International Journal of Geomechanics

Loess is one of the problematic soils with a worldwide distribution for its collapsibility. To study structural strength and parameters of collapsible loess, a number of double-oedometer tests on intact and remolded loess specimens, sampled from Xinjiang, western China, at different initial moisture contents were conducted. The collapse potential curve can be divided into three stages, and the curve at each stage represents the change of the loess internal structure during the collapse deformation process. Stage I: loess initial structure transforms into the secondary structure; Stage II: damage to the secondary structure; and Stage III: loess structure has been destroyed. Proceeding from the damage to loess anticompression capabilities resulting from soaking, a model is proposed to evaluate the structural strength and parameters of collapsible loess. The variation of loess structural strength with moisture content and vertical pressure is investigated, and the loess structural parameters under different conditions are determined. The results ought to enable geotechnical engineers to evaluate the structural strength, stability, and water sensitivity of collapsible loess.

The complex nonlinear mechanical behavior of the combined system of rock and coal surrounding mine openings is a major obstacle for excavation, stability, and support design in mining thin coal seams. In this paper, the triaxial compression failure characteristics and mechanical response of sandstone–coal (SC) specimens with different combination angles are determined. In addition, the influence of the anchor bolt on the mechanical properties of SC specimens is also considered. The results show that the mechanical parameters of the SC and sandstone–coal–bolt (SCB) specimens are different from those of other intact rocks and are substantially affected by the angle. The peak axial strain and triaxial compressive strength (TCS) of the specimens decreased with increasing angles. To comprehensively analyze the phase mechanical characteristics of the specimens and the differences between them, we also established the crack initiation stress index (CI) and crack damage stress index (CD) to evaluate the specimen fracture process. The established stress indices CI and CD can accurately describe the roles of the bolt and angle of the SC and SCB specimens. The bolt can enhance the mechanical properties of the SC specimen after reaching the peak load, restrain the development of cracks, and ensure that the specimen maintains integrity. It should be noted that this type of SCB system is in line with the long-term stability of roadway support engineering applications.

The generalized bounding surface model (GBSM) is a fully three-dimensional, time-dependent model for saturated cohesive soils that accounts for both inherent and stress-induced anisotropy, as well as strain softening and the effect of temperature on the material response. The GBSM combines many previous bounding surface models for saturated cohesive soils and enhances their predictive capabilities. In this paper, certain restrictions that are placed on the analytical definition of the bounding surface associated with the GBSM are identified. The manner in which such restrictions manifest themselves and potentially limit the performance of the model are explained. The remedies that have been developed to overcome such shortcomings are described. Numerical simulations and predictions are presented that provide greater insight into different forms of the GBSM as they are used to simulate the drained and undrained response of isotropically and anisotropically consolidated cohesive soils under axisymmetric and true triaxial states of stress.

Conduits, the main channels within a rock mass, can significantly affect the permeability characteristics of rock masses. This paper presents a Stokes–Brinkman–Darcy coupling model to study the permeability characteristics of porous rock masses with conduits. In this model, the Navier–Stokes equation and the Brinkman-extended Darcy equation are adopted to describe the fluid motions in the conduit and porous rock matrix, respectively. The analytical solutions of both the velocity distribution and the equivalent permeability coefficient, which is the average permeability for the complete rock volume, are derived under the stress jump boundary condition for a rock mass with a conduit. The results of the sensitivity analysis show that the equivalent permeability coefficient of the rock mass with a conduit is positively correlated with the permeability of the rock mass, the relative aperture of the conduit, and the porosity and is negatively correlated with the stress jump coefficient; the aperture of the conduit plays a dominant role in the equivalent permeability coefficient. In addition, the analytical solution of the equivalent permeability coefficient is verified by a seepage test.

A coupled hydromechanical solution to undrained spherical cavity expansion problem in unsaturated soil is proposed with an elastoplastic model for unsaturated soil. The mechanical response and hydraulic behavior of soil during expansion are coupled together through a soil–water characteristic curve (SWCC) that evolves with the void ratio. A system of four first-order differential governing equations is derived based on the equilibrium equation, large stain theory and coupled hydromechanical constitutive relationship of soil. The present solution can reduce to unified hardening parameter model based solution under saturated condition, which validates the proposed solution. The effects of overconsolidation ratio and initial suction on expansion responses are explored based on extensive parametric studies. Special attention is paid to investigate the distributions of the principal stresses, suction, and saturated degree of soil around the expanded cavity; the stress trajectory of a representative element at the cavity surface; and cavity pressure–displacement curves. The proposed analytical solution can serve as a theoretical framework for modelling of some fundamental geotechnical problems in unsaturated soils using critical state soil models.

Clinker ash is a byproduct obtained from coal-fired electrical generators. It is a type of recycled granular material with a complex particle shape and large surface roughness. Particle shape descriptors and surface fractal dimensions are effective parameters to quantify sand grain morphologies. A simple image analysis approach is employed to determine the aspect ratio, sphericity, roundness, and convexity of 12 types of clinker ash collected from thermal power plants distributed on the western island of Japan. Compared to the majority of sands with other mineralogical components, clinker ash particles have a smaller aspect ratio, sphericity, and roundness. Under similar test conditions, clinker ash exhibits higher shear resistance than natural sands at the critical state. Critical state friction angles tend to decrease with increasing aspect ratio, sphericity, roundness, and convexity. A decreased aspect ratio, roundness, and convexity enhance the slope and intercept of critical state lines in the void ratio and mean stress plane. The mean regularity, which is the average of four particle shape descriptors, is regarded as an effective index to characterize the shear strength of clinker ash at the critical state. The surface fractal dimension could also be decided from digital image analysis. The results also show that the critical state friction angle is well correlated with the surface fractal dimension for different types of clinker ash. The implication is that a rougher surface texture hinders the rotation, frustration, and interlocking of particles at the critical state, resulting in higher shear resistance.

Earth retaining structures are constructed to withstand lateral pressure from backfill soil and surcharge pressures from the foundations of adjacent structures. Although sands are considered as the most suitable backfill material for retaining walls due to their high permeability, currently the scarcity of this natural material has raised serious environmental concerns. This study will propose the usage of building derived materials (BDM) as a partial replacement for sand as backfill material for the retaining walls. The utilization of this waste material will help to reduce the cost related to the disposal of waste materials, as well as reducing the carbon footprint, therefore making the process eco-friendly and sustainable. Experimental studies will be conducted on a laboratory scale prototype rigid, nonyielding retaining wall, which can rotate about its base to simulate rotational failure conditions. The width of the backfill was 0.35, 0.5, and 0.65H to assess its effect on the variation of earth pressures (H = height of the retaining wall). The experimental results indicate that the earth pressures were not significantly enhanced by the addition of BDM to sand, which suggests that BDM could be used as an effective lightweight backfill. The optimum pressure was obtained by mixing 20% of BDM with red soil. For backfills that had sufficient widths, the failure surfaces had adequate space to fully develop, whereas it had a limited extension in a narrow backfill. An increase in backfill width (b) decreased the rotation of the wall, therefore reducing the probability of rotational failure. Numerical simulations using finite element software PLAXIS 2D are conducted with the experiments to validate the observations. The numerical results suggest good agreement with that of experimental results.

Artificial neural network (ANN), support vector machine (SVM), and Gaussian process regression (GPR) were developed in this study for predicting resilient modulus (M_r) values of cementitously stabilized subgrade soils. A database was developed using laboratory test results on 160 specimens prepared by using four soils stabilized with three cementitious additives, namely, lime (3%, 6%, 9%), CFA (5%, 10%, 15%), and CKD (5%, 10%, 15%). Of these, 120 specimens (development dataset) prepared using three types of soils were used in development, and the remaining 40 specimens (validation dataset) were used in the validation of the developed models. A commercial software, MATLAB, was leveraged to develop three ANN models (radial basis function network/RBFN; a multilayer perceptrons network/MLPN with one hidden layer; and MLPN with two hidden layers); four SVM models (linear, quadratic, cubic, and radial basis function kernels); and three GPR models (rational quadratic, Matérn, and exponential kernels) by using codes written in MATLAB language. The strengths and weaknesses of the developed models were examined by comparing the predicted M_r values with the observed/experimental values with respect to the mean squared error (MSE) values and determination coefficient (R²) values. Through comprehensive comparison among these three types of models, an MLPN model with one hidden layer was determined as the best performing model developed in this study. It can be used to predict M_r of cementitiously stabilized subgrade soils for Level 2 pavement design applications. This model as well as the other models could be refined using an enriched database.

The support pressure at the tunnel face of earth pressure balance (EPB) shield machines is usually assumed to be uniform from the crown to the invert, which is a notable simplification of reality. In this study, the effects of nonuniform soil pressure in the chamber and the dynamic shield excavation process on the face stability are investigated using a three-dimensional (3D) discrete element method (DEM) model. The behavior of the excavation face subjected to different overburden depths and ground conditions is assessed and also compared with previous research. The results show that the limit face pressure and failure zone is overestimated without considering the nonuniform soil pressure in the chamber. When considering the nonuniform soil pressure in the chamber, a partial failure mode is observed in granular soil that is characterized by flow originating at the upper part of the excavation chamber and limited flow ahead of the face. This effect has a nonnegligible influence on face failure mode and the arching effect, especially near the invert, which is in contrast with the findings associated with global failure modes considered in previous studies.

Combined piled raft foundation (CPRF) is an effective solution for supporting high-rise constructions. The traditional design philosophy of CPRF does not consider the capacity of foundation based on combined vertical (V), horizontal (H), and moment (M) load. However, V-M-H load acts on the CPRF system concurrently due to the action of wind, wave, earth pressure, and earthquake loading in addition to gravity loading. In this context, the present investigation deals with the effect of combined V-M-H load interaction on the behavior of CPRF in sand and clay, respectively. The response of CPRF under combined loading is obtained using a 3D finite element analysis. First, validation of the numerical model is performed considering the model test results conducted in Agartala sand and another based on the available field test result of Messeturm Tower in Frankfurt clay obtained from the literature. Further, failure and design envelopes for the validated CPRF system are developed considering V-M-H load in both sand and clay deposits attributing a variety of influential system parameters. Simplified expressions for design lateral and moment capacities are proposed based on multiple linear regression analysis. Finally, the implication in design based on the findings of the present study is illustrated using a prototype case study structure.

The contractive behavior and flow failure in saturated binary granular soils have been studied by many as functions of their physical properties [gradation, mean particle size, fines content (FC), and packing quality] and mean effective stress, stress history, and cyclic stress amplitude. Nevertheless, little is known on the interplays between frame elements and fines in loose saturated geocomposite mixtures and also between virgin and added frame elements under cyclic loading. That knowledge shortfall has lent uncertainty to flow potential and compressibility predictions for saturated sands in their natural and engineered forms. In this paper, 36 cyclic undrained triaxial-compression tests were performed to investigate the cyclic behavior and properties of saturated loose sand–silt–tire-derived ground rubber (GR) mixtures and to determine the effects of the GR and almost nonplastic fines on the rate of pore-water pressure buildup. The complex interplay among the angular sand, fines (silt) and GR solids, and pore spaces of varied shape, size, and rigidity are discussed at a microscale and invoking the framework of two conceptual models, small silt and large silt. The control of FC on liquefaction resistance was found to be dependent on the sand and GR particle sizes. The relatively greater elasticity of GR than sand lends a damping effect to frame elements and further improves the liquefaction resistance through relaxation of skeletal stresses and reduces the chance of contact destruction for sand particles.

Inverted T-type retaining walls are widely used in civil engineering. Classic earth pressure theories cannot accurately predict the failure mechanism of soils behind inverted T-type retaining walls. Under wall translation mode, two failure surfaces are generated from the upper and lower sides of the heel. By using adaptive finite-element limit analysis (AFELA), numerical results show that when the failure surface intersects with the wall stem, a new failure surface occurs due to soil–wall frictional resistance. In this paper, the phenomenon of stress rotation caused by the soil–wall interface friction is investigated. The influence of the third failure surface on the analytical solution is further considered. An extensive parametric analysis is employed to study the effect of the geometric parameters of inverted T-type retaining walls, soil–wall interface frictional angles, and internal frictional angles of backfill on the failure mechanism of backfill. Based on the limit equilibrium analysis method of the horizontal differential layer, a calculation model for active earth pressure against inverted T-type retaining walls under translational displacement modes is established. Compared with previous methods, the present model is suitable for both long heels and short heels and considers the failure mechanism of soils with higher accuracy. In addition, the application point of active thrust and distribution of earth pressure are provided as references for wall design.

In this paper, the lateral load-carrying behavior of inclined micropiles installed in various soil–rock layer conditions was investigated based on the results from the model load tests and finite-element analyses. The effects of micropile inclination angle, load direction, and rock-embedded ratio were considered in the study. Improved load-carrying behavior was obtained from negatively inclined micropiles in rock with the load direction of 0°, whereas it was disadvantageous for the load directions of 90° and 180°. The lateral load capacity of micropiles for the mixed layer condition increased with a rock-embedded ratio and became larger at a higher inclination angle. Marked increases in the lateral load capacity were observed for rock-embedded ratios larger than 0.8, below which the increases were moderate. The inclination and rock-embedded conditions of micropiles were both adequate to enhance the lateral load-carrying behavior of micropiles, whereas the effect of the rock-embedded condition was less beneficial unless largely embedded. It was also indicated that the maximum benefit of micropiles embedded in rock could be achieved by further reinforcing the stiffness in the upper part of micropiles within the soil layer. It was confirmed that the previously proposed method to estimate the lateral load capacity of inclined micropiles in the sand could be effectively used for the case in rock and the mixed soil–rock layer condition for practical purposes.

Compared to the Rankine and Coulomb passive earth pressure theories, the logarithmic spiral theory considers curved failure surfaces, which is its greatest advantage. To improve the logarithmic spiral theory further, a new numerical method coupled with the Rankine and Coulomb theories was proposed and applied to determine the passive earth pressure coefficient of a sloping cohesive backfill under uniform surcharge loading. The method could yield either convex or concave failure surfaces, and the shape of the concave failure surface was assumed to be a logarithmic spiral. The Rankine and Coulomb theories were employed to determine the failure surface shape and distinguish convex and concave failure surfaces, respectively. Furthermore, approximate passive earth pressure coefficient equations for coefficients K_pγ, K_pq, and K_pc were proposed that consider the coupling effect of the soil weight, vertical surcharge loading, and cohesion. The predictions with the proposed method were compared to those reported by other authors.

The pore-water status, including adsorptive and capillary water, in expansive clay with different dry densities was investigated under the effect of temperature and saline solution via the nuclear magnetic resonance technique. Combined with a method of distinguishing the adsorptive and capillary water, the variations in the adsorptive water content with the thermochemical effect were obtained quantitatively. The experimental results show that the adsorptive water content decreases as the temperature increases, consistent with the theoretical conclusion, which is considered to be attributed to the increase of the chemical potential and the activity of the pore water. On the other hand, the volume of micropores decreases while the volume of macropores increases with the increasing temperature or concentration, resulting from the flocculation and agglomeration of soil particles. Meanwhile, the increase of salt concentration can suppress the electric double layer and decrease the micropore volume, resulting in a decrease in the adsorptive water content. In addition, due to ion hydration, the relaxation of water molecules accelerates, shifting the water distribution curves of soil leftward as concentration increases. This effect overshadows the suppression of electric double layers and the decrease of the micropores, rendering higher adsorptive water content. The microstructure and the pore size distribution, obtained by the scanning electron microscope and mercury intrusion porosimetry experiments, were used to validate the variation of the adsorptive and capillary water in the pores.

Geodisasters associated with fluidized geomaterials, such as flow-like landslides, flow slides, and debris flows, pose a tremendous threat to communities and the environment. Protective structural measures are therefore important for disaster prevention and mitigation. However, the development of a numerical method to study fluid–structure interaction (FSI) remains a challenge. A coupled method is proposed using moving particle simulation (MPS) to simulate the large deformation of fluidized geomaterials and a finite-element method (FEM) to model the dynamic behavior of structures. A new boundary condition based on the Shepard filter method is developed for MPS to improve its efficiency. An interaction model with weak coupling schemes is used to effectively communicate information and coordinate the different time steps between the MPS and FEM approaches. The effectiveness and accuracy of the hybrid numerical method for FSI are verified and validated using a series of benchmark problems.

Helical piles are currently used to support large compressive loads, which requires accurate evaluation of their bearing capacity. High strain dynamic load testing is increasingly used to determine the capacity of helical piles. However, the load-transfer mechanism of helical piles under impact loading has never been thoroughly examined. In this study, the load-transfer mechanism and the interpreted ultimate bearing capacity at 12%, 10%, 8%, and 5% of helix-diameter failure criteria of helical piles installed in cohesionless and cohesive soils under both axial static and impact dynamic loading are investigated numerically. Three-dimensional nonlinear finite element models are developed and verified against two case studies. The verified models are employed to conduct a parametric study covering a range of helical pile configurations. The results showed that the load-transfer mechanism depends on the spacing ratio and the selected failure criteria. Furthermore, the limit equilibrium method overestimates and underestimates the bearing capacity for helical piles installed in cohesionless and cohesive soils, respectively, compared with the numerically predicted values.

In this study, the axial and lateral load-carrying behavior of encased micropile (MP) with perforated configuration was investigated. The perforated casing adopted in this study was a casing with holes on the casing surface to increase the frictional and bending resistances. Experimental tests and finite-element (FE) analyses were performed to characterize the interface friction and the effect of the perforated casing, considering the inclined condition of MP. The experimental tests showed that the interface friction angle of the perforated casing was close to the sand friction angle, whereas that of the smooth-surface casing was nearly half of the sand friction angle. The frictional characteristics of the smooth and perforated casings obtained from the experimental tests were used in the FE analysis. The perforated casing was sufficiently effective to maintain the reinforcing effect of the casing on the lateral load capacity. The axial load capacity of MP with the perforated casing was 22.4% higher than that with the conventional smooth casing. A similar improvement was observed for inclined MPs. It was indicated that the perforated casing was beneficial for both axial and lateral loading capacities.

The reinforcement of shield tunnels with secondary linings is a widely used method to enhance the overall rigidity of tunnels; therefore, ensuring tunnel safety during construction and operational periods. According to a new composite curved Euler beam theory, an analytical method will be proposed to analyze a shield tunnel that is reinforced by a secondary lining, in which the radial joints and the interaction between the segmental lining and the surrounding soil will be simulated by a series of concentrated and distributed springs, respectively. In contrast to the radial rigid connection that was assumed in previous studies, radial detachment and tangential slippage between the segmental and secondary linings will be allowed. The solutions for the internal forces and deformations will be derived using the state-space method with arbitrary loads and joint distributions. In addition, the proposed method will be extended to cases with partial reinforcement that have a segment of secondary lining and a reinforcement connected by bolts. The proposed method will be validated using finite element numerical simulations. In addition, the variations in the internal forces and deformation for the soil reaction stiffness under different joint and interfacial stiffnesses will be examined. The results indicate that the internal forces and deformations of the linings decreased with the increase of soil reaction spring stiffness, and the interfacial radial spring stiffness had a more significant influence on the axial force transfer between the linings.

The shear strength model, a predictive method for effectively characterizing the shear strength of joints, can be used to evaluate the stability of the rock mass. However, the traditional shear model is difficult to apply due to its complicated form. Considering the complicated mapping relationship between joint shear strength and influencing factors, this study combined the back-propagation (BP) neural network to propose a new model for predicting the shear strength of rock joints, which can comprehensively consider various influence factors, including external shear test conditions and surface morphology of joint itself. Direct shear tests of granite joints were carried out to verify the proposed model, and the results showed that the outputted peak strengths training by the BP neural network match well with the measured values. At last, a comparison of the proposed model with Grasselli’s model and Xia’s model showed that the overall prediction error based on the proposed model is smaller and more accurate. It is seen that the BP neural network prediction model has a reliable estimate of the peak shear strength for rock joints.

The probability density function or cumulative distribution function of shear strength parameters is commonly unknown, and the first-order reliability method, second-order reliability method, and Monte Carlo simulation cannot be applied. Considering this challenge, a method to calculate the failure probabilities of two- and three-dimensional seismic slopes based on the fourth-moment normal transformation (FMNT) is proposed in this study. Moreover, there is a well-known negative correlation among shear strength parameters, which is commonly neglected in reliability analyses. Generally, only the marginal distributions and correlation coefficients of variables are known. In this case, the FMNT is no longer applicable. Therefore, a copula-based sampling method (CBSM) was proposed to construct the negative correlation among the shear strength parameters in this study. The effects of different probability distributions of shear strength parameters on the failure probabilities were investigated by CBSM and FMNT for seismic slope stability in this study. Two study cases were addressed to investigate the difference in reliability analysis of seismic slopes between CBSM and FMNT.

A multiscale simulation method for modeling granular materials was proposed in this paper. The key links in this method were analyzed, and the computing framework was constructed. In this multiscale approach, the finite-element method was used to simulate the boundary value problem. From the discrete particle aggregation embedded in each gauss integral point, the constitutive relation was extracted for the overall solution. This approach did not require complex constitutive hypotheses on the macroscopic scale. The description of the contact constitutive behavior between particles was relatively simple on the mesoscopic scale. Meanwhile, the macroscopic response could be effectively described by the mesoscopic mechanism. After a program verification, a representative test was numerically modeled using this technique. Through biaxial compression multiscale test of particles, macro–mesoscopic mechanical properties were investigated. The present approach may prove useful in expanding our understanding of the mechanical behavior of granular materials.

The air-boost vacuum preloading method has become popular in soft soil foundation reinforcement, especially in land reclamation projects. However, there are still some consolidation mechanism issues that need to be investigated, especially with respect to the determination of the air-boost pressure and duration. In this study, a set of macro- and microlaboratory tests including scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were carried out to investigate the improvement effects of different working pressures and durations. The test results indicated that air-boost vacuum preloading can enhance the consolidation efficiency, and the water discharge and surface settlement distinctly increased after gas injection. As a result, the tests with higher pressures and longer durations have higher strength and increment of the degree of consolidation (DOC). In some ranges, the higher pressure leads to the longer consolidation period, and the longer duration improves the effectiveness of each pressurization cycle. Based on the result analysis, the air-boost vacuum preloading process after pressurization could be divided into three stages, and the second stage was the most sensitive to changes in the air-boost pressure and duration. Furthermore, the increasing setting of air-boost pressure and duration was more suitable for the consolidation process in air-boost vacuum preloading.

Reinforcement geometry has a major effect on design parameters and stability control of reinforced soil structures. Geosynthetic with varying dimensions may be of interest from both economic and technical viewpoints. To understand this, pullout tests were conducted on four groups of geosynthetic reinforcements including geogrid with varying diameter of added transverse bars, geogrid with varying thickness, geocomposite with varying width, and ordinary geosynthetics. In these tests, poorly graded silica sand was used with 80% relative density. Results of the tests performed on the geosynthetic reinforcements with the same surface area and various geometries reveal that increasing the cross-sectional area in the front part of geosynthetics has greater influence than that of the rear part. This is due to the greater tensile force and displacement at the frontal part of the reinforcements than those at the rear part. Furthermore, by increasing the frontal cross-sectional area of the reinforcements, dilative behavior of the samples was also increased during the pullout tests. It was also observed that in the geocomposite with increasing width, tensile force distribution and displacement at the middle part having head width are greater than those at the sides indicating nonuniform distribution of tensile force in the transverse direction.

The permeability of a saturated porous medium is regarded as a constant during the seepage process in traditional seepage analysis theory. However, it changes constantly during the piping process. This study will consider the porosity dependent changes in the permeability of a saturated porous medium during piping. The critical hydraulic gradient of piping will be deduced and the relationship between the permeability coefficient and the porosity will be considered using Kozeny–Carman's formula during the piping process in this study. The transient seepage finite element program will be applied to simulate the initial seepage field, and then whether the piping occurs in the elements will be judged. The relationship between the seepage flow and the sediment content will be used to calculate the sediment loss quantity in the piping element, and the change of the porosity in the piping element will be further calculated. Moreover, the permeability coefficient of the piping element will be adjusted according to the formula between the permeability coefficient and the porosity. With the repetition of the aforementioned process, the piping process will finally be achieved. By comparing the numerical example with the experimental result, the validity of the proposed method will be verified.

Suction caissons with internal bevels at the caisson tip can effectively reduce resistance to make them to penetrate into the seabed easily. This paper describes the failure mechanisms of the soil at the caisson tip with internal bevels during suction-assisted penetration. The theoretical solutions to the bearing capacity factors N_c and N_γ are deduced in terms of the caisson tip geometry ratio of the flat section of the caisson tip to the caisson wall thickness (m/t), the inclination angle (δ) of the internal bevel from the horizontal, adhesion factors (α_i) along the inside and (α_b) at the base of the caisson tip. The influences of the caisson tip geometry ratio, the inclination angle, and the adhesion factor on the bearing capacity factor N_c are investigated under two limit conditions with smooth and rough bases of caisson tip. Theoretical results indicate that the factor N_c increases with increasing caisson tip geometry ratio, adhesion factor, and decreasing inclination angle. In particular, factors N_c of the caisson tip with rough base are greater by 0.57 than those with a smooth base. Furthermore, factors N_c of the flat caisson tip (m = t) are greater by 2δ than those with full internal bevel (m = 0). Finally, the required suction to install the caissons was obtained through the force equilibrium in the vertical direction. The numerical simulation and experimental results are used to verify the rationality of the presented failure mechanisms and theoretical results.

When constructing subway tunnels, blasting is commonly used to deal with granite boulders in weathered granite formations. It is, therefore, crucial to evaluate how the blasting-induced impact loading affects surrounding granite residual soil. By means of laboratory impact tests at different conditions, this paper presents the mechanical responses of granite residual soil. High-speed impact loading affects the soil in two ways, namely, (1) increasing the shear resistance; and (2) damaging the soil structure. Cyclic impact tests reveal the critical peak stress A_cr, which approaches soil apparent preconsolidation pressure. When the peak stress exceeds A_cr, the soil is severely damaged and the accumulative deformation increases sharply, indicating that the cementation of soil is destroyed. Besides, the soil is most resistant to impact loading at a threshold value of the loading frequency f_th and exhibits better resistance under high confining pressures. A framework was proposed that reflects soil structural damage and within which the failure mechanism under impact loading is explained. The damage to the soil structure generated with energy dissipation is the decisive factor in soil failure, and the accumulation of permanent deformation is the direct reason why soil fails. Three response modes were proposed for studied soil under impact loading. This research provides parameters for subway tunnel construction and enhances the understanding of granite residual soil under impact loading.

This paper presents a generalized yet simple mapping rule for image point identification in 3D bounding surface plasticity (BSP) models. It is based on the determination of the correct locations of the current and reversal stress points in the principal stress space using the eigenvectors of the stress tensors. To this end, a numerical procedure based on eigenvalue analysis is proposed to track the movement of the stress points in the principal stress space. To highlight the salient features of the approach, the mapping rule is implemented in a 3D BSP model. Numerical results and comparisons with laboratory data are provided, demonstrating the capability of the model to capture the soil response under triaxial and multiaxial loading conditions.

The double reduction method (DRM) is used to evaluate slope stability by weakening the two strength parameters in the Mohr–Coulomb criteria with two different reduction coefficients. The literature suggests various optimal reduction coefficient combinations (RCCs), but there is a lack of a suitable index to evaluate these combinations. The dissipated energy corresponds to the degree of material damage and the release of anti-sliding force of a slope. The higher the released anti-sliding force, the more serious the damage of the slope and the greater the associated dissipation of energy. Homogeneous slope examples show that different RCCs result in different dissipated energies when a slope becomes unstable. The dissipated energy can be used as an evaluation index to find the relative optimal RCC, which releases the greatest anti-sliding force of a slope from alternative RCCs. At the present stage, this method is limited only to homogeneous slope with two reduction coefficients.

Rocks in geothermal reservoirs are often subjected to cyclic thermal shock, the stable operation of the enhanced geothermal system (EGS) is affected by the physical and mechanical properties of rock. There is no sufficient basis for the selection of thermal shock parameters in previous experiments. To this end, this study selected temperature level, constant temperature duration, and thermal shock number as the experimental variables and conducted thermal shock treatment on coarse marble specimens. Then, scanning electron microscope (SEM) tests were used to provide variations in microscopic structure, uniaxial compression tests were carried out, and acoustic emission (AE) technology was applied to investigate the mechanical behaviors and fracture features. The increase of temperature level and the thermal shock number have different degrees of adverse effects on the physical and mechanical properties of rock specimens. The cracks between crystals become larger with the increase of thermal shock number and the crystal structure is gradually destroyed with the elevation of temperature. Two hours is considered as the threshold of constant temperature duration, after which the physical and mechanical properties of specimens stabilize. The temperature level has the greatest influence on crack-initiation stress and crack-damage stress.

A loading test device with infiltration function is developed to conduct model tests on the bearing behavior of single piles in expansive soil. The infiltration observation test and vertical static-load test before and after infiltration are carried out. Meanwhile, a two-phase nonlinear analysis approach is put forward to research the bearing characteristics of single piles in expansive soil by considering the influence of water infiltration. The method is divided into two phases: the infiltration phase and post-infiltration loading phase. In the infiltration stage, based on a load transfer function that can simultaneously describe the distribution of positive and negative frictional resistance, combining with the variation law of soil heave with depth, a nonlinear analysis method to calculate internal forces of single piles during water infiltration is proposed. Based on the infiltration stage, the formulas for calculating the bearing capacity of single piles in expansive soil after water infiltration are derived by taking into account the residual displacement of the pile–soil interface caused by soil heave, in the post-infiltration loading stage. The validity of the proposed approaches are confirmed through comparisons with the tests results. It is found that in medium-expansive soil, the relative displacements of pile top and surface increase rapidly with time, and then tend to be stable after about 14 days. Positive and negative frictional resistances occur along the pile shaft during water infiltration. Axial forces are tensile along the pile shaft, and the neutral point is found at one-half of the pile length. The bearing force of single piles in expansive soil after water infiltration is reduced obviously than that before water infiltration.