International Journal of Geomechanics

Experiments were carried out using a dynamic hollow-cylinder apparatus (HCA) to investigate the effects of stress paths and principal stress rotations experienced during a simple vertical excavation on the element-scale deformation and noncoaxial behavior of a highly angular granular material. For this purpose, an improved specimen preparation technique was used to generate homogeneous HCA specimens using a multilayer undercompaction method. The stress paths used in the HCA experiments were extracted from the numerical results obtained in a discrete element simulation of a simple vertical excavation, where complex stress paths and principal stress rotations have been observed. The experimental results show that different stress paths and rotations in excavation significantly affect the element-scale deformation behavior. Noncoaxial behavior (i.e., the deviation of plastic strain increment direction from the principal stress direction) was observed in the HCA tests, which was a result of the combined effects of stress history, mean stress, deviator stress, and principal stress rotation. The deviator stress seems to have a more apparent effect than the mean stress on noncoaxial behavior. The experimental data will be useful in understanding the basic behavior of lunar soil under excavations because both materials share the similar macroscopic and microscopic characteristics.

It is assumed that rocks contain three-dimensional (3D) penny-shaped microcracks. The Mode II and III dynamic stress-intensity factors at the tips of 3D penny-shaped microcracks are determined. The orientation angle of microfailure in rock materials is obtained to describe the dynamic failure of rocks. The relationship between the microfailure orientation angle and stress components is derived from the dynamic fracture criterion. Failure-characteristic parameters of penny-shaped microcracks under dynamic triaxial compressive condition are defined; these are an invariant. A 3D nonlinear dynamic strength criterion of rocks is established using the micromechanical method. The 3D nonlinear strength criterion is novel, and is not found in the existing literature. By comparison with experimental data, it is shown that the present 3D dynamic strength criterion is in good agreement with the experimental results.

This paper investigates slope stability and produces a set of stability charts for three-dimensional (3D) slopes for a specific case in which frictional fill materials are placed on purely cohesive clay. As slopes are not usually plane strain in nature and are influenced by physical boundaries, this study uses a 3D analysis using the finite-element LB limit analysis method. Stability charts are convenient tools for geotechnical engineers during design in practice. For comparison purposes, the results from two-dimensional (2D) analyses are also discussed. The results from this study quantify the increase in the factors of safety obtained when 3D conditions are analyzed as opposed to the more traditional 2D.

The constant shear drained (CSD) test is considered an appropriate test to simulate the instability behavior of soils in slopes under water infiltration conditions or lateral stress relief. However, contradiction of the drained instability in loose granular material exists in the reported test results, which is considered because of the condition of constant deviatoric stress ($q$) not strictly satisfied in the literature. Because the variation of $q$ during the CSD test has significant effects on the test results, more data from tests under a true constant $q$ condition are needed to clarify this subject. In this paper, CSD and conventional undrained triaxial tests in both compressive and extensive loading were performed to investigate the instability behavior of loose sand. All the CSD tests were conducted by advanced variable confining pressure triaxial apparatus, in which a true constant $q$ was maintained during the test; thus, more reliable results were obtained. It is observed experimentally that when a specimen is sheared along a fully drained stress path with a constant $q$ but decreasing effective mean normal stress, instability occurs before the effective stress path reaches the failure line. It is also found that the onset of instability for both undrained and CSD tests are initiated at almost the same stress ratio for a given void ratio of specimens. Hill’s stability conditions in terms of the sign of the second work increment are used to interpret the experimental results of instability. The high-quality test results obtained in this study may help to explain the contradiction reported in the literature and clarify the controversy in drained instability.

Estimation of safe bearing capacity (SBC) of noncohesive soil based on Indian Standard Code requires a lot of field work, viz, conducting direct shear tests to determine cohesion and angle of internal friction, performing the standard penetration test to determine the $N\text{-value}$ of soil, and finding the relative density and dry density of soil. The present study does away with these soil parameters except for the design value of density and uses the results of sieve analysis to determine the SBC of soil. This research proposes the use of artificial neural network (ANN) to predict the SBC of noncohesive soil as a function of coefficient of curvature, coefficient of uniformity, and design value of soil density along with footing dimensions such as depth, width and diameter (in case of circular footing), and the desired settlement of the footing. The results show that ANN is a useful technique in estimating SBC of noncohesive soil using parameters derived from sieve analysis results and match closely from the results derived from the traditional methods based on Terzaghi’s theories.

The aim of this paper is to investigate the propagation of Love waves in an anisotropic fiber-reinforced layer over an elastic inhomogeneous stratum. The inhomogeneity of the half-space has been taken as a linear variation of rigidity and density. The equations of motion have been formulated separately for layer and half-space under suitable boundary conditions. The frequency relation of phase velocity has been deduced in compact form using separation of variables by means of the Whittaker function. Some particular cases have also been investigated. As a special case when both the layer and half-space are homogeneous, the computed frequency relation coincides with the general equation of the Love wave. Numerical calculations of frequency relation have been performed for different values of parameters and plotted graphically to study the effect of different factors. The wave velocity is strongly influenced by the reinforcement and inhomogeneity parameters.

During many earthquakes, soil liquefaction causes dramatic damage. The use of a granular column is a ground-improvement technique used to mitigate soil liquefaction. The present paper studies the performance of reinforcement with granular columns as a method for mitigation of potential risk of liquefaction during cyclic loading. The generation and dissipation of excess pore pressure are analyzed by considering the granular-column installation effect. This effect is described by a decrease in horizontal permeability within a disturbed zone around the column, which is described by constant, linear, and parabolic variations. The evolution of excess pore pressure is studied as a function of the disturbed zone in terms of reduced horizontal permeability. Obtained results show that a granular-column installation has a significant influence on the mitigation of liquefaction.

Pullout resistance of cement-grouted soil nails is a key factor affecting the safety conditions of retaining walls, slopes, and excavations. The mobilized frictional resistance at the interface between soil nails and surrounding soils depends on various parameters such as saturation ratio, water content, grouting under gravity or pressure, etc. The interface roughness condition between soil nail and soil is a critical factor but difficult to control in both laboratory and field owing to technical difficulties in creating a rough drillhole surface. The present study focuses on the pullout behavior of model soil nails with different interface roughness conditions in the laboratory to establish quantified correlations between frictional resistance and roughness angles of internal drillhole surface. Cross-sectional shapes of internal drillhole surfaces were created using four plastic rods with various shapes of external threads (four different values of roughness angles). Measured peak values of pullout resistance of soil nails with rough drillhole surface were compared with the soil nails with smooth drillhole surface. The present test results were verified with a previous analytical model, which considered the soil dilation to be an important factor influencing the pullout resistance of soil nails. Test results also indicate that the peak pullout resistance increases almost linearly with an increase in roughness angles. In addition, the pullout resistance values decrease approximately linearly with an increase in pullout displacement after peak pullout resistance is approached. The soil-nail diameter values of the soil nails with rough drillhole surfaces expanded substantially after being pulled out of the ground. This leads to a substantial increase in pullout resistance of soil nails.

In cylindrical coordinates, a potential method is developed for three-dimensional (3D) wave propagation in a poroelastic medium. By using the proposed potential method, the wave propagation problems can be reduced to the determination of four scalar potentials governed by four scalar Helmholtz equations, representing the motions of $P1$, $P2$, $\mathit{SV}$, $\mathit{SH}$ waves in the porous media, respectively. By the methods of separation of variables, the general solutions to those Helmholtz equations are found in cylindrical coordinates. Boundary value problems associated with a homogeneous poroelastic half-space loaded by surface tractions, that is, Lamb’s problem for a fluid-saturated medium is resolved using the obtained general solutions. It is shown that these potentials introduced in this research for 3D wave propagation problems can also be reduced to those reported by previous researchers for axisymmetric wave propagation in the fluid-saturated porous medium. Furthermore, numerical examples for the state–state and transient responses of the poroelastic half-space are provided.

This paper presents a critical state constitutive model for cemented sand. The model uses a single capped yield surface as a function of the void ratio, confining pressure, preconsolidation pressure, and stress ratio at the peak of the undrained effective stress path. To model the cemented materials, the formulation of the yield function, elastic moduli, plastic modulus, flow rule, and other components of the model have been modified. Having incorporated the tensile strength and cohesion, the radial-mapping formulation of the bounding surface plasticity is incorporated in the model. The modified model has been calibrated and verified based on experimental results.

The present paper deals with the propagation of torsional surface waves in an anisotropic porous layer over an inhomogeneous dry sandy half-space. The shear modulus of elasticity and density has been considered as variable in a porous layer, and the modulus of rigidity remains variable in a sandy half-space. The Whittaker function and its derivative give the result of the phase velocity equation using suitable boundary conditions. The effect of a dimensionless wave number on a dispersion curve has been found numerically, and a graphical representation of porosity and sandiness has been given. The derived dispersion equation found that the velocity of a torsional wave is influenced because of the presence of porosity, inhomogeneity, and sandy half-space. The study may be useful to understand the nature of seismic-wave propagation during earthquakes.

Previous experimental studies on laterally loaded pile groups usually applied loading along the direction parallel to the edge of the pile cap. This study aims to determine the effects of the loading direction on the response of laterally loaded pile groups through a comprehensive experimental investigation. Model pile groups with different configurations embedded in sand were subjected to lateral loads along various horizontal directions. The results show that the loading direction has a predominant effect on the evolution and eventual distribution of force among piles in the pile group, the bending responses along the piles, and the total lateral resistance of the pile group. These results can be attributed to different group-interaction effects under different loading directions. For both square and rectangular configurations, the pile groups provide the largest total lateral resistance along the diagonal direction. The effect of the loading direction on the response of the pile group is affected by the configuration of the group. The pile group at medium spacing ($5D$) is more sensitive to changes in the loading direction. Back-calculated $p\text{-multipliers}$ indicate a substantial difference in $p\text{-multipliers}$ of individual piles when the pile groups are loaded along different directions. The $p\text{-multipliers}$ of the front-row pile can be approximately 67% larger when loaded along the diagonal direction than when loaded along the direction parallel to the edge of the pile cap. The effects of both the pile group configuration and the loading direction on the values of $p\text{-multipliers}$ should be considered in analyzing the responses of pile groups under lateral loads.

During consolidation, excess pore-air and pore-water pressures are forced to dissipate through permeable boundaries. This dissipation process inevitably results in the reduction of the soil volume, and thus settlement. Such a phenomenon can be mathematically described by inhomogeneous governing equations of flow according to Fick’s (with respect to air phase) and Darcy’s (with respect to water phase) laws. This paper discusses the dissipation of excess pore-air and pore-water pressures and settlement of an unsaturated soil layer subjected to various time-dependent external loadings. An analytical solution is derived from the governing flow equations with respect to air and water using eigenfunction expansion and Laplace-transform techniques. Eigenfunctions and eigenvalues are parts of the general solution and can be obtained using one-way or two-way drainage boundary conditions. On the other hand, four types of external loadings, namely ramping, asymptotic, sinusoid, and damped sine wave, are mathematically simulated and incorporated in the mathematical procedure. Once the time variable ($t$) in partial differential equations is transformed into the Laplace complex argument ($s$), generalized Fourier coefficients can be obtained by taking a Laplace inverse, and eventually the final solution can be obtained. The consolidation behavior of the unsaturated soil subjected to the previously mentioned types of time-dependent loads will be presented in separate examples. Additionally, the permeability ratio ($k_a/k_w$) and the loading function parameters influencing changes in dissipation rates of excess pore pressures and settlement are investigated and discussed in this paper. It is observed that the increasing permeability ratio and loading parameters have significant effects on the change in the pore pressures.

Evaluation of the uplift capacity of plate anchors in saturated clay is an important aspect in the design of offshore foundation systems of various structures. In most of the literature reviewed, simple constitutive models such as Tresca or Mohr–Coulomb (MC) have been used in evaluating the plates’ pullout capacity. There exists a need to study the pullout capacity of anchors using other advanced soil models and explore differences in computed behavior. In addition to the MC model, two other constitutive models are used herein to represent the soil behavior. These are Modified Cam-Clay and Soft Soil models. A series of finite-element analyses are performed using the three constitutive models. Undrained effective stress analyses are conducted to study the response of both strip and circular plate anchors in saturated soils. The capacities of plate anchors are assessed through the application of the displacement control approach. The effective stress parameters are correlated with the undrained shear strength, and $N_c$ (dimensionless breakout factor) values from the three constitutive models are presented and compared with the lower bound solution, as well as with the data obtained from similar studies and experimental data available in the literature. Differences resulting from the characteristics of the three constitutive models are examined and discussed.

Once a slope is led to the limit equilibrium state using the strength-reduction method, the displacement contours located near the critical slip surface are quite close. The critical slip surface is composed of the points at which the directional derivative of displacement along the direction perpendicular to the critical slip surface arrives at the maximum in the vertical direction. First, a series of vertical lines are evenly set up along the horizontal direction, and some discrete points are arranged along each vertical line. Then, for each vertical line, the directional derivative of displacement along the direction perpendicular to the critical slip surface of the middle position of any two adjacent discrete points is calculated using the central difference method. Next, the point with the maximum directional derivative of each vertical line is determined, and each point smoothed by the least squares method could characterize the position of the critical slip surface. Finally, two examples are executed to verify the reliability of the proposed method.

A geotextile tube is a type of geocontainer typically filled with sandy slurries and fine-grained dredged sediments. Its performance in strength, dewatering, fine-particle retention, and stacked stability has been studied extensively. However, very little is understood about the shape-deformation behavior of geotextile tubes. In this paper, slurry-settlement, constant head permeability, and seepage-force tests were conducted to determine the geocontainers’ geotechnical design parameters. The characteristics of the dredged fill material determined from the slurry-settlement, constant head permeability, and seepage-force tests are presented. Large-scale tests on model geotextile tubes were also conducted. A large-scale apparatus for geotextile tube–filling test simulation is introduced. The apparatus consists of a slurry mixing station, a pumping and delivery station, a geotextile tube–filling station, and a data station. The results of the model tests conducted on a transparent geobag (undrained condition) and a geotextile tube (drained condition) are presented in this paper.

Heger pressure distributions are considered a fundamental tool in the design of RC culverts, according to the direct-design method. However, some factors known to affect soil–structure interaction are neglected when using Heger pressure distributions. These factors include the effect of the trench geometry, the relative stiffness of the existing soil to the backfill, and the burial depth of the structure. This paper presents a detailed finite-element analysis parametric study that investigates the accuracy and applicability of Heger pressure distributions for culverts in partial trench installations when the aforementioned factors are considered.

Problems involving fluid flow in porous media are of great interest in many scientific and technological areas. The development of numerical methods at the pore level allows simulating such phenomena considering characteristics and heterogeneities of the medium normally ignored in the macroscopic approach. To achieve the computational implementation of those numerical methods, it is necessary to initially define the domain (porous media) in which the simulations will be held. In this study, a simple, yet powerful methodology of representing a porous medium by means of cellular automata (CA) and microcomputed tomography is presented. Two parameters are proposed to link the tomographic images with those generated by CA. The first one considers the porosity, whereas the second one takes into account void alignment inside the image. The methodology computes the parameters in every automata image generated in a time range and compares them with the parameters of the tomographic image until certain user-controlled precision is achieved. As an application example, two tomographic experiments with different resolutions were carried out on a soil sample. Two-dimensional (2D) outer totalistic CA rules whose evolution in time exhibits variation between the amount of black and white cells, independently from the initial condition, are considered. The calculations showed a gain of accuracy with the resolution increase. Although the implementation is presented for the 2D case, the methodology proposed is easily extendible to three-dimensional analysis.

The fluctuations of reservoir water levels significantly change the hydrogeological conditions of reservoir banks and thus affect the steady state of the bank slope. Reservoir landslide stability is governed by the complex interactions between the rock and the water (both reservoir and pore water). This paper establishes the constitutive coupled model of seepage and stress field for the E20 bank slope in the Haizhou Open Pit Coal Mine hydropower station’s lower reservoir. Using the geotechnical engineering three-dimensional fast Lagrangian analysis of continua (FLAC-3D 4.0) program as a computational analysis tool, the E20 bank slope deformation mechanism was analyzed. The simulation model, calculated by using the Boit consolidation and pore-water continuity principles, was built using FEMs. The numerical simulation results showed that cyclical fluctuations and speeds of the reservoir’s water level affect its bank slope stability. When the water level drops at a speed of 12 m/day, the simulation’s calculated safety factor value is 0.99, but when the water level rises at a speed of 12 m/day, the calculated safety factor value is 1.03. The results demonstrated that the rapid drop of the water level had a greater impact on the reservoir bank slope stability than the rapid rise of the water level under the same conditions.

A suite of laboratory testing was performed on Gosford sandstone samples having a range of sizes, including point-load and uniaxial compressive tests. A unified size-effect law (USEL), based on the work by Zdenek Bazant, involving fracture energy as well as fractal theories, was introduced. It was shown that USEL correlates well with the ascending and descending uniaxial compressive strength trends obtained from Gosford sandstone as well as five other rock types reported by Brian Hawkins. Fractal characteristics found to be the primary mechanism for ascending strength trends and surface flaws could be considered as a secondary mechanism. The influence of the contact area on the size-effect behavior of point-load results was investigated using a new approach. This approach was novel in the way it incorporated the load contact area. Determination of the point-load strength index using this new approach led to opposite size-effect trends compared with those observed using a conventional point-load strength index. Hence, the utilization of USEL leads to better simulation of the new point-load strength index data.

The present problem analytically investigates the possibility of Love-type wave propagation in a prestressed irregular composite layer lying between an upper prestressed heterogeneous isotropic layer of finite width and a lower prestressed isotropic half-space. The closed-form expression of dispersion relation has been deduced and matched with the classical Love wave equation as a special case of the problem for its authenticity. The effects of size of irregularity, heterogeneity parameter of the uppermost layer, width ratio of layers, and horizontal prestresses, present in each of the media, on the dispersion curve are the prime outcome of the study. A comparative study made between the case in which a composite medium is present as an irregular sandwiched layer and the case in which an isotropic medium is present as an irregular sandwiched layer is one of the major highlights of the problem. Moreover, numerical computations have been carried out and are depicted by means of graphs.

In this paper, a full vehicle–track–ground coupling model is presented to evaluate the dynamic response of the subgrade due to high-speed trains. The vehicle was modeled as a multibody. The track was considered as an Euler beam. The ground soil was regarded as two elastic layers and a poroelastic half-space, taking into account a complete subgrade/subsoil system. The wheel–track interaction was considered by using the linear Hertzian contact theorem. The stiffness matrix method and the Fourier transform were introduced to deal with formulations of the coupling model in a transformed domain, and the time-domain solutions were derived by using the fast Fourier transform algorithm. The wheel–track contact forces and the dynamic responses of the subgrade were studied, and the effects of the rail irregularity and the properties of the subgrade bed were then investigated. It was concluded that the dynamic responses of the subgrade are significant compared with responses induced by the axle load and are influenced greatly by rail irregularity and parameters of the subgrade bed.

This paper aims to investigate the propagation of Love-type waves in the double layers lying over an isotropic homogeneous half-space. The two layers have been considered of finite width and a different sort of heterogeneities. Debye asymptotic expansion has been used to obtain the closed form of the dispersion equation. It has been found that the heterogeneity and width ratio of layers have a considerable effect on the phase velocity of Love-type waves. In particular, increment in the width ratio decreases the phase velocity of Love-type waves. The established dispersion relation for this study agrees well with the classical results. The comparative study of the present problem with a case in which double layers are homogeneous has been made. Results have been represented graphically, and it has been observed that the dimensionless phase velocity decreases with the increase in dimensionless wave number. It has also been examined that the heterogeneity parameter of uppermost layer and intermediate layer affects the phase velocity substantially.

This paper presents a semianalytical solution for axially loaded pile groups in multilayered, linear-elastic soil profiles. The piles in the group can have circular, square, or rectangular cross sections. The soil displacement surrounding a pile group is linked to the axial displacement experienced by each of the piles in the group. The method is based on assigning a displacement decay function to every pile in the group and then summing up for all piles in the group the product of the axial displacement of each pile and its associated decay function. The governing differential equations describing the response of the soil and piles are derived by applying the principle of virtual work and calculus of variations to the pile–soil system. The governing differential equations predicting the response of the piles are solved analytically using the method of eigenvalues and eigenvectors, whereas the differential equations describing the soil decay functions are solved numerically using the finite-difference method. The method produces displacement fields that are very close to those produced by the FEM but with less computational effort.

A numerical model, called CST3 (Consolidation and Solute Transport 3), is presented for coupled one-dimensional large strain consolidation and solute transport in layered soils. The consolidation algorithm accounts for vertical strain, soil self-weight, general constitutive relationships, relative velocity of fluid and solid phases, changing compressibility and hydraulic conductivity during consolidation, unload/reload, time-dependent loading and boundary conditions, external hydraulic gradient, variable preconsolidation stress profiles, and multiple soil layers with different material properties. The solute transport algorithm accounts for advection, diffusion, mechanical dispersion, linear and nonlinear sorption, equilibrium and nonequilibrium sorption, porosity-dependent effective diffusion coefficient, and first-order decay reactions. CST3 is based on a dual-Lagrangian framework that separately tracks the motions of fluid and solid phases. The development of CST3 is first described, followed by verification checks. Numerical simulations indicate that layered soil heterogeneity and preconsolidation stress can have important effects on consolidation-induced solute transport behavior. Failure to correctly account for soil heterogeneity or preconsolidation stress profile can lead to significant errors in the analysis of consolidation and solute transport in layered soils.

Often granular materials are stored in vertical containers with circular or square cross sections. The storage material can be food grains, pharmaceutical powders, chemical pellets, or geomaterials such as mine fills. The design and analysis of these containers require adequate knowledge of the stresses developed within the filled material. The stress isobars developed herein enable the designers to estimate the vertical stress at any point within the fill contained in a silo. The same isobars can also be used for square cross sections, as in the case of backfilled underground mine stopes, without sacrificing the accuracy much. The same method was previously followed by the authors in developing isobars for plane-strain situations. On the basis of the two sets of isobars for trenches and square stopes, it is possible to interpolate the stresses for other rectangular mine stopes, which can serve as good first estimates in the designs.

Assuming that the water content and hydraulic conductivity of unsaturated soil are exponential functions of the pressure head, Green’s function is used to obtain analytical solutions to one-dimensional coupled rainfall infiltration and deformation in unsaturated soils under varying surface rainfall flux. The analytical solution considers varying flux and pressure head at the top boundary and arbitrary initial conditions. In particular, nonlinearly increasing rainfall intensity at the surface boundary is considered. The result indicates that the coupling of seepage and deformation has a significant effect on the pressure-head profiles for the transient unsaturated seepage. The coupling effect is closely related to the boundary conditions. The coupling effect almost disappears if ponding at the ground surface occurs. The ponding time is different under the coupled and uncoupled conditions. There is a quick change in the pressure-head profiles near the time of ponding or peak or discontinuous rain intensity.

Soil arching in the reinforced piled embankment is investigated in this paper on the basis of two case studies of high-speed railways constructed in the eastern coastal region of China. The majority of the overburden load was found to have been transferred from the soil to the pile because of soil arching in the piled embankment. In addition, the critical height was approximately 2.6–3.8 times the net pile spacing. The adapted Terzaghi method, the BS8006 method, the Hewlett and Randolph method, EBGEO, and a simplified analytical method used to analyze the reinforced piled embankment were discussed and verified by the two cases. It was found that the adapted Terzaghi method was consistent with the measurement for the stress reduction ratio, with an error of 2.0–38.0%. The simplified analytical method predicted the maximum geogrid strain with the error of 6.7–33.2%, and assessed the maximum settlement at the subsoil surface with an error of 4.4–51.0%.