International Journal of Geomechanics

This study investigated the uplift resistance of strip anchors embedded in cohesive frictional soils or rocks exhibiting zero or low tensile strength. Uplift resistance was estimated on the basis of the upper-bound theorem of the limit analysis assuming that the ground obeys the Mohr–Coulomb failure criterion with or without tension cutoff. Calculus of variations was used to assess the geometry of the failure surface. The effects of geometrical and geotechnical parameters on the uplift pressure were systematically analyzed, particularly the effect of the tensile strength, which has not been investigated in the literature to date. Comparative computations show that the solution presented gives results similar to those of numerical stress analyses and improves on existing upper-bound solutions because it provides a lower value for the upper bound of the uplift resistance under the realistic assumption of negligible tensile strength. The improvement is small for soils but significant for rock masses, where neglecting the tension cutoff would lead to a false presupposition of considerable tensile strength.

Dynamic shear modulus plays an important role in the seismic assessment of geotechnical systems. Changes in the degree of water saturation influence dynamic soil properties because of the presence of matric suction. This paper describes the modification of a suction-controlled cyclic triaxial apparatus to investigate the strain-dependent shear modulus of unsaturated soils. Several strain- and stress-controlled cyclic triaxial tests were performed on a clean sand with various degrees of saturation. Suction in unsaturated sands increased the shear modulus in comparison with the ones in dry and saturated conditions for different shear strain levels, with a peak modulus in higher suction levels. Also, shear modulus decreased with an increase in the shear strain for specimens with similar matric suction. The normalized shear moduli of the unsaturated sand specimens followed a similar trend to the ones predicted by the available empirical shear modulus reduction functions but showed lower values. The modulus reduction ratios of unsaturated sands shifted up as a result of higher effective stress and suction-induced stiffness. These trends were consistent for both strain- and stress-controlled tests.

A complete and accurate method for determining the stresses and displacements of a lined arbitrary shaped tunnel excavated in orthogonal anisotropic rock mass is proposed. The method is based on an analytical method, the complex variable method, and the power series method. The basic equations can be obtained according to the stress boundary conditions along the inner boundary of the lining and the stress and displacement continuity conditions along the lining–rock interface. Based on the method, the tangential stresses along the excavation boundary, the inner and outer boundaries of the lining, and the normal and shear stresses along the lining–rock interface are given. Results show that, when the number of terms of the series is large enough, solutions with high accuracy can be obtained. The positions of the tangential stress concentration, the effect of the displacement release coefficient, and the angle of the rock layers on the tangential stresses along the excavation boundary and both boundaries of the lining are discussed.

Estimation of the thermal regime (i.e., the variation of soil temperature, θ, and heat flux, ϕ) in soil mass is a key issue in the realms of agronomy, forestry, ecology, micrometeorology, and geotechnical engineering. Usually, it is predicted by solving heat-conduction equations (HCEs) numerically and/or analytically by imposing assumptions such as (1) the sinusoidal variation in temperature (caused by the change in the ambience as a result of the solar cycle) at the top soil surface and/or (2) the uniform initial temperature of the soil mass. However, these solutions sometimes yield an improper thermal regime because of simplified assumptions that are not always suitable for natural soil surfaces. In this paper, the novel algorithm ATHERES (algorithm for thermal regime estimation in soils), which can be used for predicting thermal regime in sandy soil mass, is presented. The proposed approach eliminates the necessity for solving the HCE, and thus, the obtained thermal regime in sandy soil mass is free from the assumptions associated with conventional approaches. Performance of the proposed approach was demonstrated by using the results obtained from a series of laboratory tests on sandy soils of different particle sizes. The study reveals that the ATHERES is capable of incorporating naturally occurring temperatures and flux boundary conditions, including the initial condition of a nonzero thermal gradient.

This paper presents a solution for cavity expansion in strain-softening and undrained soil mass based on the unified strength failure criterion. Stress distribution around the cavity expansion was divided into three regions (i.e., elastic, softening, and plastic flow zones). The deformation was assumed to be governed by the small strain in the elastic zone and the large strain in the softening and plastic flow zones, and a closed-form solution of the stress and strain was obtained for the different zones. Moreover, the softening zone radius, the excess pore-water pressure in the plastic flow zone, and the ultimate cavity expansion pressure were obtained for cavity expansion in the strain-softening soil mass by incorporating certain factors, such as large strain, drainage condition-, and intermediate principal stress. Furthermore, several cases were analyzed using the proposed approach. The results of the ultimate cavity expansion pressure (e.g., k = 1) were consistent with those obtained through previous theories and local tests.

In this paper, a Newton conjugate gradient (Newton-CG) augmented Lagrangian-based finite-element method is proposed to solve elastic contact problems without friction. The contact problem is discretized by the finite-element method. Based on a minimum theorem, the contact problem is reformulated as an optimization problem with inequality constraints. Then, the Newton-CG augmented Lagrangian method is applied to solve the constrained optimization problem. Numerical experiments were performed to validate the efficiency of the proposed method.

Previous studies have usually idealized the boundary conditions of unsaturated soil as absolutely permeable or impermeable. However, this assumption is not sound for the majority of cases where the boundary is partially permeable. In this study, partially permeable conditions are described using exponential functions for the excess pore-air and pore-water pressures at the boundaries. A generalized analytical solution for the consolidation of unsaturated soil under these proposed boundary conditions and constant initial excess pore-air and pore-water pressure conditions were obtained. The results of the proposed solution agreed with an analytical solution available in the literature, which verifies the feasibility of this study. The proposed solutions were subsequently tested and compared to published experimental data. Furthermore, a new concept, degree of drainage, was developed to characterize the partial-drainage conditions at the boundaries. Finally, a parametric study was carried out to show the consolidation characteristics under different degrees of drainage and ratios of hydraulic conductivities of air and water phases. The excess pore-pressure dissipation processes at the boundaries and the average degrees of consolidation for both the air and water phases are presented and discussed.

The effectiveness of vacuum preloading is a very important aspect of the improvement effect of dredger fill. This study experimentally investigated this issue using four different vacuum-preloading methods with a physical model test. The ultrasoft soil was obtained from Tianjin, China, and the samples were prepared in a slurry state using a physical model testing device. The samples were subjected to the traditional vacuum-preloading method and three modified vacuum-preloading methods (multistaged vacuum preloading, vacuum preloading with intermittent ventilation, and vacuum preloading with air injection and intermittent ventilation), in which the water discharge amount, rate of water discharge, amount of settlement, and pore-water pressure were analyzed as well. The results indicate that, under the vacuum preloading with air injection and intermittent ventilation mode, the water discharge amount increased faster, and the final discharge volume was greater than that obtained under the other methods. Meanwhile, the variation trend characterizing the settlement was similar to that of the water discharge amount, where the relative settlement under the vacuum preloading with air injection and intermittent ventilation mode was approximately 1.8 times that under the traditional vacuum-preloading method for the Tianjin hydraulic fill foundation. In addition, the results for the water content and dry density indicated that the vacuum-preloading method with air injection and intermittent ventilation was more effective than the other vacuum-preloading methods in terms of improvement in the Tianjin, China, area.

During the last decade, extensive research has been performed to improve shear strength models. Improvements in accuracy are the result of accounting for measurement errors of the cone penetration test with pore-water pressure measurement (CPT_u), reducing uncertainties in testing procedures, applying methods of reliability analysis, and accounting for the variability in the soils. Generalized equations always reflect some error due to site-specific conditions (e.g., stress history, geologic conditions, variability in soils). CPT_u data and consolidated undrained triaxial test data were used here to develop a CPT_u-based model that can accurately predict the effective shear strength of clay. Measurements of fat clay with Coastal Plain sedimentary origin were used. Two alternative shear strength models were developed: one based on the concepts of the Mohr-Coulomb strength theory, which is referred to as the theoretical model, and one developed for the effective friction angle and the effective cohesion to estimate the shear strength. The second model is referred to as the parametric model. Both shear strength models showed good agreement with the measured data. The data and models were used to develop tolerance limits and confidence intervals for both shear strength alternatives. A comparison of available empirical model forms and the proposed models are also presented. To assess the uncertainty of shear strength estimates, a methodology based on fuzzy logic was used.

The convergence-confinement method (CCM) applies to circular tunnels in in situ stress fields in which all three principal stresses are equal and the rock mass exhibits elastic-perfectly plastic shear failure. As radial wall displacement cannot be obtained easily using analytical methods, extensive parametric analysis of bidimensional numerical modelling to investigate the strain of the shaft wall close to the excavation bottom was performed. In all, 81 cases were derived from combinations of geometrical parameters and three weak rock categories. Through processing data relating to values of u_R0 (radial displacement of the shaft wall at the excavation bottom) obtained by numerical calculation in the different cases studied, it was possible to calculate the u_R0/R ratio as a function of the lithostatic stress p₀, the lining thickness s, and the shaft radius R. Novel equations were obtained to quickly estimate the value of u_R0 given the thickness of the lining concrete, the shaft depth, and the shaft radius for the qualities of rock considered.

Hydraulic fill is often used to fill large underground voids created during mining operations. It is produced and distributed as a slurry at a pulp density (P) of 65–75% (solids content). Consequently, a substantial amount of water needs to drain after placement. Inadequate drainage has been regarded as the main cause of barricade failure for stopes with hydraulic fills. Therefore, a good understanding of the evolution of total and effective stresses within such backfilled stopes is critical for barricade design. Most existing analytical solutions for assessing stresses in stopes are based on Marston’s approach by considering a fully drained (without pore-water pressure) or hydrostatic state. These conditions are not always representative of the stress state in stopes and behind barricades. When slurried hydraulic fill is placed into a stope, the self-weight consolidation or sedimentation of the fill can take place fairly rapidly. Ponding could first occur on the top of backfill if the drainage through barricades is not sufficient. Drainage through the barricade then allows the water table to descend, changing the pore-water pressures with time. In this paper, the authors present analytical solutions for estimating the evolution of water table and pore-water pressures in stopes with submerged hydraulic fills. These solutions were validated using numerical simulations. The results show that the ponding on the top of the settled fill has a negative impact on the barricade safety. Two-dimensional (2D) modeling without considering the reduced drift area tends to underestimate the pore-water pressures in stopes and behind barricades, which may render the barricade design nonconservative. Discussion follows on some particular features and limitations of the proposed analytical and numerical solutions.

Extensive studies of pile barriers have been published in recent years. However, one important item in particular has been overlooked: the attenuation properties of multiple rows of piles embedded in fluid-saturated poroelastic soils. This paper investigates the propagation and attenuation of plane waves in fluid-saturated poroelastic soil by multiple rows of piles. First, the attenuation zones of a two-dimensional (2D) periodic structure consisting of piles and saturated soil are studied on the basis of the periodic theory of solid-state physics. The effects of physical parameters, such as the density and elastic modulus of soil, and geometric parameters of pile barriers on the attenuation zones are investigated comprehensively. Second, a numerical analytical model for ambient vibration attenuation using pile barriers is built, and the response analysis is performed in the frequency domain. Results of the present investigation provide a new concept for designing pile barriers to block midfrequency vibration in fluid-saturated poroelastic soil.

Pipe roof is a commonly used prereinforcing measure for stabilizing tunnel arches during tunneling in portal sections or passing beneath important facilities. This paper presents an investigation on the mechanical performance of a large-scale pipe roof (the pipes are 85 m long and 159 mm in diameter) that was used to prereinforce the surrounding ground and improve the stability of the Shitougang Railway Tunnel, which passes beneath the Hengyang-Kunming Highway in China. Three-dimensional numerical analysis was performed to investigate the mechanical performance of the pipe roof, and the stresses of the pipes were measured in the field using a series of strain gauges. Reasonable agreement was found between the observed field measurements and the numerical results. Such results indicate that the stress distribution of the pipe roof can be divided into three sections: a tension section right near the entrance casing arch, a compressive section behind the tunnel face, and a tension section ahead of the tunnel face. The peak stress values take place approximately at the middle of each section, which varies with the advancement of the tunnel face. This analysis provides a reference for evaluating the mechanical response of the long and large pipe roof in reinforcing shallow tunnel passing below highways.

In general, a concrete slab of a concrete-faced rockfill dam (CFRD) is viewed as a macroscopically uniform but microscopically nonuniform material. Study of the damage process of high CFRD subjected to strong motion is crucial for evaluating its safety during an earthquake. Therefore, dynamic analysis with consideration of the nonuniformity of the concrete should reveal the damage mechanism and provide suggestions for engineering design. In this paper, the elastic–brittle damage model proposed by others and applied to the failure simulation of rock and concrete under static loading was developed for this purpose. The impact of the randomness of the modulus of elasticity and tensile strength of concrete on the distribution characteristics of mechanical damage of the face slab of the rockfill dam was studied. The study considered the randomness of the distribution of material parameters combined with principles of statistics, analyzed using two-dimensional finite-element numerical analysis. The results of the calculation indicate that when the randomness of material parameters of the concrete slab was not considered, the stress of the face slab along the slope direction was larger at ∼0.65–0.85H (H is the dam height) and the tensile damage occurred mainly near 0.8H. As the nonuniformity of the concrete material increased, the location in which tensile damage occurred tended to vary but was concentrated mainly in the ∼0.4–0.9H region of the slab. As a consequence, this part of the face slab is the seismic design focus region. Through the use of elastic–brittle micromechanical damage models and by considering the material parameter randomness, the seismic damage process, damage distribution, and typical damage modes can be intuitively illustrated, which makes it easier to understand the weak points of the slab. The results of this study can provide a reference for the seismic design of CFRD.

This study investigated the structural response of segmental tunnel linings to tunnel-boring machine (TBM) advance during the construction of a typical tunnel built in Mexico. Because of the thrusting of the TBM during excavation, an axial load acts along the longitudinal axis of the tunnel. This axial load decreases as the TBM advances away from the tunnel lining. However, the residual axial load continues acting on the lining, producing a coupling between rings that affects the structural response of the tunnel. In this paper, this effect is studied by means of finite-element models. A nonlinear parametric study was carried out in which the material properties, the influence of the number of rings, the residual axial load, and the position of continuous joints were examined. The numerical models were calibrated with (lab-based) experimental results obtained from the literature on a typical tunnel built in Europe. It was concluded that the residual load increases the structural capacity of the lining. Also, the study showed that the collapse mechanism was modified by the coupling between rings. Rings will fail by excessive deformations with less coupling, while with greater coupling, the collapse mechanism is caused mainly by cracking in the segments. Therefore, it is necessary to consider the effect of the TBM advance to evaluate the structural response of a segmental tunnel better.

Continuum upper-bound limit analyses in existing literature are based on empirical formulas or singular analytical solutions for a uniform-convergence type of tunnel boundary condition. This paper presents an upper-bound limit analysis of shield tunnel stability in undrained clays using complex variable displacement fields for four different ground-loss scenarios. The upper-bound theorem was applied on a prescribed perfect plastic Tresca kinematic zone with a slip line boundary to seek the supremum (minimal upper bound) of the tunnel stability number, which should not be exceeded to avoid collapse. For an imposed identical volume of ground loss, the maximum ground surface settlement was found to be the smallest for ground-loss Scenario A (circular convergence), larger for Scenario B (downward oval convergence), and much larger for Scenario C (halved oval convergence), which is slightly smaller than Scenario D (mixed oval convergence); the opposite is true for comparisons of the widths of the settlement troughs. Ground-loss Scenario A presents the worst case in terms of tunnel stability, with the smallest allowable stability number and the widest spread of the least favorable slip line boundary, while Scenario D is the second worst case with the second-smallest allowable stability number. Similar results were found, in sequential order, for Scenarios B and C. The presented approach, because of the complex variable solutions used, may extend upper-bound limit analyses to more complicated tunnel boundary conditions.

In this study, rockbolts made of polypropylene random copolymer (PP-R) material, instead of the steel split sets, were assessed with a series of experimental studies including both laboratory- and field-scale tests. PP-R tubes and typical steel split sets were comparatively investigated by performing static loading (pull and shear), impact loading, corrosion, diametric compression, insertion into drill holes, and creep tests. PP-R tubes with good chemical resistivity and mechanical properties that are economically used in drinking water and pressurized gas transportation were assessed to be usable as frictional rockbolts in rock engineering. Despite the advantages of being a noncorrosive material, being shaped by the roughness of drill hole surfaces, and having ideal support reactions because of high crack propagation resistivity, strain relaxation was found to be considerable for the PP-R tubes inserted into the drill holes. Results obtained from this study suggest developing new bolts when using PP-R tubes instead of using the steel split sets.

Drained triaxial tests were performed to investigate the loading-creep coupling effect in a rockfill material using a modified triaxial apparatus. The modified apparatus can switch between stress-controlled and strain-controlled modes; thus, it enabled long-term multistage loading and creep. The test program was carefully designed to study two main concerns: (1) influence of creep on deforming characteristics under postcreep loading and (2) influence of loading history on creep characteristics. A strong coupling effect between loading and creep was observed in the tests. It was found that creeps change the deforming characteristics in the postcreep-loading stages through strain hardening, and the creep was influenced not only by the stress state but also by the precreep-loading pattern. The creeps after elastic and elastoplastic loadings showed different behaviors. It was further shown that the loading-creep coupling effect can be interpreted using the hardening plasticity theory.

The two-dimensional (2D) dynamic response of horizontally aligned, cylindrical twin tunnels subjected to vertically incident seismic waves was simulated by a finite/infinite element approach. A rational approach was proposed for imposing the earthquake forces using free-field recorded data. First, the earthquake motion recorded on the free field was transferred to that on the boundary of the near field using the one-dimensional (1D) wave theory. Second, the motion data were computed as the equivalent seismic forces and applied on the near-field boundary in the frequency domain. In this study, the data from the 1999 Chi-Chi earthquake recorded at the TAP003 station were adopted. The accuracy of the procedure for imposing the free-field earthquakes was first verified. Then, a parametric study was performed to investigate the effects of spacing between the twin tunnels, depths of tunnels, and stiffness of tunnel lining under seismic excitation. The results of the analysis indicate that although the depth and spacing of the twin tunnels have less effect on ground response, they are important parameters for the seismic responses of the tunnels.

This paper presents the results of a series of numerical experiments using a grain-based discrete-element model approach to investigate the effects of cementation on the mechanical behavior of a low-porosity brittle rock. The adopted approach enables the incorporation of multigrains for a given composition and explicit simulation of intergranular and intragranular cracking, which are important features in the simulation of brittle rocks. The results show that cementation has significant effects on the macroscopic behavior of brittle rock in many aspects, including crack-initiation and crack-damage thresholds, stiffness, peak strength, brittleness, and failure patterns. In general, as bond strength increases, the secant Young’s modulus, the peak strength, the ratio of crack-initiation threshold to peak strength, and the ratio of crack-damage threshold to peak strength decrease. The lower the bond strength, the earlier the volumetric strain reversal occurs and the earlier the absolute dilation occurs. It is observed that the model with the higher bond strength appears to be more brittle. The significance of those effects is found to decrease as confining pressure increases. The proposed approach provides a very useful tool for simulating granular materials at a microscopic level.

In the past 15 years, different researches have shown that the effective-stress approach represents a simple and precise way to generate fully coupled constitutive models for unsaturated soils. This is so because the influence of the degree of saturation and the hysteresis of the retention curve are implicit in the formulation. Here, an elastoplastic framework for the volumetric behavior of expansive soils based on effective stresses is proposed. The hydraulic behavior of the soil is simulated using a porous-solid model able to reproduce wetting–drying cycles. The porous-solid model is based on the current pore-size distribution (PSD) of the soil. Therefore, volumetric deformations can be related to variations in the PSD. The result is a fully coupled elastoplastic framework based on the equation of the volumetric behavior of saturated soils where the compression index depends on the position and direction of the state of stresses with respect to the yield surfaces. Experimental and numerical comparisons show the ability of the model to simulate the behavior of expansive soils under different stress paths.

This paper presents a simple proof of an initially counterintuitive result that the interparticle effective forces in a particulate aggregate can be meaningfully represented using an infinite number of uniaxial stress tensors. The result is shown to be consistent with previous work in particle mechanics. It does not imply that constitutive behaviors are combinations of uniaxial behaviors. A further level of sophisticated continuum approximation is also identified. Some implications for constitutive modeling are discussed.

It has long been discussed whether Terzaghi’s expression for effective stress holds true for all saturated soils. To examine the physical basis of the effective stress expression, a new mechanical model is proposed. According to that model, the fraction of pore pressure depends on the porosity and the proportion of the particle surfaces to which the pore pressure is applied. The new expression is then tested against the experimental evidence for varied soils. For cohesionless soils, values of $\eta$ (the faction of pore pressure) are close to unity, because the real contact area is extremely small. Significant deviation from Terzaghi’s expression occurs only at very high stresses. For cohesive soils, a method is developed to calculate the $\eta$ values based on the data from shear strength tests. A variation of factor $\eta$ with effective stress is obtained for five different clays. Significant reduction in $\eta$ is observed for clays with a high plastic limit. Without consideration of this reduction, effective strength parameters may be overestimated for the consolidated undrained triaxial tests.

This paper presents an analytical solution for the consolidation behavior of deep cement mixed (DCM) column–improved ground on the basis of the equal strain condition. The proposed analytical solution accounted for the vertical permeability and rigidity of DCM columns and natural soil, stress transfer, and radial drainage. The solution was based on the theory of one-dimensional consolidation along with the equivalent vertical permeability and coefficient of consolidation. The analytical solution was first derived assuming equal permeability in both DCM columns and surrounding soil and then modified to include the radial drainage effects for the case with different permeabilities in DCM columns and natural soil. The performance of the proposed analytical solution was compared with the numerical simulations on the basis of FEM and an analytical solution found in the literature for the DCM column–improved ground. The proposed analytical model was also verified using physical model test results found in the literature for DCM column–improved soft Bangkok clay. The composite coefficient of consolidation of DCM column–improved ground can be predicted within approximately 5% error using the present analytical model.

The lateral soil resistance available to pipelines partially embedded in a seafloor is of interest in evaluating pipeline lateral buckling capacity, stability under forces resulting from current loads, or route pullout loads. An upper-bound limit analysis method, including equilibrium requirements in a manner common to lower-bound theories, was used to evaluate lateral soil resistance to pipe displacements. The method is applicable to sand and clay foundations with homogeneous or layered conditions. Comparisons with results from physical tests and other limit analysis and finite-element investigations are presented. The numerical limit analysis procedure was implemented through numerical-computing software. An optimization procedure was used to identify the minimum resistance satisfying the governing objective equations. The seafloor surface geometry may include soil berms or other features. The soil strength may be described by a linear Mohr-Coulomb criterion or a curved criterion representing a varying material friction angle.

This study undertook stability analysis of nailed soil slopes using the limit-equilibrium method (LEM) and considering a three-dimensional (3D) rigid-body rotational failure mechanism with the assumed slip surface being a part of a sphere. The moment equilibrium of the 3D wedge formed by the slope surface and the slip surface along with the nails embedded in it were analyzed as a whole. A specific-purpose computer code was written for factor-of-safety (FS) computation; the developed computer code is capable of analyzing an unreinforced slope and a nailed slope. The critical slip surface and the corresponding minimum FS value of the unreinforced slope were initially determined, taking into account all possibilities of failure (base failure, slope failure, and toe failure). For the critical slip surface so obtained, nails were then introduced at desired positions, and the FS value for the nailed slope was then estimated with the developed procedure. The developed method and computer code were verified by comparing the FS values of some benchmark problems [two-dimensional (2D) and 3D] obtained by the proposed method with those reported in the literature. The critical slip surfaces obtained from the proposed method were also compared with some of the benchmark problems. A parametric study was conducted to determine the effects of the inclination and spacing of the nails on the FS values.

Seismic responses of various buildings are calculated by a three-dimensional (3D) linear method for examining the soil-building interaction based on an input seismic wave field in the reclaimed zone of Tokyo Bay in which ground motions include a considerable amount of surface waves. A seismic wave field means seismic waves propagate in a 3D medium. The method was recently proposed to adequately treat surface waves trapped by a deep (several kilometers) underground structure in a soil-building interaction system. First, seismic responses of a building were calculated at two soft-soil sites for three large earthquakes to understand the variations in building responses with reference to sites and earthquakes. Second, seismic responses of low- to high-rise reinforced concrete (RC) and steel buildings and wood buildings were compared at a soft-soil site for a large earthquake, evaluating the relative seismic risk of various buildings. Midrise RC and steel buildings shook more severely than low-rise and high-rise RC and steel buildings. Flexible wood buildings suffered extremely large interstory drifts, indicating the largest seismic risk.

In the present study, the bearing capacity of rectangular footings resting on multilayer geosynthetic-reinforced granular fill overlying soft soil is investigated. Five different sizes of model footings are chosen in such a way that the aspect ratio of the footings is varied as 1.0 (square), 1.5 (rectangular), and 2.0 (rectangular). The effectiveness of multilayer reinforcement is assessed by comparing the bearing capacity improvement factor, settlement reduction factor, and load-spread angle. The variations of these factors with the aspect ratio of the footings are also studied. The optimum value of the thickness of granular fill over soft soil and sizes of the reinforcement as obtained for single-layer reinforcement placed at the granular fill-clay interface are selected for the entire test program. In some of the model tests, the reinforcement layers are instrumented with strain gauges to study the strain distribution along the reinforcement layers. The test results show that the improvement factor and settlement reduction increase with a decrease in the aspect ratio of the footing, and the increment is more for the multilayer-reinforced case (N > 1). However, the increment is more for the constant width case than with the constant length case of the footing. The load-spread angle increases with an increase of the L/B ratio of the rectangular footings, and the rate of increment decreases due to an increase in the number of reinforcement. An analytical solution is also proposed to estimate the ultimate bearing capacity of rectangular footings with various aspect ratios resting on the multilayer geosynthetic-reinforced granular fill of limited thickness underlain by soft soil. The predictions of the bearing capacity made by the developed model are found to be in good agreement with the experimental results.

The discrete-element method (DEM) has been successfully used to simulate the behavior of granular material and was used in this study to analyze the stresses and deformations of a single geogrid-encased stone column under unconfined compression. The aggregate was simulated using graded particles of diameters ranging from 30 to 50 mm, and a biaxial geogrid as an encasement material was simulated using parallel-bonded particles. The micromechanical properties of the aggregate were determined using numerical triaxial tests at various confining stresses. The tensile properties of the geogrid were determined by a multirib tensile test, and the flexural rigidity of the geogrid was calibrated by a flexural bending test. This study investigated the changes in vertical and radial stresses and porosities, the contact-force distribution and particle movements within the aggregate, and the deformation and tensile force in the geogrid encasement. The load-displacement response of the DEM model of the geogrid-encased aggregate sample closely agreed with the experimental results. The coefficient of radial stress, defined as the ratio of vertical stress to radial stress within the aggregate, varied from 0.6 to 2.7 during loading where the tensile strength of the geogrid encasement was not fully mobilized. The aggregate showed volumetric contraction at small deformation and then dilation with an increase of deformation. The interlocking effects between the aggregate and the geogrid were observed at the initial state. The particles within the middle portion of the column were more likely to slip than those at other locations.

Cracking has a significant impact on dam safety. A discontinuous hybrid finite-element meshfree (FE-meshfree) method, which inherits advantages from both the FEM and the meshfree method, was developed to investigate the mechanism of cracking in concrete dams. In this paper, first, the performance of the hybrid FE-meshfree method was validated by comparing it to existing experimental and numerical results of a scaled physical dam model without hydraulic pressure. Then, the mechanism of single- and multiple-crack propagations with hydraulic pressure was investigated numerically. It was found that all cracks propagate toward the toes of the structures in the downstream side. The influence of hydraulic pressure seems to become weaker from the top to the bottom of a dam.

This paper presents an investigation of wave propagation through microfractured rock mass. The effects of microfracture on wave propagation were observed by a series of scanning electron microscope (SEM) tests and wave-velocity measurements. A spectrum analysis was introduced to analyze the attenuation coefficient and the wave number of seismic waves propagating through microfractured rock mass. The effects of fracture length, fracture quantity, and frequency of incident wave on the attenuation rate, effective velocity, attenuation coefficient, and wave number were numerically simulated and discussed. The results demonstrate that the attenuation rate, effective velocity, attenuation coefficient, and wave number are significantly influenced by the geometrical parameters of microfracture (e.g., length and quantity). In addition, the numerical manifold method (NMM) was validated as a method for investigating the dynamic behavior of heavy microfractured rock mass efficiently.

This paper presents a methodology for predicting the mobilized response of axially loaded piles in sands in the states of pre-liquefaction and post-liquefaction. The proposed procedure calculates shaft and skin resistance of axially loaded piles in sands with and without liquefaction. Sands with limited liquefaction (mostly medium-dense sands), in which the shear strength of the sand drops under a cyclic loading (seismic events), were the focus of this study. The proposed approach provides the load transfer-settlement (t-z) curve and the pile-head axial-load versus pile settlement in sands before and after the development of soil liquefaction. It also considers the variation of pore-water pressure (PWP) in the near-field soil caused by axial loading combined with free-field PWP that is generated by cyclic loading as a postseismic event. The mobilized pile skin and tip resistances were determined on the basis of two constitutive models (of stress–strain relationship) for sands under drained and undrained conditions. A computer code was developed to implement the presented technique.

Heavy-haul railway embankments in China are generally constructed with coarse-grained granular (CGS) materials. The accumulation of permanent deformations in CGS materials remains a significant concern and technical challenge because the CGS layer sustains a considerable portion of the intense train-loading transferred from overlying structures. Previous research studies demonstrated that the critical cyclic stress (CCS) level significantly affects the accumulative permanent (or plastic) deformation. This paper presents the results from a series of repeated-load, undrained, permanent deformation triaxial tests conducted in the laboratory using a customized large-scale triaxial apparatus. CGS specimens prepared with different moisture contents were subjected to different combinations of confining and deviator stress levels. The accumulation of permanent axial strain as a function of the number of load cycles was recorded for each specimen during the tests. The influences of moisture content, confining pressure, and deviator stress on modulus and permanent axial strain accumulation characteristics were analyzed. Empirical formulas for calculating the elastic modulus and accumulated permanent axial strain are proposed. The findings in this study could provide guidance for designing similar heavy-haul railway embankments.

A Timoshenko beam-on-Pasternak foundation (T-P) model was developed to estimate the horizontal dynamic impedance and interaction factors for inclined piles subjected to horizontal harmonic load. The inclined pile with a fixed pile-to-cap connection was modeled as Timoshenko beams embedded in the homogeneous Pasternak foundation. The reactions of the soil on the pile tip were simulated by three springs in parallel with corresponding dashpots. The differential equations of normal and axial vibrations of the inclined pile were solved by means of the initial parameter method. The model and the theoretical derivations were validated through comparisons with results from other theoretical models for some large-diameter end-bearing piles and inclined piles. The effects of shear deformations of the soil and inclined piles, during the vibration, were highlighted by comparing the results of the T-P model with those from Euler beam-on-dynamic-Winkler foundation (E-W) model. Findings indicated that the T-P model is more accurate than the E-W model for analyzing the dynamic performance of the inclined piles with small slenderness ratios and large inclined angles. The effects of the inclined angle, slenderness ratio, and distance-diameter ratio on the dynamic impedance and interaction factors were studied by numerical examples. It is shown that the increased angle of the pile results in an increase of horizontal impedance and decreases in interaction factors.

Response of geothermal energy piles in sand under combined thermal and mechanical loading was investigated in the present work using a nonlinear axisymmetric finite-element (FE) analysis procedure. In this study, the piles were considered to behave linear-elastically. The stress-strain behavior of sand was simulated using a state parameter–based constitutive clay-and-sand model (CASM), which was implemented in FE software through a user material subroutine. The geothermal energy piles of different lengths and diameters with floating and end-bearing conditions in sand were analyzed under mechanical and thermomechanical loading to study the displacements of soil and pile through axial and radial strains in the pile and axial stress in the pile. In addition, parametric sensitivity studies were carried out by varying the relative density of sand and thermal load on the pile. Results showed that the relative density of the sand, applied thermal load on the pile, and the end condition of the pile govern the relative displacement between pile and soil. Also, axial stresses under thermomechanical loading were greater than they were under only mechanical loading.

This paper examines the potential influence of particle-size distribution on stress-dilatancy behavior of granular materials from the results of 35 conventional drained triaxial compression tests. Seven different grain-size distribution curves of two different materials (glass beads and Péribonka sand) in the range of 63–2,000 µm were tested at different normal pressures and initial relative densities. It was shown that for a given relative density and confining pressure, although shear strength and volumetric response of the tested materials were independent of the coefficient of uniformity, $C_u$, in the investigated range, they were significantly influenced by the variation of the mean particle size, $D_{50}$. On the basis of the triaxial test results, a correlation between the material constant $\alpha$ of a modified stress-dilatancy equation and D₅₀ of the tested materials was found. In addition, the coefficient of an equation, which was introduced as an experimental adjustment of the well-known stress-dilatancy equation, were fine-tuned to account for $D_{50}$. A comparison of the predictions by the proposed empirical formulas with stress-dilatancy data from the literature and a micromechanical explanation of the experimental results are also provided.

This paper presents and discusses the results of a three-dimensional numerical study performed to evaluate the effects of vertical loads on the response of laterally loaded piles in both homogeneous and layered soils. Piles were treated as linear elastic materials, whereas soils were idealized using the Mohr-Coulomb constitutive model with a nonassociated flow rule. Vertical loads, corresponding to several percentages of the ultimate pile load, were imposed prior to the application of lateral loads. In a homogeneous sandy soil, numerical results showed that the lateral resistance of the pile did not vary considerably with vertical loads. However, the presence of vertical loads on a pile embedded in clayey soil was found to be detrimental to its lateral capacity, and it is unconservative to design piles in clays assuming there is no interaction between vertical and lateral loads. In layered soil media, which is the main part of the current study, it was found that the effect of vertical loads depends on not only the characteristics of soil surrounding the piles but also those located beneath their tips.

Natural loess with large voids and weakly bonded structures is widespread in the arid areas of the world, particularly northwestern China. Recent experimental studies have shown that the mechanical behavior of natural loess is stress path dependent. In practice, soils influenced by the construction of earthen structures may undergo various complex stress paths that are very different from the conventional stress paths commonly considered in geolaboratory experiments. Because of the limitations of current technologies, real stress paths are difficult to obtain from field tests or physical modeling. This study focused on the deformation behavior of natural loess from Jingyang, China, under the stress paths around a shield tunnel. First, the stress paths around a shield tunnel were determined from the numerical data obtained at different positions in a distinct-element simulation of shield tunnel excavation in sand (for simplicity) and by using a novel method referred to as the equivalent stress ratio method. Second, a set of undrained triaxial tests were conducted using the conventional and complex stress paths. The experimental results demonstrate that the deformation characteristics of the loess are different at different positions around the shield tunnel, and the largest deformation appears in the lateral zone (0°). This indicates that the lateral zone is the key zone to be controlled during shield tunneling. In addition, the relationship between the stress increments and the strain increments varies with the stress path. In a complete unloading path, the behavior of natural loess is largely elastic and linear. On the contrary, in a complete loading path or semiloading path, the behavior is largely inelastic and nonlinear, and this behavior is associated with the stress state and recent stress history. These results are valuable in establishing the constitutive relationships for natural loess under complex stress paths and may be useful for the construction of shield tunnels in loess areas.

This study presents a closed-form solution for kinematic stability of a two-stage slope with a strip footing placed near the slope crest of the layered soil strata. According to the upper-bound theorem of plasticity theory, the normalized ultimate bearing capacity and yield seismic coefficient that the slope could withstand without failure under the limit state are derived on the basis of the pseudostatic approach. In addition, under specific parameters, the least upper-bound solutions can be calculated with the use of optimization. The stability factors were compared with those in existing literature under static, seismic, and undrained conditions to validate the proposed approach and the analytical solutions. A thorough parametric study involving parameters, such as soil cohesion and self-weight, nonhomogeneous coefficients, and external conditions (including the magnitude and position of strip footing and seismic effect), was carried out in this study. The findings obtained, considering a log-spiral failure mechanism under drained conditions and a circular mechanism for undrained conditions, could provide useful reference for the preliminary design of a two-stage layered slope.

Given the three-dimensional confinement, the geocell reinforcement can act as a beam that can carry both bending and membrane stresses compared with only the planar membrane effect of planar reinforcement. This study presents an analytical approach to determine the factor of safety (FOS) of geocell-reinforced slope using the horizontal slice method (HSM). The geocell reinforcement composed of geocell and infill soil was modeled as a composite beam filled with soil. The improvement in the FOS of the geocell-reinforced slope was expressed in terms of vertical stress dispersion, vertical frictional resistance, and structural mechanisms provided by geocell reinforcement. The effect of geocell pocket diameter on the soil confinement and FOS of geocell-reinforced slope was considered using hoop tension theory. The results of the proposed analytical model were compared with those determined by numerical modeling using the strength reduction method (SRM). A series of parametric analyses were also performed to evaluate the influence of the placement depth of the geocell layer, the number of geocell layers, the pocket diameter and the height of geocell, and the slope angle and soil shear strength, on the stability of the geocell-reinforced slope. The results indicate that the reinforcing mechanism of geocell reinforcement is considerably related to the geocell thickness. The mobilized flexural strength and vertical frictional resistance magnify as the height of the geocell increases. Compared with planar reinforcement, a smaller quantity of geocell reinforcement is required to achieve an equivalent FOS value. The results predicted from the present analytical approach were found to be in good agreement with SRM results.

The rock mass surrounding a subsea tunnel often contains seawater, and the coupled effects of an earthquake and seepage introduce more uncertainty into analyses of tunnel safety. However, research on this topic is still lacking. In the present study, models of structure and fluid fields were established by considering the effect of a two-dimensional viscoelastic boundary condition, and the stability of a cross-sea tunnel structure under seepage and a bidirectional earthquake was studied. Using a static strength-reduction method on the basis of dynamic finite elements, a stability-safety coefficient was obtained. In addition, the influences of sea depth, overlying rock thickness, and permeability coefficient on the seismic dynamic stability-safety coefficient and varying characteristics of the plastic zone in a cross-sea tunnel structure under seepage and a bidirectional earthquake were studied through numerical examples. The results showed that under this type of earthquake, plastic zones first appeared on both sides of the tunnel arch feet and in the peripheral areas of the arch shoulders; by contrast, the vault was secure, and no plastic zone appeared in this area. When all factors were considered, the plastic zones extended farther when the overlying rock thickness and sea depth were greater. When the overlying rock was thick and the rock mass surrounding the tunnel was only slightly weathered, the rock mass was close to intact, and as a consequence, the permeability coefficient did not significantly affect the development of the plastic zone or the stability-safety factor. The influences of these three parameters on the safety of a subsea tunnel, as obtained in this paper, can provide a theoretical basis for the reasonable design of submarine tunnels.

An exact approach is used to discuss the Love wave behavior in a composite reinforced structure. In this body, the reinforced medium is covered by an initially stressed isotropically half-space from above and an initially stressed orthotropically half-space from below. The generalized dispersion relation of the Love wave is obtained in the presence of associated initial stress and reinforced parameters, which approve the significant effect of these parameters on the propagation of the Love wave in a composite fiber-reinforced structure. The obtained dispersion equation is in closed form, which is in agreement with the classical Love wave equation. Moreover, some important peculiarities are observed in the graphs.

The reinforced piled embankment has been widely used in highway and high-speed railway because it is effective in reducing total and differential settlement. This paper presents an analytical solution for estimating the settlement of pile and soil and the distribution of skin friction and the neutral plane of the pile in the reinforced piled embankment over elastoplastic consolidated soil. The soft soils were assumed to be elastic-plastic materials with settlement calculations as determined by one-dimensional nonlinear consolidation theory. The load-transfer mechanisms accounting for soil arching and tensioned-membrane effects on the reinforcement and pile–soil interaction (skin friction along the pile), considering soil consolidation, were comprehensively investigated. The analytical solution was validated by three case studies and was shown to be a reliable method with acceptable accuracy with predictions overestimating the measurement by approximately 10%. The maximum settlement of soil was found to increase with increasing pile spacing while the soil constrained modulus decreased. The soil constrained modulus was a much more sensitive factor of influence on the maximum settlement of the soil than was the pile spacing.

This paper reports on a new framework for interpreting cone penetrometer data in stiff-soft-stiff deposits, with the aim at identifying layer boundaries and interpreting accurately the undrained shear strength for each layer. An extensive parametric study was conducted using large deformation finite-element (LDFE) analyses. The LDFE results were used to establish the interpretation framework. Regardless of the strength and the rigidity index ratio between two successive layers, where the cone penetrates from stiff to soft clay layers and the reverse, the layer interface can be demarked at 1.3 D (D is the cone diameter) above and 0.8 D below the gradient discontinuity on the penetration resistance profile in the soft layer. The undrained shear strengths of the first and third (stiff) layers can be interpreted using a single-layer approach and the resistance profile without the influence of the adjacent soft layer. The interpretation for the interbedded second layer necessitates implementing a correction factor, which is shown to be a function of the relative thicknesses of the first and second layers, and the rigidity indexes and strength ratios of the adjacent layers. By combining the findings with the results from a previous study on an interbedded stiff clay layer, a complete design chart is proposed for a thin soft or stiff layer embedded in a thick clay layer. The proposed design framework is illustrated by a flowchart for practical use.

The method of fragments can be used to efficiently obtain solutions to a variety of two-dimensional seepage problems, especially confined flow problems. With this method, the flow domain is divided into fragments that span zones, which are defined between certain critical planes, based on the assumption that the equipotential lines through each such plane are coincident with the plane(s) in question. A dimensionless form factor is then defined for each fragment, and the total flow rate is computed using these form factors in a straightforward manner. An extension of the method of fragments to the axisymmetric cofferdam problem is presented in this paper. A range of numerical simulations was used to generate design charts to obtain the required axisymmetric form factors and exit gradients. These were validated against detailed numerical solutions and against analytical solutions reported in the literature. The design charts presented in this paper are considered to provide very reliable estimates of the seepage conditions and for a wide range of cofferdam geometries of practical interest.

In the stability analyses of a reinforced slope with a grid beam anchored by cables, the anchoring force of the cable is usually simplified as the concentrated force acting on the slip surface to calculate the reinforcement effect. The anchoring force actually acts on the slope surface as stress because of the effect of the grid beam. Therefore, this work proposes two new calculation modes of anchoring force: stresses with rectangular and curved distribution acting on the slope surface. In addition, the analysis considered the presence of a cavity, which results in a void underneath the grid beam near the slope surface. Then, two types of slip surfaces and the Morgenstern-Price method were adopted to study slope stability. Thus, the following conclusions were obtained: (1) three calculation modes have nearly similar solutions with less than 5% difference; (2) the arbitrary curved slip surface is suggested to be used as the critical slip surface that shows a noncircular shape; and (3) the void causes anchorage cable failure, which reduces slope stability significantly.

In this study, three-dimensional finite-element models incorporating a Mohr-Coulomb elastoplastic material model were validated for the evaluation of the shape effect of square and circular surface footings under vertical loading in $c$-$\varphi$ soil. The numerical models were found to closely predict experimental load-settlement relationships. The shape effect was also investigated in relation to the progressive failure around the foundations and the shape of the failure mechanism inside the soil. With detailed parametric studies, the shape factors of square and circular surface footings can be fitted by simple functions of the soil friction angle and footing embedment depth.

The strength envelopes of almost all types of rocks are nonlinear over a wide range of normal stresses. This paper presents a study in which the nonlinear Hoek-Brown failure criterion was adopted and the kinematical approach of limit analysis was used to compute the three-dimensional (3D) stability of rock slope subjected to pore-water pressure. A generalized tangential technique was used to formulate a 3D stability problem as a classical optimization problem. The objective function, to be minimized with respect to the locations of the sliding body and tangency point, corresponded to dissipated energy. The pore-water pressure was incorporated into the objective function, and the effect of it on 3D stability is discussed. The numerical results for different types of rocks are presented for practical use.

This paper investigates the ultimate bearing capacity factor (N_γ) and failure mechanisms of multiple rough strip footings with equally clear spacing (S) placed on pure sand using the upper-bound finite-element method with rigid translatory moving elements (UBFEM-RTME). Parametric analysis is performed by varying the dimensionless clear spacing (S/b) and the sand friction angle (ϕ), and all footings are assumed to be loaded to failure simultaneously with identical bearing loads. The critical spacing distance (S_cr/b) and N_γ increase continuously with the increase in ϕ. With the S/b decreasing from S_cr/b, the N_γ values are found to increase slightly before a rapid increase. The obtained failure mechanisms are primarily composed of mesh-like rigid blocks and a completely curved trapped wedge below the footing base. The relative movement of blocks around footing edges becomes particularly intensive, especially for closely spaced footings and sand with high values of ϕ.