International Journal of Geomechanics

Pile foundations may lose their lateral resistance in earthquake-induced liquefaction and may fail not only by bending and shear forces but also buckling. Although research has been done on the buckling of pile foundations, it is still necessary to investigate further the buckling of pile foundations during an earthquake and a corresponding efficient countermeasure. Some existing pile foundations may not meet the requirement of present seismic design standards and are vulnerable to buckling failure. In the present study, numerical analyses and model tests were conducted. The validity of the proposed numerical method was first verified through a 1-g shaking table test. Then, the buckling risk of a group-pile foundation and its strengthening with partial ground improvement (PGI) were carefully estimated. Meanwhile, the effectiveness of the proposed countermeasure with PGI against the buckling of the group-pile foundation was confirmed by a static model test. The purpose of the study was to investigate the effectiveness of ground improvement for the retrofitting of vulnerable pile foundations against buckling due to seismic loading.

Laboratory model tests were conducted on an aluminum model pile embedded on a crest of soft clay. The slope angle and L/D ratio (L = embedded length, D = diameter of pile) were varied, and the pile was subjected to lateral loads at the pile head by a loading frame and frictionless pulley arrangements. Through the experimental investigation, the effect of the L/D ratio and slope on the behavior of the pile was studied. To incorporate the effect of slopes and L/D ratios, an empirical equation was also developed with the use of multiple regression analysis. It was observed that as the ground slope changed from level to a 1V:5H slope (11.30˚), the influence of the slope on pile capacity became negligible.

In order to investigate the impact of fault on the stability of the water-resisting layer of the coal floor, the critical water pressure formula of the water-resisting layer failure under the influence of fault is deduced respectively by using brittle fracture criterion in fracture mechanics and the shear failure limit equilibrium condition in rock mechanics. The corresponding mechanics criterion of water inrush from the coal floor is proposed. Then the critical water pressure affected by the width of the coal pillar, the thickness of water-resisting layer, the dip angle, and mechanical property of fault is analyzed and discussed. Finally, the validity of the proposed mechanics criterion of water inrush is verified by the example analysis of coal mine engineering. The results show that (1) the smaller the dip angle of fault, the less the critical the water pressure, and the floor is more prone to water inrush; (2) the critical water pressure is positively correlated to the cohesion of fault. The smaller the cohesion of fault, the greater the possibility of water inrush; (3) the bigger the coal pillar width, the larger the critical water pressure, and the floor is less prone to water inrush; and (4) the critical water pressure linearly increases with the thickness of the water-resisting layer. The larger the thickness of the water-resisting layer, the smaller the possibility of water inrush.

Failure surfaces are very effective in active lateral earth thrusts acting on cantilever retaining walls. The intersection of failure surface and cantilever retaining wall should be taken into account for determination of active earth thrust. Calculations of lateral earth thrusts vary for two different cases, short heel or long heel, based on the intersection of cantilever wall and failure surface. However, the common methods are devoted to a particular case (long heel or short heel). This study intended to suggest a new lateral earth thrust method that is applicable to cantilever walls with a short heel or long heel using the limit-equilibrium approach. For this purpose, an earth thrust-maximization algorithm was prepared and coded by using Matlab Environment to determine active earth thrust coefficients and failure surface inclination angles occurring behind a cantilever wall in an active case. Also, the failure surfaces occurring behind model cantilever walls and the failure cases were examined experimentally by using particle image velocimetry (PIV) analysis. Consequently, long-heel and short-heel cases and the effective parameters on the cases were investigated analytically and experimentally.

The shear stress–displacement behavior and shear-strength parameters of the interface between the cement grout nail and surrounding soil are important factors in the design and safety assessment of a soil-nailing system. One of the most commonly used methods to measure the interface shear strength of a soil-grouting system is the direct shear testing method. This study aimed to investigate the behavior of the interface between the cement-grouted materials (soil nails) and sandy soil using direct shear test apparatus, make a comparison between the sand–sand interface and grout–sand interface, and calibrate an interface model to be used in simulations of soil-nailing systems. The effect of the water:cement ratio of the grout and the relative density of the sand on the interface behavior is also investigated. The findings show that, in general, the behavior of interfaces is similar to that of dense sand in terms of strain softening, and their peak and residual friction angles were found to be approximately 8 and 4% higher, respectively. The setting time of the grout and relative density of the sand were not found to affect friction angles significantly, whereas cohesion intercepts were affected by it. Finally, the model calibrated herein was found to have good agreement with experimental data and could be used for soil-nailing simulations.

Parallel joints are ubiquitous in geological rock mass and seriously affect rock excavation in underground mining and civil engineering. In this study, the propagation characteristics of shock waves subjected to blasting load in a parallel jointed rock mass were investigated using field testing and three-dimensional finite-element numerical modeling. The method of instantaneous energy was first adopted to mine the recorded information about the interaction between joint planes and shock waves; then, the displacement discontinuity method (DDM) was used for the characterization of joint surfaces in the numerical model. The effects of joint mechanical properties, including joint spacing and joint normal stiffness, were also evaluated. The results showed that the instantaneous energy provided a powerful tool for reflecting the localized singularity of energy due to the wave reflection and superposition caused by joint planes. It is clear that the wave reflection in the component perpendicular to the joints was significant with a prolonged action time. Compared with the intact rock mass, the amplitude of shock waves in the jointed rock mass was increased by 2–3 times with highly complicated attenuation, and stress waves were divided into a series of equivalent new sources by the joints in the direction perpendicular to parallel joints. It was also found that the joint properties had a great effect on the propagation of blast-induced vibration.

On the basis of a systematic parametric study, three-dimensional (3D) finite-element (FE) simulations were conducted to evaluate mitigation by the stone column (SC) approach. Mildly sloping saturated cohesionless strata (uniform as well as stratified) were investigated under the action of an applied earthquake excitation. For that purpose, the open-source computational platform OpenSees was employed, through a robust user interface that simplifies the effort-intensive pre- and postprocessing phases. Specifically, a number of SC configurations (1 × 1, 2 × 2, and 4 × 4) for a given area replacement ratio (A_rr) were explored. In these configurations, the same A_rr was maintained by deploying smaller-diameter columns, evenly distributed spatially so as to increasingly reduce the drainage path. As such, it was found that a more evenly distributed SC configuration (e.g., the 2 × 2 configuration compared to the 1 × 1), with a shorter drainage path, is more effective in decreasing the soil lateral displacement. Site stratification was found to have a potentially highly significant influence on the accumulated lateral ground displacement. The involved localized deformation mechanism may have an important influence on the SC response and efficacy. Overall, the conducted study provides insights for defining an economical and effective remediation solution.

The intermediate principal stress ratio b has a significant influence on the dilatancy behaviors of rockfill materials. The dilatancy equation is defined as a function of the dilatancy d_g and the stress ratio η. To investigate the applicability of a dilatancy equation when considering the influence of the b-value, a series of true triaxial tests including constant b-value (CB) tests and plane strain tests were performed. The results of the CB tests indicated that the stress ratio at the critical state, M_c, remarkably decreases with increasing b-value. By comparing the results with three widely used interpolation functions, a newly proposed interpolation function was suggested to express the relationships between the material constants of the dilatancy equation, i.e., M_c, A, and C, and the Lode angle θ (b-value). Additionally, the predictions of the dilatancy equation considering b-value agreed well with the rearranged test data of the constant-b and plane strain rockfill specimens. As a result, the dilatancy equation and the proposed interpolation function are believed to well express the dilatancy behaviors of rockfill materials under three-dimensional stress conditions.

An improved three-dimensional (3D) displacement measuring system that uses the particle image velocimetry (PIV) technique was developed to measure the full 3D displacement fields around a laterally loaded pile in transparent soil. The reconstructive procedure of 3D displacement fields includes calculation of the two-dimensional (2D) displacement fields, interpolation of 2D displacements, reconstruction of 3D displacement vectors in the intersection points, and interpolation of 3D displacement in the unknown points. A supplementary particle test was conducted to verify the reconstruction of the three components of the displacement of the particles. A model test of a laterally loaded pile in transparent soil was performed to obtain the full 3D soil displacement fields around the pile. The results show that the magnitudes of the displacement vectors and the angles with respect to the x-axis between the displacement vectors obviously decreased not only as the depth increased but also as the distance from the edge of the pile increased. It is highlighted that the depth of the point with the maximum displacement was decreased with respect to the increase in distance from the edge of the pile. This study helps to better understand the interior soil behavior around a laterally loaded pile. The test demonstrates that the full 3D displacement system is suitable for monitoring soil–structure interaction.

The crucial role of intensity measure (IM) selection in the seismic fragility analysis of gravity quay walls is demonstrated in this paper. Scalar- and vector-valued fragility functions are presented for seismic vulnerability and performance-based evaluation of a well-documented gravity quay wall. Nonlinear dynamic analysis by an advanced constitutive model, UBCSAND, was performed to capture earthquake-induced permanent displacement of the quay wall. The estimated permanent displacement and tilting of the wall are in good agreement with its performance observed during the Kobe 1995 earthquake. Numerous dynamic analyses were then performed to compile a database of permanent displacements. Subsequently, a refinement process was conducted to classify the IMs, based on their interdependency and also their efficiency, sufficiency, and predictability. Eventually, the most appropriate IMs along with the most applicable ones were selected as the nominate parameters for seismic fragility analyses. The results demonstrate that the probability of exceedance from a given damage state is strongly dependent on the IMs selected for the fragility analysis. Appropriateness of the selected IMs is discussed through the comparison of the observed damage and the probabilities given by the fragility functions. The fragility functions developed by vector-valued IMs obtain more realistic probability of the quay wall damage compared with the scalar-valued fragility curves.

This study proposed a coupling discrete-element method–finite-element method (DEM-FEM) to investigate the ballast–sleeper interaction under dynamic loading. A surface-coupling algorithm was used to combine the finite-element and discrete-element analyses. A timber sleeper and steel sleeper were selected in the ballast–sleeper interaction analysis. Spherical particles were generated to explore the behaviors of ballast. The porosity of the ballast and the pressure distribution under the sleeper were investigated under the dynamic loading condition. The pressure distribution obtained from the DEM-FEM simulation was compared with the laboratory test. Results showed that the pressure distributions under the timber and steel sleepers were different. Cyclic loading could change the pressure distribution. Validation was performed by comparing experimental results and the numerical results obtained from DEM-FEM modeling. Porosities beneath the steel sleeper were lower than beneath the timber sleeper. For both the timber sleeper and steel sleeper, porosity beneath the rail seat was the lowest, whereas porosity beneath the sleeper end was the largest.

Particle shape properties can significantly affect the load response behavior and field performance of the uniformly graded ballast layer in railway track structures. Particle contact and the related micromechanical behavior of the unbound aggregate ballast layer assembly influenced by the particle shape properties have not yet been thoroughly investigated. In this study, an aggregate imaging and particle shape-analysis approach based on computer vision technology was introduced to calculate aggregate morphological indices and construct polyhedral discrete elements with shapes close to realistic ballast aggregate particles. A model of direct shear test on railway ballast based on the discrete-element method (DEM) was developed using generated nonbreakable discrete elements as individual ballast particles and validated by closely matching the predicted shear stress–strain behavior with laboratory test results. The DEM model simulation predictions were then used to investigate the relations between microscale interactions of individual ballast particles, particle size effects in relation to shear box test equipment dimensions, and macroscale behavior trends of the aggregate assemblies. Stronger particle interactions and higher coordination numbers were observed as the imaging-based angularity index (AI) and flat and elongated (F&E) ratio increased. Furthermore, limiting individual particle movement was shown to increase strength and provide greater resistance to failure and deformation.

Limit equilibrium methods (LEMs) have been widely used for slope stability analysis in engineering practice. The critical slip surface in LEM, which has the minimum factor of safety (FS), is often assumed as the most likely slip surface and subsequently used as the failure slip surface in the analysis and design of slope stabilization measures, such as soil nails and anchors, for unstable slopes. This assumption has not been validated systematically, probably due to the difficulty in simulating large displacement of soils during landslides. In this study, a new mesh-free, particle-based numerical method in geotechnical engineering called smoothed particle hydrodynamics (SPH) is adopted to simulate the entire process of landslides, including the large displacement of soils after a landslide initiates. A series of comparative studies on the stability analysis of cohesive slopes is performed using both LEM and SPH. The comparative studies show that the assumption is reasonable for stable slopes. However, for unstable slopes in which the location of failure slip surface is critically needed for the design of stabilization measures, the LEM critical slip surface differs substantially from the failure slip surface, and the volumes of sliding soil masses are greatly underestimated by the LEM critical slip surfaces. Using the LEM critical slip surface as the failure slip surface in the design leads to the unsafe design of stabilization measures. A new method was proposed to properly locate the failure slip surfaces for unstable slopes when using LEM. It is found that the failure slip surfaces for unstable slopes is not the slip surface with the minimum FS; instead, it is the one with FS = 1.

This article presents an analytical investigation of the dynamic response of a rigid cylinder foundation embedded in a poroviscoelastic soil layer overlaying a rigid bedrock and subjected to vertical time-harmonic loading. First, this soil layer is treated as a liquid-saturated porous continuum and described by Boer’s poroelastic model. Second, based on a technique for the separation of variables, the analytical solution for the amplification factor of displacement of the foundation to this load is derived. This solution is then validated by comparing its reduced results with the reported results of saturated half-space cases. Finally, numerical examples obtained from the present solution are performed to show the effects of the thickness of the soil under the foundation bottom, the liquid–solid coupling coefficient of the soil, and the mass ratio of the foundation on the vibration characteristics of the foundation in the soil. The corresponding analysis results are also included, which can provide theoretical reference for engineering practice.

One of the most important causes of damages in clay core rockfill (CCR) dams is the deterioration of the rockfill material over time and big settlements in the dam body. Therefore, the forecast of the settlements and principal stresses in a CCR dam is extremely important for the safety and future of these important water structures. In this study, changes in the nonlinear behavior of a CCR dam were examined by effects of the various reservoir water heights. Moreover, the geodetic measurements were confirmed with the nonlinear analysis results. Atatürk Dam, which is the largest CCR dam in Turkey, was selected for three-dimensional (3D) nonlinear analyses. First, a 3D finite-difference model of Atatürk Dam was created using the FLAC3D software, which is based on the finite-difference method. A Mohr-Coulomb material model was used for the dam body materials (e.g., clay core, filters, alluvium, rockfill) and foundation for the 3D numerical analyses. Numerical analyses were carried out for five various reservoir water heights: empty reservoir, 50, 100, 153, and 170 m (full reservoir). According to the finite-difference analyses, the effect of various reservoir water heights on the nonlinear behavior of the Atatürk dam was assessed in detail, and how much maximum vertical settlement will occur in the Atatürk Dam body in the future was determined. In addition, principal stresses and horizontal displacements were evaluated for each reservoir condition, and these results were compared with each other. This study demonstrated that as the reservoir water height increased at the upstream side of the dam, the principal stresses and vertical–horizontal deformations occurring in the dam body obviously changed and increased. In the second part of this study, the geodetic vertical settlement results observed by the General Directorate of State Hydraulic Works (DSI) between 1992 and 2013 were presented graphically. These geodetic observation results and numerical analyses were compared in detail, and the geodetic measurement results were confirmed by numerical analysis results.

This paper presents the experimental study on the influence of grouting reinforcement on the fatigue behavior of cracked cement mortar under different stress ratio and levels. The compressive fatigue tests were conducted with a loading frequency of about 150 Hz. The fatigue life decreased logarithmically with the increase of the stress level, and the fatigue life threshold increased with the increase of the stress ratio. The pores near the fracture were effectively strengthened after the grouting reinforcement. The initial fatigue crack of the sample was initiated at the original crack tip when the lateral deformation reached its threshold value. A double logarithmic fatigue equation was introduced to delineate the fatigue equation. Considering the influence of stress level and stress ratio, a damage evolution equation was proposed to describe the damage evolution process. The fitting results agreed well with the test data.

This article presents an analytical solution to predict the deformation of a geosynthetic-encased stone column (GESC) and the surrounding soil using a cylindrical cavity-expansion model. The cavity-expansion model is used to analyze the relationship between the expansion pressure and the radial displacement. The stress and deformation development are analyzed according to the radial stress and the vertical stress equilibrium. This method has been verified via comparison with field-test data in the literature. Parametric studies were conducted to investigate the influences of applied loading, geosynthetic encasement stiffness, soil stiffness, and encasement length on the mechanical performance of the GESC and the surrounding soil. The results indicate that the radial displacement of the soil decreased sharply and became zero at a relatively large distance from the column. At the radial position of 5 times the radius of the GESC, the radial displacement of soil was almost 0.2 times the column radial displacement.

The cement asphalt (CA) mortar layer acts as the key component of the China Railway Track System II (CRTS-II) type ballastless slab track to ensure stability, durability, and cost maintenance. However, it was found to be easily degraded during operation, particularly under extreme climate conditions. In this paper, to study the performance of CA mortar under extreme temperatures, flexural strength and fatigue tests were conducted to evaluate its mechanical properties. Moreover, the stress and deformation of the track under different temperature loads were analyzed based on the temperature fields, which were simulated through a transient thermal analysis. The results show that the flexural strength and fatigue life are reduced by high temperatures, and the highest possible temperature on the surface of the track can reach 58.8°C in China. The maximum principle stress can reach 1.2 MPa under the negative temperature gradient load, which is three times larger than under the train load and is close to the flexural strength obtained from the tests. As a result, the degradation of CA mortar is mainly caused by the increase of the stress and the deterioration of the tensile capacity induced by the extreme climate.

The study unfurls the analysis of interfacial imperfections on Rayleigh waves transmitting through micropolar thermoelastic solid without energy dissipation over a semi-infinite isotropic thermoelastic solid in context of dual-phase-lag model. Separate analytical expressions regarding displacements and thermal stresses have been derived in order to characterize the dynamics of individual materials. Taking the free surface as thermally insulated and traction free, suitable spring boundary conditions on account of imperfect interfaces have been used upon the surface wave solutions of elastodynamical equations pertinent to those materials. From the real part of eleventh-order determinantal expression, we obtain the frequency equation of Rayleigh waves for the proposed earth model. Some special cases of boundaries i.e., normal stiffness, transverse stiffness, thermal contact conductance, slip boundary have been deduced from the imperfect one. Numerical computations have been performed in order to graphically illustrate the dependencies of different boundaries and phase lag on the phase velocity of Rayleigh waves. The study may find potential applications in fields of naval architecture and aeronautics where temperature induced elastic deformations occur.

In this study, a series of numerical pullout tests was performed using the discrete-element method (DEM) to investigate the micromechanical behavior of geogrid pullout and the effect of geogrid tensile stiffness. Geogrid–soil interaction during pullout was investigated not only through displacement fields and force chains inside the soil but also via the quantitative displacement and force distributions along the geogrid. The active and inactive zones were defined based on the displacement fields in the soil, and the displacement corresponding to the boundary between the active and inactive zones was found to be 1.25 mm in this study. The higher the geogrid stiffness, the larger was the thickness and length of the active zone mobilized in the soil under the same pullout displacements. The thickness and length for the geogrid with largest tensile stiffness were 150 and 500 mm (full length of geogrid), respectively. Reorientations of contacts and forces within both the inactive and active zones were further visualized based on the Fourier-series approximation. The part of the geogrid that experienced displacement of more than 1.25 mm (used for the definition of the active zone) is defined as the affected part, and its corresponding length is defined as the affected length. The stiffer geogrid was found to activate the affected length into the full range more rapidly than the less stiff one prior to failure. The tensile forces at the load ends of stiff geogrids were larger than those at the load ends of extensible geogrids at all given pullout displacements.

A good understanding of rock mass behavior around underground tunnels is necessary for stability assessment and support design. This paper presents a three-dimensional (3D) numerical analysis to support the aforementioned statement for an underground mine by using the distinct element method. Geological and engineering complexities simulated in the numerical model include large-scale faults and a nonplanar weak interlayer, as well as open and backfilled tunnels. Sequential excavation, backfilling, and delayed supporting were simulated according to the field construction process. Numerical analysis investigated the effect of complex geologies and engineering activities on tunnel stability. Deformations and strength degradation areas around the tunnels are illustrated and analyzed at different locations. Based on the rock mass behavior and the failure conditions of the applied rock supports, useful suggestions are made on the selection of appropriate tunnel support for this underground mine. These suggestions shared similarities and slight differences with the guidelines suggested by an empirical method. The accuracy of the numerical results is verified by comparing with the field deformation data. This study provides a comprehensive procedure for stability assessment and support design for similar underground rock mass projects.

A new failure mechanism established from a streamline velocity field with energy dissipation through an internal deformable zone and the velocity discontinuity at its boundary is proposed. The application of the developed velocity field to the upper-bound theorem stability analysis of a shallow circular tunnel in nonhomogeneous undrained clay with a linear strength gradient of depth is further demonstrated. Comparisons of stability upper-bounds are made among the current mechanism with other reported solutions to verify the present method. A discussion on the optimal failure mechanism and the corresponding velocity field is presented.

In geotechnical engineering, fracture fillings or rough fracture surfaces often resist deformation and enhance the equivalent elastic moduli of fractured rock masses. In this study, the normal stiffness and shear stiffness of penny-shaped fractures were incorporated into the open-fracture model to account for the normal and shear resistance of fracture fillings. Based on the derived displacements of a penny-shaped fracture incorporating fracture stiffness, the compliance matrices of two special fracture distributions, the parallel distribution and random distribution, were obtained. The analytical results show that three-dimensional (3D) models predicted larger elastic moduli than the corresponding two-dimensional (2D) models, and models considering fracture stiffness predicted larger elastic moduli than the open-fracture models. Elastic moduli were underestimated by 30–40% in a 2D open-fracture model compared with the result of the corresponding 3D model. The difference in elastic moduli between 2D and 3D models was found to decrease when the fracture stiffness was considered. In the present study, the difference was less than 15%.

In the last few decades, many experimental and a few numerical investigations were performed to investigate the behavior of strip footing placed on the soil slope. However, most of the previous studies were case specific. Thus, due to the nonavailability of the design charts for the computation of the bearing capacity of strip footing placed on the edge of the slope reinforced with more than one layer of reinforcement, the authors were impelled to conduct the present study. The effect of the interface friction angle between soil and reinforcement, which seems to have a significant effect on the bearing capacity of strip footing, also is not considered in the previous studies. By using the lower bound finite-element limit analysis technique, a set of design charts are prepared to compute the bearing capacity of a strip footing placed on the top of a cohesionless soil slope reinforced with two layers of reinforcement. The effect of (1) slope angle (β), (2) soil friction angle (ϕ), (3) depth of the first layer of reinforcement from the footing base (d₁/B), (4) depth of the second layer of reinforcement (d₂/B) from the first layer of reinforcement, and (5) interface friction angle between cohesionless soil and reinforcement layer (δ) are considered during the analysis. As expected, with the addition of a reinforcement layer, the bearing capacity increases. The efficacy of the reinforcement layer is quantified in terms of η_γ, which is the ratio between the N_γ values obtained for the reinforced and unreinforced slopes. The value of efficiency factor increases up to a certain value of d₁/B for a single layer of reinforcement and d₁/B and d₂/B for a double layer of reinforcement; after that it reduces. Because of the reduction in the magnitude of δ for single and double reinforced slopes, the effectiveness of the reinforcement decreases. The axial tension (T) generated due to the friction between the moving soil particles and reinforcement is also plotted throughout the reinforcement layer. One can easily compute the optimum length (L_opt) of the reinforcement required to avert tensile failure from these graphs. The effect of soil dilatancy on the bearing capacity of strip footing placed on the double reinforced slope is investigated for a number of cases. Failure patterns are also plotted for a better understanding of the failure mechanisms of strip footing placed on the edge of the reinforced cohesionless soil slope.