International Journal of Geomechanics

Transparent granular soil was recently found to be greatly useful for observations of the internal deformation in geotechnical model tests. Therefore, it is necessary to investigate the stress–strain and stress–dilatancy behaviors of transparent granular soil and also to propose a constitutive model for this material. In this study, drained triaxial shearing tests were conducted to investigate the stress–strain and stress–dilatancy relations of transparent granular soil. It was found that this material showed a state-dependent stress–strain behavior similar to that of sands. A state-dependent constitutive model within the framework of the critical-state theory was proposed to describe the stress–strain and stress–dilatancy behaviors of this material. This model was found to well describe the stress–strain behaviors (e.g., strain softening and volumetric expansion) and the hook-shaped stress–dilatancy behaviors from the test data in both the Group A (for the calibration of material constants) and Group B (for the validation of model predictions) tests. In addition, this model was found to well capture the changes of the peak-state strength, peak-state dilatancy and peak-state strains with the state parameter.

Granular materials deposited under gravity usually exhibit inherent fabric anisotropy, which leads to profoundly varying strength under different loading directions in regard to the bedding plane that has been observed through experiments and numerical simulations. Classical isotropic strength criteria that are only stress dependent cannot describe such anisotropy in strength. This study introduces an anisotropic strength variable Λ that measures the distance between the bedding plane and the maximum shear stress ratio plane, thus incorporating both the stress tensor and the material orientation, and guarantees objectivity. The strength variable Λ is adopted to construct a general formulation that allows for the extension of many existing isotropic strength criteria to become anisotropic. The formulation requires only the following two parameters: k_f0, reflecting the minimum strength of the material, and a, reflecting the intensity of inherent anisotropy. The two parameters can be conveniently calibrated. The proposed strength criteria formulation is validated against both physical tests and discrete-element method (DEM) simulations on various granular materials, showing its capability in describing the anisotropic strength. The anisotropic strength criteria formulation is applied to analysis of passive earth pressure to showcase the significance that considerations for strength anisotropy could make to geotechnical design.

Current geomechanical applications imply nonisothermal processes of unsaturated geomaterials, in most cases following stress paths different from the classical triaxial compression often used in laboratory testing. Although the effects of temperature, suction, and stress-path direction (Lode’s angle) on the strength of geomaterials have been investigated independently, an integrated analysis combining the three effects has not yet been performed. In this paper, a thermoplastic constitutive model for unsaturated conditions that accounts for the effect of Lode’s angle on the strength of geomaterials is presented. The yield surface evolves—shrinking for increasing temperature and expanding for increasing suction—and has its maximum strength for triaxial compression and its minimum for triaxial extension. Examples that can be related to geoenergy applications highlight the importance of accounting for the effects of temperature, suction, and Lode’s angle on the evolution of the strength of geomaterials. Numerical results show that not considering these effects may give rise to misleading predictions of the strength of geomaterials.

Lengthy retaining walls are typically required in several geotechnical applications. Compacted soil is the classic backfill behind such walls, yet soil has a high unit weight that imposes large lateral loads and may lead to outsized wall dimensions. Geofoam or foam made of expanded polystyrene (EPS) can substitute the soil backfill due to its light weight and high compressibility and can reduce the lateral static loads imposed on walls. In this paper, EPS mechanical properties were measured in addition to the interface friction between this geomaterial and other materials, such as sand and concrete. A reliability analysis was conducted to develop the partial resistance factors required for the main EPS properties. Using a three-dimensional (3D) numerical analysis, the reliable EPS properties were used in the hardening soil constitutive model to simulate flexible walls with EPS inclusions of various thicknesses. Analysis outcomes were verified against measurements from a physical prototype and were also compared with results from the literature. From the main outcomes, the lateral pressure on flexible walls can be significantly reduced by up to 25% using a relatively thin EPS inclusion, and design charts for the reduction in the lateral pressure are provided.

Triaxial compression tests were carried out on artificially structured soil samples at confining pressures of 25, 37.5, 50, 100, 200, and 400 kPa. A binary-medium constitutive model for artificially structured soils is proposed based on the experimental results, the disturbed state concept (DSC), and homogenization theory. A new constitutive model for artificially structured soils was formulated by regarding the structured soils as a binary medium consisting of bonded blocks and weakened bands. The bonded blocks are idealized as bonded elements whose deformation properties are described by elastic materials, and the weakened bands are idealized as frictional elements whose deformation properties are described by the Lade-Duncan model. By introducing the structural parameters of breakage ratio and local strain coefficient, the nonuniform distribution of stress and strain within a representative volume element can be given based on the homogenization theory of heterogeneous materials. The methods for determination of the model parameters are given on the basis of experimental results. Comparisons of predictions with experimental data demonstrate that the new model provides satisfactory qualitative and quantitative modeling of many important features of artificially structured soils.

Geotechnical engineering is dominated mostly by uncertainties, because it always deals with highly variable natural materials. Reliability-analysis approaches emerge as a more reasonable and rigorous way of handling uncertainties. Two-dimensional stability assessment of rock slopes is performed, and the probability of failure of rock slopes against planar sliding is determined using the random fields. Both cohesion and friction coefficient along a discontinuity are treated as a normal random field and are represented by the mean values, standard deviations, spatial correlation lengths, correlation coefficient, and cross-correlation length, which account for the cross correlation between cohesion and coefficient of friction. Several examples are used to verify the proposed approach. The numerical results obtained from the proposed method are in good agreement with the numerical results obtained from Monte Carlo simulations. Moreover, the proposed method provides a new approach to study two-dimensional stability of rock slopes.

This paper proposes an analytical approach to evaluate the time-dependent bearing capacity of a driven pile in clayey soils by taking the pile installation and subsequent reconsolidation effects into consideration. The process of pile installation is modeled by undrained expansion of a spherical cavity at the pile tip and a cylindrical cavity around the pile shaft. The cavity expansion solution, which is based on a K₀-consolidated anisotropic modified Cam-clay model (K₀-AMCC), is used to capture the pile installation effects. After pile installation, the dissipation of the excess pore water and the increase of the effective stress in the surrounding soil are evaluated by the radial consolidation theory. Based on the effective stress, the strength of the remolded soil is quantified by the modified Cam-clay (MCC) model and the spatially mobilized plane (SMP) criterion. With the three-dimensional strength of the surrounding soil, the time-dependent bearing capacity of the driven pile is evaluated by the total stress (α) method. To verify the proposed analytical approach, three groups of centrifuge model tests were performed, and the proposed approach was applied to predict the time-dependent bearing capacity of the tested piles. It is shown that reasonable predictions can be made by the method proposed in this paper.

Considering the real irregular shapes of ballast particles and complete track skeleton, a two-dimensional discrete element model is built to investigate the dynamic behavior of high-speed railway (HSR) ballasted track. Taking the moving wheel loads obtained from railway vehicle-track coupled dynamics simulation as the excitation inputs, the dynamic behavior of ballast particles in terms of contact force, stress, and vibration response are simulated using the discrete element model. Numerical results show that the ballast particles within the depth of 200 mm under sleepers would be most likely to carry a higher stress level when a vehicle passes by. Vibration amplitudes of ballast particles increase with the increase of vehicle speed, and the acceleration amplitudes rise sharply when the vehicle speed is higher than 200 km/h. Spectrum analyses indicate that the dominant frequencies of particle displacement and velocity are lower than 100 Hz, whereas the acceleration responses contain not only low-frequency but also some medium-frequency components in the range of 150–300 Hz. Simulated results also demonstrate that the vibration amplitudes of ballast particles attenuate with the depth and the longitudinal distance from the sleeper center to the particle. This research work presents mechanical behavior of railway ballast and provides a potential way to reveal the deformation and degradation aspects of railway ballast from the mesoscopic to macroscopic level, while recognizing the limitations of the current discrete element model in quantifying particle breakage.

Assessment of rainfall-induced shallow slope failures is important for reducing damage to infrastructures as well as for the safety of people living close to hazardous areas. The rainfall intensity-duration thresholds for initiation of slope failure (ID thresholds) based on the historical slope failure data are commonly used to assess slope failure. However, in these slope-stability assessments, the critical influence factors triggering shallow slope failures are often disregarded. Three sets of parametric studies were performed through finite-element modeling to investigate the effects of saturated permeability of soil, slope angle, and antecedent rainfall on instability of a shallow slope. It was found that the hydrological mechanism involving the rainfall-induced shallow slope failure is either (1) the rising of water table mode or (2) the rainfall infiltration mode. The hydrological mode during the failure depends on the magnitude of rainfall intensity compared with the infiltration capacity at the soil saturation state. The rate of reduction of safety factor (FS) increases with an increasing intensity of rainfall, only in a range lower than the infiltration capacity at the soil saturated state. As such, the saturated permeability of the soil, which is equal to the infiltration capacity at the soil saturated state, plays an important role in the shallow slope failure. The saturated permeability was also found to govern a range of applicability of the ID thresholds. If the rainfall intensity is not greater than the infiltration capacity at the soil saturated state, the rainfall duration to failure ($T_{rf}$) can be read from the ID thresholds. Slope angle and antecedent rainfall were found to play significant roles in the instability of shallow slopes, because they control the initial stability of slope, which results in the different linear relationship of ID thresholds. In addition, the slope angle might accelerate the rate of rainwater infiltration; hence, it reflects the slope of the ID thresholds.

This study focuses on the use of a thermomechanical soil-structure interaction (load transfer) analysis to assess the axial strains, stresses, and displacements during thermomechanical loading of energy piles in various soil deposits with different end restraint boundary conditions. After providing details of the model and its novel features, this paper presents a parametric evaluation performed to understand the roles of the soil shear strength parameters, toe stiffness, head stiffness, side shear stress-displacement curve, and radial expansion, as well as the magnitude of temperature change. This evaluation showed that the end restraint boundary conditions play the most important role in controlling the magnitude and location of the maximum thermal axial stress. The soil type also causes changes in the nonlinearity of the axial stress distribution throughout the energy pile. The radial expansion did not affect the thermomechanical soil-structure interaction for the conditions investigated in this study. The thermomechanical load transfer analysis was then calibrated to identify the parameters that match the observed soil-structure interaction responses from four case studies of energy piles in nonplastic soil or rock layers during monotonic heating, including one field study and three centrifuge studies. The ranges of calibrated parameters provide insight into the behavior of energy piles in nonplastic soils and can be used for preliminary design guidance.

The response of infinite cylinder expanding in a poroelastic medium is investigated analytically in this paper on the basis of Biot's consolidation theory. The approach is based on the local equivalence between the response of a perfectly plastic behavior to the monotonic loading process and an appropriate fictitious nonlinear poroelastic behavior. A simplified framework was adopted for the diffusion equation to derive a closed-form expression for pore-fluid pressure distribution, whereas stresses and displacements were computed numerically. The related theoretical results are discretized and critically compared to finite-element solution, showing good agreement in terms of radial stresses and normalized pore pressure distributions. For in situ testing, interpretation, and foundation design purposes, results interpreted in the space of normalized velocity (V) versus degree of drainage (U) demonstrate the model capability of capturing the transitions from drainage to partially drained and undrained soil regimes.

Drill bits, such as roller cones and hammers, are equipped with inserts; once in contact with the rock, each of them applies mainly a compressive action called indentation. In this paper, a numerical modeling-based analysis of single and double rock-indentation processes using the finite-element method is presented. Based on damage mechanics, Mazars’ model, initially developed for concrete, has been used to simulate the extent of the damaged zone within a rock in the vicinity of a spherical drill insert during single- and double-indentation processes. The effects of loading and insert spacing on the damaged-zone extent and the interaction between two neighboring inserts were investigated numerically and compared with the results of a recent experimental study. The latter used an image analysis–based technique applied on thick sections prepared from three types of rocks (granite, limestone, and sandstone) subjected to indentation tests. This procedure enabled quantification of the extent of the damaged zone within the rock samples under different indentation test conditions. Results of the proposed numerical analysis reveal that Mazars’ damage model is relevant to simulating rock response under indentation loading and that indentation-induced rock damage is caused mainly by extension strain development.

Based on the theory of elasticity, the analytical solutions of the Love-wave dispersion equation are generated for the inhomogeneous orthotropic medium, for which the Young’s modulus (E_x, E_y, E_z), shear modulus (G_xy, G_yz, G_xz), and medium density (ρ) are obeying the exponential law model (E_xe^αz, E_ye^αz, E_ze^αz, G_xye^αz, G_yze^αz, G_xze^αz, and ρe^αz) and the generalized power model [E_x(a + bz)^m, E_y(a + bz)^m, E_z(a + bz)^m, G_xy(a + bz)^m, G_yz(a + bz)^m, G_xz(a + bz)^m, and ρ(a + bz)^m]; however, three Poisson’s ratios (υ_xy, υ_yz, υ_xz) are constants regardless of depth. In other words, the aforementioned moduli and density of the upper orthotropic layer [with thickness (H)] and lower orthotropic half-space are assumed to vary exponentially and generalized power laws as depth increased. To explore the influence of the inhomogeneous characteristics of the orthotropic materials on Love-wave velocity, a parametric study was conducted by utilizing the granite’s parameters. The results reveal that the Love-wave velocity is markedly influenced by the inhomogeneity parameters (α, a, b, and m) but is unaffected by the presented isotropic/orthotropic rock types. Hence, it is imperative to consider the effect of inhomogeneities when investigating the behaviors of Love-wave propagation in the orthotropic medium.

Underhand cut-and-fill stoping is an efficient, sustainable mining method that is particularly applicable to complicated mining conditions in which both the peripheral rocks and the orebody are extremely unstable. Considering the mining conditions of the shallow, steeply dipping, narrow orebody in the Canzhuang gold mine in Shandong Province, China, a new method of underhand cut-and-fill without sublevel stoping that does not use the conventional sublevel, access to stope, and decline is proposed. Additionally, a novel auxiliary ventilation mode is applied to achieve high-efficiency ventilation. The restrained-beam mechanical model is established for the overlying backfill in single drift to ensure stability of the test stope. The plane problem is transformed into a three-dimensional problem when deducing the theoretical evenly distributed load of the overlying backfill. The optimal bearing layer thickness of the overlying backfill is calculated. During a 2-year field industrial test, the ore dilution ratio reduced from 14 to 4% and the ore recovery ratio increased from 75 to 92%, which improved the economic efficiency significantly and satisfied safe-production requirements. The description of the new mining method might provide theoretical and practical guidance for mining in similar settings.

The main objective of this paper is to establish a complete analytical solution concerning the linear pressure distribution under rigid rectangular spread footings. An eccentricity diagram is developed to map the unique footing deformations and compression zones in each one of five distinct regions. For each region, the linear soil pressure, neutral axis position, and pressure values at the four corners are expressed in closed forms. The accuracy and consistency of the explicit expressions are verified by presenting several special boundary cases, whereas the physical interpretation is brought out by analyzing the eccentricity diagram. A generic nomogram providing the maximum soil pressure is also formed to promote efficient structural footing design. The developed analytical formulas for responses and resultants enable algorithmic implications without iterations and offer high computational efficiency. Proper examples, generated via developed computer software, exhibit how the theoretical content of this article is applied in practice. The software enables three-dimensional (3D) viewing of the deformed and undeformed physical and mathematical model of the structure, allowing detailed visual inspection of the results.

When modeling the development of slip surfaces in strain-softening soils, the FEM can suffer from mesh dependency and a lack of convergence of the analysis. The calculation of strains using a nonlocal method avoids the independent softening of a solitary point that can cause these symptoms. Nonlocal methods calculate the strain at a point with reference to the strains at calculation points surrounding it. In this study, a biaxial compression analysis is used to compare the original and two modified nonlocal methods with local strain-softening analysis. Three nonlocal parameters are introduced, and their influence on the nonlocal strain calculation is investigated. Meshes with different discretizations permit a comparison of the mesh dependency of these methods and a sensitivity analysis of nonlocal parameters. All the nonlocal methods are found to have significantly less mesh dependency than the local method. Both modified nonlocal methods exhibit less mesh dependency than the original approach, but one of the two modified methods, the overnonlocal method, is shown to be unstable because the mesh is refined for certain values of the nonlocal parameters.

Pile foundations are usually used to transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock strata with a higher bearing capacity and stiffness. The type and size of a pile foundation that supports midrise buildings in high-risk seismic zones can alter the dynamic characteristics of the soil–pile–foundation system during an earthquake due to soil–structure interaction. To investigate these phenomena, a 15-story moment-resisting frame sitting on differently sized end-bearing and floating pile foundations was simulated numerically. The present paper describes a numerical modeling technique for the simulation of complex seismic soil–pile–structure interaction phenomena. By adopting a method of direct calculation, the numerical model can perform a fully nonlinear time history dynamic analysis to realistically simulate the dynamic behavior of soil, pile foundations, and structure under seismic excitations. This three-dimensional (3D) numerical model accounts for the nonlinear behavior of the soil medium, the piles, and the structural elements. Results show that the type and size of the pile elements influence the dynamic characteristics and seismic response of the building due to interaction between the soil, pile foundations, and the structure. The findings of this study can help engineers select the correct size and type of pile foundation while considering the seismic performance of buildings sitting on soft soil and aim at optimizing their design.

The compression behavior of structured soils after virgin yielding is highly nonlinear and cannot be captured by a single line in the e–ln(p′) space. The slope of the compression curve of structured soils changes gradually as the structure of the soil crashes and reaches to the slope of the same soil in the remolded state. When the initial and final values are known, the disturbed state concept can be used to describe the compression behavior of structured soils. In this study, the state of the structured soil at the beginning of virgin yielding was considered as initially intact, and its state after full destruction was considered as fully adjusted. The compression index of the soil at any particular state between these two states was described using a state function based on the experimental results. A compression model with a variable slope of the compression curve was developed using the distributed state concept. The proposed model was implemented in the modified Cam-clay model and verified using data available in the literature for oedometer and triaxial tests on structured soils. Comparison with the experimental results of triaxial shearing tests showed that the proposed model was able to describe the behavior of specimens with low overconsolidation ratios more accurately.

The accurate assessment of the stability of natural slopes and earth structures during earthquakes is a critical design aspect for seismically active areas. The Newmark-type displacement method, which is capable of estimating permanent earthquake-induced displacements, is extensively adopted to evaluate slope stability under seismic loading. However, this approach becomes unmanageable for regional assessment because hundreds or thousands of iterations are required to obtain the yield acceleration ($k_y$), which is estimated by trial and error in conventional slope-stability analyses. To reduce computational effort, a simple procedure is developed for the noniterative evaluation of $k_y$ for both shallow and deep slope failures. The factor of safety (FS) of slopes under static conditions is first calculated based on developed stability charts. Thereafter, $k_y$ is determined through its established correlation with FS. The $k_y$ calculated using the proposed procedure corresponds well with that obtained using the trial-and-error approach (5% difference). Thus, the proposed procedure can be applied efficiently in a regional assessment with thousands of slopes.

Many researchers have indicated how cementation allows treated soft clays to sustain a higher yield mean effective stress at the same void ratio as its reconstituted state, and thus, the strength of clay treated with cement increases because the cement and clay particles bond together. However, the void ratio of cement-treated clay decreases significantly in isotropic consolidation and triaxial conditions when subjected to a high mean effective stress, particularly beyond the initial yield stress. Laboratory experiments have shown that the cementation of clay gradually diminishes as the mean effective stress increases as a result of the degradation of cementation bonds. Thus, the failure envelope of cement-treated clay gradually merges with the reconstituted clay–cement mixture at high mean effective stresses. Furthermore, the shear strength of cement-treated clay is influenced by the shear degradation induced by shear deformation. In this study, by combining the mean effective stress and shear degradation, a constitutive model, referred to as the C3 model, based on the critical state framework, was developed to simulate the behavior of cement-treated clay. The proposed model includes a modified mean effective stress, a nonlinear failure envelope, a nonassociated plastic potential function, and a general stress-strain relationship to simulate the prepeak and postpeak deviatoric stress states, including the softening behavior of cement-treated clay. In this study, triaxial tests (drained and undrained) were conducted on Ballina clay treated with 10 and 12% cement and Kaolin clay treated with 5 and 10% cement, and the results are reported and discussed. The proposed model was evaluated by comparing its predictions with the triaxial test results reported on the cement-treated Ballina clay and Kaolin clay. The proposed constitutive model gave reliable predictions that agreed with the experimental results and captured the main features of cement-treated clays.

Because of the heterogeneous layered characteristics of geomaterials, analysis of tunnel stability may be complicated, and such characteristics increase the possibility of progressive failure of the surrounding rock banks. This paper offers an analytical upper-bound approach to the analysis of the progressive collapse of deep rectangular tunnels based on three-dimensional (3D) velocity discontinuity surfaces. A symmetric 3D rotational progressive failure mechanism that considers the presence of rock layers partly induced by weathering is initially proposed and analyzed with the upper-bound theorem. In this approach, the range and shape of potential falling blocks are determined with use of the variational principle and the partition optimization method. The results obtained with the proposed approach showed good agreement and consistency with existing literature. Sensitivity analysis was also conducted to assess the effects of relevant parameters on the scope of impending blocks. Such analysis can also shed light on the collapse mechanism at failure and can be applied to projects under stratified or deteriorated rock masses, areas in which studies are limited at present.

Leachate recirculation in municipal solid waste (MSW) landfills operated as bioreactors offers significant economic and environmental benefits. However, vertical well (VW) recirculation may not be an effective method because gravity will cause the recirculated leachate to flow directly downward to the leachate collection systems at the bottom of the landfill, resulting in a waste of recirculated leachate. One of the solutions to minimize the misapplication of leachate is to enable the leachate to flow in horizontal directions using combined spraying-VW systems, thus enabling it to flow through more MSW. The key objectives of this study were to investigate combined spraying-VW systems, to analyze the effects of applying spraying and VW recirculation systems simultaneously on the leachate migration in landfills, and to estimate some key design parameters (e.g., the steady-state flow rate, the influence radius, and the cumulative leachate volume). In addition, design charts for engineering application were established using a dimensionless variable formulation. The proposed design charts prove both simple and useful.

Richard’s equation governs the migration of moisture in the soil under unsaturated conditions. Although this differential equation provides a rigorous approach to simulating important infiltration problems, obtaining analytical and numerical solutions to this equation has been a particularly challenging task. This is largely due to the highly nonlinear nature of the soil hydraulic properties, including the moisture retention curve and the hydraulic conductivity function. Whereas analytical solutions of Richard’s equation have been reported for problems involving steady-state conditions and simple hydraulic models, solutions for transient conditions have rarely been obtained. However, such analytical solutions would be particularly valuable, for example, to validate the accuracy of numerical schemes, as well as to facilitate parametric evaluations. A series of analytical solutions of Richard’s equation for unsaturated flow under transient conditions have been developed as part of this study. The solutions involve a variety of initial and boundary conditions. The analytical solutions in this study could be obtained after expressing the governing equation as the addition of advective and diffusive flow components. The solutions consider logarithmic and linear models to represent the soil moisture retention and the hydraulic conductivity functions, respectively. Solutions are also provided for special cases in which either the advective or the diffusive components dominate the flow process, as well as for the steady-state cases. A parametric evaluation was found to provide insight into important characteristics of infiltration problems. In particular, relevant features of an unsaturated flow problem can be explained by evaluating the trends in its advective and diffusive flow components.

Although the finite-difference method (FDM) has been commonly used to numerically solve Richard’s equation, numerical difficulties are often encountered, even for comparatively simple problems. To minimize convergence problems, comparatively small discretization and time steps have often been adopted to solve this highly nonlinear equation, resulting in significant computational costs. To overcome these difficulties, this paper presents an efficient approach to solving Richard’s equation that combines two numerical techniques: the FDM and the cubic interpolated pseudoparticle (CIP) method. The FDM is used to solving the diffusive flow component of Richard’s equation, the convergence of which can be controlled by adopting time steps corresponding to Neumann’s number under 0.5. In contrast, the CIP method is used to solve the advective flow component of the equation. The CIP method is found to be particularly suitable for facilitating convergence and eliminating the presence of spurious results when the Courant number is under 1.0. Analytical solutions for transient unsaturated flow problems, developed in a companion paper, allow comparison between the predictions obtained using the proposed numerical approach and the exact solutions. Use of the newly developed algorithm is found to be particularly accurate and stable for solving Richard’s equation, being clearly superior to the use of the traditional FDM. After validating the new numerical approach using the boundary conditions and hydraulic functions for which analytical solutions have been developed, the new numerical scheme was subsequently implemented to address more general unsaturated flow problems. In particular, the new numerical approach was extended to solve unsaturated flow problems involving complex soil hydraulic functions as well as different boundary conditions. Comparisons are presented to illustrate the accuracy of the new numerical approach even when extended to incorporate the use of complex hydraulic functions for which there are no analytical solutions. The efficient, validated numerical schemes presented in this paper are found to be well suited for solving complex unsaturated flow problems.

In this paper, 62 centrifuge tests are collected from the literature and used to perform a statistical evaluation of the model factor for conventional methods to calculate the bearing capacity of dense sand overlying clay. The model factor is defined as a ratio of measured capacity to calculated capacity. The variations of the model factor with input parameters are established as regression equations based on the results of finite-element limit analysis (FELA). Conventional methods that multiply by regression equations are shown to be more accurate on average for all data sets. Further verification exercise from 27 additional centrifuge tests indicates the modified method could also be applicable for medium dense sand overlying clay. The mean and coefficient of variation of the model factor for the modified methods are finally characterized as a lognormal random variable with a mean of 1.06 and coefficient of variation of 0.17.

This paper investigates the distribution of intergranular forces within uncemented mine backfills using the discrete element method (DEM) and compares it with the existing analytical method. The virtual backfilling is modeled via the DEM to simulate the underground mining stopes backfilling with uncemented granular materials. Normal and shear forces of all particle contacts within the model backfill are tracked and analyzed with particular attention to the effect of sidewall friction. The DEM evaluates normal force chains and reveals a concentration of high forces within the model backfill. The DEM shows profiles of forces that are distinctly different from those obtained from analytical solutions. Quantitative analyses of the spatial distribution of forces, number of contact points, and changes in the orientation of forces are presented. The DEM demonstrates its capacity as a good tool for looking closely into the backfill on a particle scale. It highlights potential force distribution and concentration within a backfill and shows the limitations of analytical solutions, which helps engineers in the mining industry to better understand the possible mechanisms within backfill.

Terzaghi proposed a two-dimensional (2D) formula for arching based on the assumption of a vertical sliding surface induced in the upper part of soil mass attributable to the downward movement of a trapdoor. This study expands the 2D Terzaghi arching formula to a three-dimensional (3D) formula in which inclined sliding surfaces under general 3D excavation conditions are considered. The effects of the formula under various conditions were investigated. The assumption of the original 2D formula that the maximum shear strength is mobilized on a vertical surface is different from reality, because an actual sliding surface caused by downward movement of a trapdoor is an inclined surface. Furthermore, the 2D Terzaghi formula is limited to conditions of plane strain and does not consider 3D excavation conditions. Therefore, to examine the practical effects of these issues and to consider the arching effect in 3D excavation conditions, a formula was developed to expand the Terzaghi arching formula to inclined sliding surfaces under downward movement in 3D conditions. Using the expanded formula, the effects of excavation, ground, and surcharge conditions on vertical stress were examined, and the results were compared with those of the 2D Terzaghi formula. The induced vertical stress was highly affected by the inclination angle and the longitudinal excavation length. The degree of influence depended on the excavation, ground, and surcharge conditions. It is expected that the results from this study will provide a better understanding of various arching phenomena in the future.

A simple version of a recently proposed anisotropic elastoplastic bounding surface model was used to simulate the mechanical behavior of natural Shanghai soft clay. The characteristics of stress–strain curves attributable to structural deterioration were approximately simulated by the model using a lower-level parameter s for the elastic nucleus. Successful simulation was achieved because, from the viewpoint of engineering applications, the bounding surface is equivalent to the structure surface, and the elastic nucleus is approximately equivalent to the reference surface. The model was expressed with a total of nine parameters. Simulations were carried out on isotropically and anisotropically consolidated specimens with varying preconsolidation pressures under undrained conditions and on stress-probing tests from the in situ stress states under drained conditions. The simulations were found to be satisfactory compared with the test results. Thus, the possibility of simulating natural clays with low to medium sensitivity using a simplified version of the bounding surface model with a carefully defined elastic nucleus was demonstrated.

The three-dimensional (3D) stability calculations of soil slopes are often focused on homogeneous soils in the published literature. However, strength inhomogeneity is a common phenomenon in slope engineering. The purpose of this paper is to investigate the influence of strength inhomogeneity on the seismic and static 3D stability of a two-stage slope. The soil is inhomogeneous in the vertical direction only, and the slope is subjected to the horizontal earthquake force. Using a 3D failure mechanism, the internal energy is only dissipated along the sliding surface. The external rate of work is done by the soil weight and the earthquake force. Based on the upper bound theorem of limit analysis, the slope stability problem is formulated as a classical nonlinear programming problem. Coding the corresponding computer program, the stability factors of inhomogeneous soil slopes are obtained. When the inhomogeneous coefficient is zero, the present results are compared with those previously published solutions. Based on the comparisons, the approach of this paper is effective for estimating the 3D stability. A study is conducted to investigate the effects of the inhomogeneous coefficient on seismic and static stability factors of a two-stage slope.