under creep stress, which may be an important factor to trigger the accelerating creep of rock, even though the unstable failure of rock lagged behind the dynamic disturbance. The case study on the shaft stability analysis indicated that the dynamic disturbance could accelerate the time-dependent deformation of the shaft, the first dynamic disturbance induced much more shaft deformation, while in long-term creep (e.g., 5 years), the effect of blasting vibration was not significant. The trend and magnitude of shaft deformation agreed with the in situ measurements, which indicates that the numerical simulation could be used to predict the long-term shaft deformation in future.

Pile foundations are often subjected to lateral loadings. By adding steel plates (fins) to the side of the pile, steel fin pile foundations (SFPFs) can improve the lateral load capacity of piles. Existing numerical studies using elastic–perfectly plastic models (e.g., Mohr–Coulomb model) for soil behavior may result in unrealistic load response when modeling soil–pile interaction in dense sand due to the lack of consideration of strain-hardening/softening behavior. In the present study, finite-element analyses were conducted to understand the effect of fin geometry on the lateral load capacity of SFPFs. The prepeak hardening and postpeak softening soil behavior was accounted for by varying soil strength parameters with plastic shear strain based on a modified Mohr–Coulomb model. The developed model was calibrated and validated against well-documented experimental and field tests in the literature. The validated model was subsequently used to conduct a parametric study to understand the effect of fin geometry on the response of SFPFs subjected to lateral loading at the pile head. The behavior of SFPFs at different displacement levels and load levels was studied. The effect of the relative density of soil on the performance of SFPFs was also investigated. Based on the numerical simulation results, the optimal fin width and length values for mobilizing soil resistance were suggested and the underlining mechanisms affecting the efficiency of fins were discussed.

With the actual environments of the joint rock in the bank slope of the Three Gorge Reservoir region (in China) as the background and considering the research concept that the effect of sodium sulfates and the dry–wet (D–W) cycle on rocks as interactive and inseparable, a test plan for D–W cycles was designed to study the D–W cycle damage of the mechanical characteristics and their correlations with the strength properties of sandstone with a Mode-I crack exposed to a sodium sulfate attack. Based on the crack’s propagation radius and a damage variable reflecting a change in porosity, the degree of D–W cycle mechanical degradation was quantitatively analyzed. The mechanical characteristic of sandstone exhibited obvious damage under sodium sulfate attack and D–W cycles, among which the degree of D–W cycle degradation of the K_IC was the greatest, whereas the internal friction angle was relatively the lowest. Meanwhile, apparent consistency was observed between the K_IC and compression, and between the K_IC and tensile strength of specimen exposed to the sodium sulfates attack under D–W cycles. Moreover, an evident corresponding relationship existed among the deterioration damage of the mechanical properties, corresponding ion concentrations dissolved in sodium sulfate solution, and deterioration degree of the physical characteristics of sandstone. Meanwhile, the correlation relationships among physical and mechanical properties, D–W cycle damage degree, and ion concentration were obtained.

Rainfall infiltration causes the collapse of unsaturated embankments due to loss of suction. In this paper, the Barcelona Basic Model (BBM), a constitutive model developed for unsaturated soils, was implemented in Fast Lagrangian Analysis of Continua (FLAC) for simulating the effect of varying rainfall intensities on compacted embankments. It was observed that large vertical deformations occur and considerably high positive pore-water pressures get developed, accounting for the collapse of an embankment. The results also show that rainfall intensity and duration affect the slope stability. A comparison was made between the results obtained using the Mohr–Coulomb model and BBM. It was found that the soil undergoes larger deformations when modeled using BBM as BBM accurately models the loss of suction upon saturation. Reliability analysis of embankment shows that probabilistic analysis provides a better assessment of slope stability rather than the factor of safety and shows that suction and hydraulic conductivity are critical parameters influencing slope reliability for unsaturated soil slope embankments.

Traditionally, the seepage through embankments and other geotechnical structures is estimated using the hydraulic properties of saturated soil. In most cases, the soil is not fully saturated, and the use of saturated soil properties can lead to erroneous results. A reliable assessment of slope stability needs comprehensive characterization of both unsaturated and hydraulic properties of saturated soil. The permeability coefficient of unsaturated soil is usually estimated using existing permeability models derived from the soil water characteristic curve (SWCC) of soil. The performance of these prediction models has not been consistent in the past. A proper determination of unsaturated soil permeability properties will be needed for better stability designs and checks of earth structures. In this study, an experimental program is designed to evaluate the influence of matric suction, net confining stress, and wetting and drying cycles on the hydraulic conductivity of a clayey soil over a wide range of suction values. Modified suction-controlled triaxial equipment was used to apply and maintain suction and hydraulic head in a soil specimen to measure the coefficient of permeability for drying and wetting cycles. Additionally, a series of fully coupled hydromechanic numerical analyses was performed to examine the effect of hydraulic properties of unsaturated soil on pore water pressure response and safety factors of slope for transient seepage conditions during drawdown. The effects of stress-dependent hydraulic properties and hydraulic hysteresis on transient seepage were also investigated. The findings from this study highlight the role of hydraulic properties of partially saturated soil in seepage and slope stability analysis of earthen dams.

Fully grouted rockbolt is a form of reinforcement commonly used in underground projects. Its mechanical behavior is of vital importance to enhancing the stability of surrounding rock masses. To investigate the effect of different loading methods on the mechanical behaviors of rockbolt, the distinct element code PFC^2D was adopted to simulate the pullout test on rockbolt and a compression test on the bolted rock mass, with Hongtoushan Copper Mine as the engineering background. The stress distribution along rockbolt and the maximum pullout capacity were analyzed. The results indicated that the loading method has significant effects on the mechanical behaviors of rockbolt. In the pullout test, the peak stress in the rockbolt always occurs near the free face. As the rock mass is a passive load-bearing component, the cracks and weak intercalations in the rock mass have little effect on the mechanical behaviors of the rockbolt. Meanwhile, as the external load acts directly on the outer end of rockbolt, the effect of the bearing plate cannot be reflected. However, in the compression test on the bolted rock mass, the peak stress in the rockbolt gradually transfers to greater depth. The existence of cracks and weak intercalations have an impact on the mechanical behaviors of the rockbolt. In addition, with increasing size of the bearing plate, the maximum pullout capacity of the rockbolt gradually increases. Comparison of the simulation results showed that the maximum pullout capacity obtained by the pullout test on a rockbolt is higher than that obtained by the compression test on a bolted rock mass. Therefore, appropriate reduction of the maximum pullout capacity obtained by the pullout test is suggested for rockbolt design, and the reduction factor should be in the range of 0.7–0.8.

Pore ice content is crucial in evaluating the mechanical properties of frozen soils. Existing strength criterion models are usually empirical and ignore the influence of pore ice content. By assuming that the critical state shear stress ratio of soil is a function of the stress level, a critical state line of frozen soil is proposed to consider pore ice content. By combining the Mohr–Coulomb (M–C) and Drucker–Prager strength criteria to describe the failure shape characteristics on the deviatoric plane, a new strength criterion is established for complex stress conditions. The proposed model is validated against existing models and measured data in the literature. In addition, the proposed model can uniformly describe the CSL of different types of geotechnical materials and has a clear physical meaning, which may provide a theoretical basis for constitutive models.

The dynamic failure characteristics and fracture process of brittle materials such as rock involves a complex crack propagation process, the underlying mechanics of which is not yet fully understood. At present, the combination of high-speed photography and Digital Image Correlation (DIC) technology is considered to be the most promising and ideal means to observe crack growth and analyze the failure mechanism of rock-like materials. In this work, ultra-high-speed photography is used to investigate the dynamic failure characteristics of fine-grained sandstone, and scanning electron microscope (SEM) is used to investigate the relationship between the mechanical properties and failure law of fine sandstone and strain rate from the micro perspective. Finally, the failure mechanism of the rock is analyzed by combining the DIC technology. It is found that the fine-grained sandstone undergoes five critical moments under impact load, namely, initiation of the first crack, initiation of the second crack, crack penetration, local crushing, and thorough breaking. With the increase of strain rate, the whole failure process of rock specimen is shortened, and the time between two critical moments is shorter and shorter, indicating that the more severe the failure of the rock specimen in a time interval between the critical moments, the shorter the time required for the process, and the less obvious the strain rate effect. The first crack on the rock surface initiates from the direction of the transmission rod. With the increase of the strain rate, the angle between the crack on the rock surface and the axial direction is larger, and the second crack will penetrate the specimen first.

Soil properties are known to have high spatial variability and often fluctuate with depth. The objective of this study was to investigate the effects of using different models to simulate the spatial variability of undrained shear strength (s_u) to calculate the failure probability of an embankment on soft ground. Two-dimensional random fields of s_u were generated based on one Gaussian and two non-Gaussian copulas, with stationary and nonstationary assumptions. Statistical parameters of s_u variation—mean, coefficient of variance, and scale fluctuation (correlation length)—were estimated from simulated and field data. Monte Carlo probabilistic analyses were performed on embankment stability based on both stationary and nonstationary random fields and all copula approaches; results showed more frequent embankment failures at low water levels in the embankment ditch. In particular, the nonstationary random field (s_u increases with depth) simulations more closely reflected real observed data, with higher probabilities of slope failure and lower mean factor of safety than the stationary random field simulations. Additionally, the non-Gaussian copulas provided simulated data that more accurately reflected observed field data, highlighting the importance of copula selection when characterizing soil parameter random fields.

Excavation causes disturbance to the surrounding soil, affecting the soil’s mechanical properties. This study presents a case study to investigate the effect of excavation disturbance on soil properties and pile capacity via in situ tests. A series of multifunctional piezocone tests, multichannel analysis of surface wave tests, and electrical resistivity tomography tests were conducted at three sites of the Taihu tunnel region before and after excavation with different depths. The changes in soil mechanical properties and the pile capacity loss were evaluated using the test results. The results indicated that excavation disturbance decreased the cone tip resistance, sleeve friction, soil resistivity, shear wave velocity, and undrained shear strength. In contrast, the friction ratio and the effective friction angle were not affected. The average cone tip resistance of soils in the excavation disturbance zone was approximately 51%, 46%, and 62% of its initial value at Sites A, B, and C, respectively. The variation in soil properties was only observed within a limited depth below the excavation surface, which is defined as the excavation disturbance zone. The piezocone test successfully identified the depth of the excavation disturbance zone, and the disturbance zone height was approximately 0.42 times the excavation depth. In the disturbance zone, the cone tip resistance and the undrained shear strength of the soil decreased linearly from approximately 90%–0% with increasing depth. Because of excavation disturbance, the axial and lateral capacities of a pile beneath the Taihu tunnel were reduced by about 9% and 50%, respectively.

This study presents the numerical solution for the seismic bearing capacity of embedded strip footing in Hoek–Brown rock mass. The upper-bound solutions are presented by employing the finite-element limit analysis. The influence of various parameters namely, geological strength index (GSI), yield parameter of the rock (m_i), rock strength ratio (σ_ci/γB), embedment depth ratio (d/B), and the horizontal seismic coefficient (k_h) on the seismic bearing capacity factor (N) of strip footing is assessed. The results are presented as design tables and charts for a wide range of parameters. A parametric study is performed and a discussion on the influence of each parameter on the seismic bearing capacity factor is made. The influence of the considered parameters on the failure pattern is highlighted. It is noted that the lateral extent of the failure surface increases with an increase in the depth of embedment which has a positive influence on the seismic bearing capacity of strip footing.

The mechanical behavior and particle breakage of carbonate sand under a simple shear condition are a concern for many engineers. In this study, simple shear tests were carried out under constant-load and constant-volume conditions, and various combinations of relative density and vertical consolidation stress were considered. The results revealed that the crushing of grains can diminish shear strength and inhibit dilatancy. The ultimate state line shifts due to the impact of particle crushing. In addition, there is a unique relationship regardless of relative density between the ratio of volumetric strain at shear strain of 20% to particle breakage and normalized vertical consolidation stress.

Devastating natural hazards induced by the propagation of extremely rapid, flow-like fragmented rocks can be reduced or even avoided by protective structures in the corresponding danger areas. Such barriers are expected to store the mass before it threatens the vulnerable infrastructures. Proper designs are required by calculating the peak impact force of granular flows on the barriers. In this work, a discrete element method (DEM) was validated with a physical experiment. Sixty simulations were carried out using DEM to study the flow regime governing the dynamic response of granular flows against the barrier. Results reveal that the inertial number (I) can demarcate the flow regime into dense and dilute flow. For the dense flows (I < 3), the equation based on the hydrodynamic model is much more efficient. For the dilute flows (I > 3), the Hertz contact method is better at calculating the peak load. The aforementioned findings are expected to be convenient for engineers designing mitigation constructions against flow-like hazards in mountain areas.

A narrow backfill refers to the limited space behind a retaining wall, constructed in front of an existing structure or rock face. It is known that the use of the classical analytical methods, developed for infinite half-spaces, is not appropriate for narrow backfills. In this study, the limit-equilibrium analysis with bilinear planar slip surfaces is employed and a theoretical methodology is proposed for the estimation of the active earth pressure inside a narrow backfill, considering the soil arching effect. The suggested approach can estimate the distribution of vertical, horizontal, and shear stresses everywhere inside the narrow backfill. It is observed that, as expected, the distribution of earth pressure against the retaining wall is curvilinear due to the arching effect. The influence of the backfill width, surcharge pressure, backfill internal friction, wall–soil interface friction, and rock face–soil interface friction on the earth pressure distribution is studied. The proposed methodology provides acceptable results when compared with pre-existing analytical and numerical studies. Therefore, the suggested approach can be used for the analysis of narrow backfill retaining walls.

Natural methane hydrate, as a potential alternative energy source to fossil energy in the 21st century, is found in abundance in deep-water sediments and permafrost regions. During the production of methane gas from these sediments, the dissociation process may induce various changes to the geotechnical properties. Thus, it is important to study the geomechanical behavior of hydrate sediments and simulate the sediment deformation patterns. In this study, the effects of different sediment types on the mechanical properties of hydrate-bearing soils were investigated using multistage triaxial tests, and the methane hydrate critical state (MHCS) soil model was calibrated using an optimization-based technique. The results revealed that: (1) the strain-hardening phenomenon in methane hydrate-bearing sediments varies with the particle sizes of the host sediments; (2) the strengths of methane hydrate-bearing sediments are higher with the host sediments being pure sand, compared with those with clay-added sediments, and the strength is inversely proportional to the clay contents in these sediments; and (3) the multistage triaxial test data were fitted with the MHCS model, which illustrates the combined effects of the abovementioned factors on the model parameters and geomechanical behavior of methane hydrate-bearing sediments.