International Journal of Geomechanics

A three-dimensional microscale framework utilizing the discrete-element method is utilized herein to analyze the seismic response of a soil-retaining wall system in the time domain. The granular soil deposit is idealized as a set of spherical particles while the retaining wall is modeled as a rigid body composed of glued particles to yield the physical characteristics of a real-life gravity-type retaining structure. The model inherently accounts for the influence of material nonlinearity, potential phase shift between the wall and soil deposit, and viable failure of the wall by overturning or slippage. The effect of the amplitude and frequency of the input dynamic excitation on the response of the system is studied. A comparison is made between simulation results and those of the popular pseudostatic Mononobe–Okabe (M–O) method. This comparison showed that, in general, the M–O method is conservative. However, soil thrust and deformation of the structure showed dependence on the frequency of the input motion at the same amplitude and peaking at frequencies of input motion close to the natural frequency of the deposit. The simulations also showed that soil pressure distribution on the sides of the wall changed with movement and displacement of the wall. Maximum soil thrust occurs when the wall moves toward the backfill, and minimum soil thrust when the wall moves away from the backfill. Additionally, residual earth pressure may increase after shaking. Finally, the phase difference between local maxima time instances in wall acceleration and corresponding local minima in total dynamic soil thrust was also observed.

The longitudinally inclined (the tunnel excavation direction) ground surface often appearing at the shallow tunnel entrance and exit zone threatens and reduces the tunnel face stability. However, studies on this stability have rarely accounted for this inclined angle. Therefore, the effect of this inclined angle on the shallow tunnel face stability is considered, and the corresponding three-dimensional (3D) failure mode is constructed in this article. Then, the expression of active failure pressure is obtained using a nonlinear Mohr–Coulomb failure criterion based on the principle of virtual work. The upper-bound solution of it is examined based on the sequential quadratic programming method. The active failure pressure and failure mechanism are presented based on a series of studies of the key parameters. The results demonstrate that the shallow tunnel face stability is more dependent on the inclined angle (δ), tunneling length (L), and nonlinear shear strength parameters. Under nonlinear conditions, the influence is more significant. When the ground surface failure region is zero, the dimensionless parameter (C/D), tunneling length, and ground surcharge (σ_s) have no effect on the result. In addition, the longitudinally inclined ground surface is easy to induce the active failure of the shallow tunnel face.

Rocks with a layered structure (bedding or foliation) usually exhibit different levels of anisotropy in terms of deformation, strength, and failure mode under multiaxial stress conditions. This anisotropy is influenced by the spatial relationship between the internal layered structure and the principal stresses; however, relatively few experimental studies have been conducted due to various limitations, resulting in insufficient knowledge of the failure mechanism of layered rocks. A series of true triaxial compression tests for a gneiss were carried out considering the orientation of schistosity. The results show that the orientation of schistosity has a significant impact on the strength and failure of this gneiss. More specifically, under the same intermediate principal stress σ₂, the strength of specimens increases as the angle (ω) between the strike of schistosity and the direction of σ₂ increases. The greater the angle ω, the more sensitive the strength varies with σ₂. When σ₂ is low, the schistosity plane acts as a weak plane to control the failure of the specimen, and the main failure plane is parallel to the schistosity. As σ₂ increases, the weakening effect of schistosity decreases, and the influence of σ₂ on the failure is enhanced. In this case, the failure of cutting through the rock matrix more commonly occurs, and the failure plane dips toward σ₃ and strikes parallel to σ₂.

Based on an actual engineering case, this study focused on the limit support pressure, instability mechanism, and instability failure mode of the excavation face in the sand pebble stratum when crossing below the Yellow River. First, PFC3D was used to investigate the instability mechanism and failure mode of the excavation face in the sand pebble stratum. Then, the Terzaghi loose earth pressure formula was reasonably modified, and the limit support pressure was derived using this modified formula and the limit equilibrium mechanics model. Finally, the result was compared with those of an indoor test and a numerical simulation. The research showed that the calculation method proposed in this study was more suitable for underwater shield tunnels and formations where the soil arching effect is evident. The support pressure had a significant influence on the instability failure mode, whereas the influence of the buried depth was small. The limit support pressure decreased with an increase in the internal friction angle, a decrease in the water cover depth, or a decrease in the angle between the maximum principal stress direction and the horizontal direction.

Rammed earth (RE) is a low-embodied-energy construction technique that attracted the attention of engineers in recent years. To date, few studies have investigated the chemical deterioration of RE. This study investigated the durability of cement-stabilized rammed earth (CSRE) for 1 year under aggressive environments. Three cement contents were considered for preparing the CSRE specimens. They were exposed to acidic, alkaline, sulfate, and high-moisture environments. The mechanical properties of the CSRE specimens were determined at intervals of 1, 3, 6, 9, and 12 months of immersion in solutions. Results revealed that the sulfate environment was the most destructive solution for the CSRE specimens, which caused complete degradation of low-cement specimens and significantly decreased the compressive strength of high cement content CSRE. Scanning electron microscopy demonstrated the formation of ettringite for specimens submerged in sulfate solution. CSRE with small cement content was also completely disintegrated after 6 and 9 months of exposure in alkaline and acid environments, respectively. However, the acidic environment did not considerably affect the compressive strength of higher cement content CSRE, and the alkaline environment improved the compressive strength. Mathematical relationships are proposed between the compressive strength, Young's modulus, and ultrasonic pulse velocity for higher cement content specimens. Finally, multiobjective optimization by desirability function was used to minimize the cement content and maximize the compressive strength, simultaneously.

This paper investigates the bearing capacity of strip foundations resting on a cohesive-frictional soil sloping ground under both static and seismic conditions by applying the kinematic theorem of limit analysis. With the consideration of a composite collapse mechanism involving a generalized continually deforming shear zone, analytical expressions are established by incorporating the coupled influence of the soil resistance contributed by the cohesion, angle of internal friction, and self-weight of the soil mass. The loading conditions owing to inertia forces of supporting structures and the changes in the body forces of the supporting soil medium occurred during an earthquake are included in the analysis based on a pseudostatic approach. Rigorous upper-bound solutions are presented in the nondimensional form as charts and tables for the practical range of parameters that are normally encountered in the field. Additionally, by extending the concept of slope stability, a closed-form expression is proposed for computing the limiting values of horizontal seismic acceleration coefficients beyond which the sloping ground becomes unstable. The importance of the consideration of coupling effects of the soil resistance toward evaluating the static and seismic bearing capacity of foundations on the sloping ground over conventional approaches is discussed.

The failure mechanisms of unreinforced and reinforced layered rocks with various layer dip angles were analyzed using acoustic emission (AE) activities, failure modes, and load–displacement responses. The results indicate that the failure mode for both unreinforced and reinforced specimens changes from splitting in the hard layer to shearing in the weak interlayer as the interlayer dip angle increases. The presence of a rock bolt can greatly influence the load–displacement responses and the evolution of AE activities of reinforced layered rocks when the interlayer dip angle ranges from 45° to 60°. Only in this angle range can the rock bolts delay or prevent the formation of splitting cracks. There is a critical interlayer dip angle (60° in this study) at which both strengths for the unreinforced and reinforced specimens can achieve their lowest values. At this critical angle, the most significant reinforcement effect can be obtained. Further analysis indicates that at this critical angle the reinforcement effect decreases as the interlayer thickness and interlayer strength increase.

The curing stress is an important parameter affecting the mechanical properties of the cement-treated soil. This paper presents the effects of curing stress on the compressive and physical properties of the cement-treated dredged sediment (CDS). The plasticity behavior of CDS is affected by both the cement content and curing stress, whereas the particle size of CDS is mainly influenced by the cement content. The curing stress can reduce the compressibility of CDS significantly and slightly change the compression behavior of the postyielding stage, which is related to the structural behavior of CDS in the compression process. Finally, the strength factor related to the curing stress and cement content was proposed to predict the strength of CDS.

In this study, the accumulated plastic strain (APS) of granite residual soil under cyclic loads is investigated by a series of undrained cyclic triaxial tests. Granite residual soil is a special kind of soil that is widely distributed in areas of rapid economic development. Owing to a lack of understanding of the cyclic deformation of granite residual soil, the effects of several essential stress conditions, such as cyclic shear amplitude, initial static deviatoric stress, and effective consolidation stress, are explored and analyzed on the APS growth with loading cycles. The cyclic loads represent the typical traffic load acting on the foundations of subgrade works. Based on the results of tests under various stress conditions, a simple and easily adopted accumulated plastic strain growth (APSG) model is correlated to predict the evolution of APS with loading cycle number. Through comparing the results of separate tests, the APSG model is validated and exhibits its ability to predict the accumulated plastic behavior with satisfactory accuracy. Furthermore, the APS growth with a loading cycle is examined under various stress conditions by the APSG model. The influences of those important stress factors on the APS behavior can be successfully described by two often-used parameters in soil dynamics, that is, cyclic stress ratio and static deviatoric stress ratio, which are involved in the APSG model. As a result, the characteristics of plastic deformation of granite residual soil under cyclic loading conditions can be further analyzed by the new model. Although this model is easy to adopt with some accuracy, a more powerful model based on rigorous theory is still needs to be developed in the future. The finding of this study will provide a deeper insight into the cyclic loading behavior of granite residual soils that are often encountered in the subgrade of traffic engineering in China.

Root reinforcement is an interesting and environmentally favorable measure for soil stabilization. When properly applied, it can improve soil strength significantly. The paper presents a simulation of a series of drained triaxial tests on soil samples with different levels of root reinforcement in a form of three 5-mm-thick layers, located on different heights. Modified Cam-clay extended for unsaturated soils containing plant roots is used in calculations. The tests are modeled numerically and the results are compared with experimental results from the literature. Missing soil and root parameters are obtained based on the model calibration and further applied in the calculations of the stability of the vegetated slope subjected to rainfall. The influence of the initial root mass in the reinforcing superficial soil layer on the time after which a landslide occurs is investigated. The results suggest that even a minor level of root reinforcement may postpone the development of a rainfall-induced landslide.

The theory and model tests for active earth pressure on a cantilever pile wall adjacent to existing basement exterior wall are studied in this paper, taking noncohesive sand as the research object. The ultimate rupture angle is presented with the global static equilibrium method based on the movement mode of a flexible retaining wall rotating about the base and the plane sliding surface. The soil arching theory is introduced to obtain the coefficient of active earth pressure in the subarea, in which the trajectory of minor principal stress after stress deflection is assumed to be a circular arc. Taking account of the effects of shear stress between differential level layers and the nonlimit state of the lower soil layer, the differential level layer analysis method is modified and the solution for the unit earth pressure, the resultant force, and the height of action point of the resultant force are derived. The model tests are conducted to simulate the deformation and the progressive failure process of the sand with limited width under the movement mode of the flexible retaining wall rotating about its base. Analysis and processing of the images observed from the model tests was compared with the rupture angle calculated with the proposed method and showed that the method can provide a good prediction. The lateral earth pressure decreases with the decrease of the ratio of width to height in the critical width range. Considering the effects of the nonlimit state and the partial mobilization of the shearing resistance of the lower soil layer, the internal friction angle has been reduced based on shear strength reduction theory, consequently the calculated lateral earth pressure agrees with the measured result from model tests. The upper part of the theoretical distribution curve is close to a linear line and the lower part is a concave upward nonlinear curve while its distribution law is the same as the measured curve. The action point of the resultant force under the movement mode of rotation about the base is located at the height of 0.27–0.31 wall within infinite width sand filling.

The natural structure of columnar jointed rock mass (CJRM) is complex because it was formed during the cooling process of volcanic rock. In CJRM, both the structures of columns and columnar joints are oriented, and the exact mechanical properties are difficult to obtain due to the lack of testing samples that correspond to natural rock masses. Therefore, this brings challenges for underground engineering construction related to CJRM. The reconstruction of CJRM is an effective method that can be used to resolve this problem. However, using an artificial method means that it is difficult to consider the detail of structures, such as irregular columns, columnar joints, and microcracks in columns. With the development of 3D printing (3DP) technology, a useful method for the accurate reconstruction of CJRM has been provided. In this paper, based on laboratory and in situ tests, the structural characteristics and mechanical properties of CJRM in Baihetan Hydropower Station will be investigated. Then, based on the accurate structural reconstruction of CJRM that considers the similarity constant between in situ and laboratory tests, the mechanical anisotropy and failure modes of 3DP CJRM specimens will be investigated. The results show that 3DP is an effective method for reconstructing the structures of CJRM and that it is necessary to consider the detail of the structures, such as the irregularity of columns, columnar joints, and microcracks. In addition, the unfavorable loading angles between the axis of the column and loading direction were obtained. The 3DP results presented in this paper could provide a reference to help understand the structural characteristics of CJRM.

Particle image velocimetry (PIV) is a hybrid experimental–digital technique that allows for the noncontact measurement of the displacements and strains in granular media. It has seen widespread applications in the laboratory studies of geostatic problems, such as slope failures and ground deformation due to foundation punch-through. In recent years, the development of optical cameras with high temporal and spatial resolution opens the possibility of extending the PIV technique to dynamic problems such as those caused by impact. Using PIV for impact measurements requires the images to be taken at very high frame rates. In this paper, an attempt is made to capture the phenomenon of low-velocity impact wave propagation in sand using PIV. Details of the experimental setup are presented, and the key factors that affect the accuracy of the measurements are discussed. The PIV results are processed to obtain the displacement, velocity, and acceleration histories for particle patches at varying distances from the impact source. Comparisons are made against independent concurrent measurements recorded by two accelerometers embedded in the same soil sample, as well as the results from a dynamic finite-element analysis that computes the displacements and stresses in the sand due to the same impact loading. This study indicates that, for dynamic measurements in low-velocity impact experiments, the PIV technique offers a promising nonintrusive method of capturing the displacement, velocity, and acceleration histories over a wide range of locations in the sand mass without needing to embed sensors in the test sample.

This paper presents an experimental study on the pullout behavior of a vertical plate anchor buried in sand under lateral loading, using the digital image correlation (DIC) technique. Based on image analysis, the influences of anchor embedment ratio, sand relative density, and sand–plate interface friction on the failure and deformation mechanisms were discussed. With lateral displacements, the plate anchor experienced passive soil pressure in the front and active soil pressure from the behind. It is observed that the passive failure surfaces varied from approximately linear to be curved and finally became locally rotational with increasing embedment ratios, which indicated that the failure mode transitioned from general shear to be local shear gradually. The failure process is progressive in nature, and the critical embedment ratio is sand-state dependent. With an increasing relative density of sand, the front passive failure zone became larger, whereas the scope of the active failure zone reduced. A wider range of soil may be mobilized by plate anchors of a greater interface frictional strength, leading to enhanced anchor capacity, and this effect decreased with increasing anchor embedment ratios and vanished for deep anchors. The test findings can provide useful visualized data for the development and verification of relevant theoretical models.

Numerical analyses have been widely used to investigate the stability of deep excavations. The results of this type of analyses rely on the constitutive model that is adopted for the analyses. Although many advanced constitutive models have been developed for the simulation of soil behavior, they are often complex, expensive to use, and not well understood by practicing engineers. Hence, simple constitutive models, such as the Mohr–Coulomb model, are widely used in geotechnical engineering practice. However, these simple models, fail to represent some key features of soil behavior. Of particular importance in granular soils is the effect of changes in soil density on the soil behavior, an aspect that is often overlooked when simple constitutive models are used. In this study, a series of triaxial tests will be conducted on reconstructed gravelly sand to investigate the effect of the relative density and confining pressure on strength and stiffness characteristics of the soil. According to the test results, variations of the soil stiffness and peak deviatoric stress with relative density and confining pressure will be established. A novel disturbance function will then be proposed based on the disturbance state concept to capture the effect of soil density on its behavior. Subsequently, a constitutive model that is based on the original Duncan and Chang model will be developed that considers the effects of the confining pressure and relative density of the soil using the proposed disturbance function. The model is implemented in ABAQUS software and is verified by comparing the numerical results with experimental data. The application of the model is presented through the simulation of a deep supported excavation. The numerical results show that the model successfully simulates horizontal displacements of the support piles, with errors of <5% for the monitoring points. In particular, it is highlighted that the model is superior to the widely used Mohr–Coulomb model in the simulation of excavation problems, and yielded a safer design than that obtained using the Mohr–Coulomb model.

In practice, it is quite common for soils to be mixed and compacted at moisture contents lower than the optimum moisture content (OMC) or lime content less than the optimum lime content (OLC). This study investigates the effect of not achieving the target of OMC or OLC on the volumetric behavior (swelling and shrinkage) and swelling pressure under swell–shrink cycles. The selected expansive clay was a residual soil derived from weathered Quaternary age basaltic rocks in Western Victoria, Australia. A series of cycles of swell–shrink tests were conducted at different initial lime contents, moisture contents, and stress levels. Vertical deformation and swell–shrink cycles' relationship were obtained and analyzed. The results showed that all specimens tested reached the equilibrium condition after the third swell–shrink cycle. The outcome of investigating the effect of not achieving the target of OLC showed that the maximum swelling occurred on the second cycle changing the degree of expansion from being moderate to very high expansive clay. This result recommended a review of current pavement design procedures to consider the cyclic swell–shrink potential to simulate the field condition for the longer term. However, for investigating the effect of not achieving the target of OMC, the results showed that the maximum swelling occurred at the first cycle, and this suggests that the effect of swell–shrink cycles could be neglected for the long term. This study also showed that at constant moisture content, the swelling pressure decreased as compaction stress decreased; however, at the constant compaction stress, the swelling pressure decreased as moisture content decreased.

Overlooking the anisotropic behavior of soil with directional shear strength parameters can lead to unrealistic estimation of the actual limit load. This research is focused on the effect of the shear strength anisotropy on the bearing capacity of surface footings near slopes. The lower bound limit analysis in conjunction with the finite element method and linear programming technique was employed to estimate the limit pressure. The Mohr-Coulomb yield function and an associated flow rule were adopted, and the soil-foundation interface was assumed rough. The limit pressure of the foundation was expressed as a function of effective dimensionless parameters, including the cohesion and internal friction angle anisotropy degrees, slope angle, and the distance from the foundation to the slope. Finally, 3D applied charts were presented to estimate the effect of the anisotropy on the bearing capacity of surface footings near soil slopes.

Hydraulic conductivities of soils rely significantly on three factors, the properties of their pore water, the relative quantity of their pore water, and changes in their pore structure. For saturated soft soils, that demonstrate a considerable degree of alteration in pore structure during densification, it is important to consider their volume change behavior when evaluating their transitional hydromechanical properties during evaporation. This paper reports on the evaluation of hydraulic conductivity functions (HCF) of two saturated soft soils using the evaporation method. The HCF of the samples will be established using the measurement of water loss and the associated gradient during evaporation. By recognizing the importance of the volume change behavior of deformable soft soils on their transitional hydromechanical properties, a theoretical formulation is suggested to incorporate their volume change behavior when estimating their transient hydraulic conductivities. An increase in the hydraulic conductivities of approximately one order of magnitude has been observed when volume change in the samples have been quantitatively considered in their calculation compared with cases when this type of effect is not considered. HCFs established using this approach, taking into consideration the volume change behavior of the samples, will be compared with those obtained through one-dimensional consolidation tests. The proposed method has the potential to provide HCF measurements at high void ratio ranges, where 1D consolidation tests would not be effective due to the highly fluidized condition of the material. Based on experimental results and analysis, this paper establishes a generalized theoretical formulation to appraise the hydraulic conductivity functions of deformable soft soils using the evaporation method and takes into consideration the volume change behavior of the sample.

This study deals with the deduction of the stress intensity factor (SIF) for the propagation of rectilinear semi-infinite noncentrally located interfacial crack influenced by propagating SH-waves in the framework of two different dry sandy layers composed of a strip under various loading conditions. Two-sided Fourier integral transform, Liouville's, and Abel's theorem along with the Wiener–Hopf technique serve as a salient feature of the adopted mathematical treatment. The analysis has been carried out for constant loading (CL) and stress-free (SF) cases under nonharmonic loading (NHL), and for constant amplitude of vibration (CAV) and SF cases under harmonic loading (HL). Moreover, the expression of SIF for the static crack has been obtained under various conditions of NHL and HL as a limiting case. The effects of various existing parameters, viz., dry sandiness ratio, width ratio, sandiness parameter of upper and lower layers, inhomogeneity parameter on the SIF for the previously mentioned cases along with comparative analysis for differently configured dry sandy elastic strips have been investigated numerically as well as graphically.

When simulating large rotation, the false volume expansion and elastic distortion problems of the block occurs severely in the original discontinuous deformation analysis (DDA). In this study, a new displacement formula that the elastic-deformation terms calculated before rotation is introduced. The formula is then linearized and used to modify the correlation submatrices. After each calculation step, the coordinate transformation is adopted to update the initial stress and strain-velocity vector. In the proposed remedies, the deformation of the block produced by centrifugal and Coriolis forces is considered automatically, and each of the deformation parameters has clear physical meaning. We further use several numerical examples to verify that the proposed method can eliminate the elastic distortion and false volume expansion problems exhibited by the original DDA. Finally, a real landslide case was analyzed to illustrate that the modified DDA is effective and useful.

In this study, a novel analytical approach is proposed for the calculation of active earth pressure on rigid retaining walls considering the influence of intermediate principal stress and soil arching effects. According to the Mohr-Coulomb strength criterion, horizontal and vertical stresses as well as the angle between the maximum principal stress and the horizontal direction of backfill soil units were derived. Through calculations performed on a horizontal thin layer of backfill soil, average vertical stress and coefficient of active earth pressure were obtained. Finally, active earth pressure distribution, active earth force, and the height of application were calculated based on the static equilibrium equation. Furthermore, effects of internal friction angle, intermediate principal stress weight parameter, and wall–soil interface friction angle on coefficient of active earth pressure were investigated. The results indicate that a coefficient of active earth pressure is smaller than traditional calculation methods when the intermediate principal stress is considered without regard to soil arching effects. In addition, it is observed that the coefficient of active earth pressure decreases with the increase of the intermediate principal stress weight parameter, but increases with the increase of the wall–soil interface friction angle. In addition, when different values are given to weight parameters of intermediate principal stress, different backfill soil active earth pressure calculation models can be deduced. Moreover, this analytical model was verified and provided satisfactory results when compared with experimental results and previous studies, it also can predict the nonlinear earth pressure distribution under various modes of the soil yield criterion.

Acid/alkali contamination of expansive soils, which has been probed in recent years, gives rise to unexpected structural failure when exposed. However, a systematic research aiming at evaluating volumetric behavior of natural illitic clays when subjected to acid/alkali solution as pore fluid and its microlevel analysis is not well established. A series of oedometer tests and microanalytical experiments (X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy) have been carried out to investigate the effects of acid and alkali contamination on swelling and compressibility of natural expansive clays from Heilongjiang province in China and to identify the underlying controlling mechanisms. Distilled water, sulfuric acid of pH 3, and caustic soda of pH 13 were selected as three different pore fluids. The results show that compared to samples inundated with water, specimens exhibit greater swelling and lower compressibility after being exposed to acid solution, and lower swelling and greater compressibility after being subjected to alkali solution. In three different soaking solutions, all samples present an increasing tendency for swelling deformation with dry density from 1.4 to 1.8 g/cm³, while the highest compressibility occurs at dry density around 1.5 g/cm³. The microanalysis revealed that soils undergo reactions, including desiliconization and cation exchange, due to the acid and alkali erosion, which correspondingly leads to changes in soil mineralogy and texture. Acid and alkali contamination results in disintegration and loose structure, and acid exerts more destructive impacts than alkali do. The sulfuric acid promoted the dissolution of tetrahedral cations, while the caustic soda improved the dissolution of octahedral cations.

For clays with low permeability, some experimental results show that there may exist a threshold hydraulic gradient, below which the water in clays cannot flow. This threshold hydraulic gradient induces a moving boundary problem in the model of consolidation that is difficult to solve analytically. To date, only analytical linear elastic consolidation solutions have been developed when the threshold hydraulic gradient is considered. The linear elastic models are, however, unable to capture the rheological behaviors of clays. In this paper, analytical and numerical solutions are derived for rheological consolidation under a multistage loading when the threshold hydraulic gradient is considered. Finally, the influences of the threshold hydraulic gradient and rheological model on consolidation behavior are investigated.