International Journal of Geomechanics

Loss of fine particles or suffusion in soils induced by seepage is an important problem that may cause dam or dike failures. This paper aims to study the evolution mechanisms of suffusion in gap-graded sandy gravels using coupled computational fluid dynamics and discrete-element method (CFD-DEM). In the simulation, five groups of sandy gravel including four groups of gap-graded sandy gravel and a benchmark linearly graded sandy gravel were studied. Changes in flow rate, evolution of porosity in different layers, and spatial and temporal redistributions of particles in the samples during suffusion under upward seepage were studied. Simulation results show that when the fine particle content is the same, the total fine erosion ratio is larger when the stability index ${(H/F)}_{\min }$ of the gap-graded sandy gravel is lower. The porosities of five layers of the gap-graded sandy gravel change continuously with infiltration time. A slight decrease in the fine grain content appears in the upper layers, while a sharp reduction in the fine grain content occurs in the bottom layer. The study provides a mechanics basis for the prediction and prevention of suffusion in gap-graded sandy gravels.

The aim of this study is to investigate the uplift behavior of horizontal strip plate anchors constructed at a distance to the slope crest. A series of uplift load tests was conducted in laboratory for scaled strip plate anchor models, which were buried in the horizontal ground or at different distances from a sand slope with various slope angles. Results imply that the distance from the anchor to the slope and the angle of the slope play an influential role in the failure mode and loading capacity. The loading mechanism of the strip plate anchor buried near a slope is equivalent to that of a strip plate anchor buried in horizontal ground when the edge-distance ratio reaches a critical value. The critical edge-distance ratio obtained by the proposed formula in this study is 0.9 or 1.9 for slope angles of 15° or 30°, respectively. Further, the geometric configuration of the failure surfaces can be approximated to be circular curves whose radius can be determined by the value of edge-distance ratio and slope angle. After that, an analytical method to calculate the uplift capacity considering the influence of edge-distance ratio and slope angle has been developed by using the limit-equilibrium method. All the error between the calculated results based on the theoretical solutions and the measurements from the laboratory tests is contained in 17.4% when the effect of sand dilatancy is considered.

Biplanar failure is the most common instability type of footwall slopes, with a steeply dipping joint (typically the bedding plane) and a gently dipping joint (i.e., the daylighting toe joint) forming the basic failure surface. Limit equilibrium, due to its high efficiency and accuracy, is a widespread method in the analysis of such a failure. In this paper, a new block model of biplanar failure is first proposed on the basis of the interaction mechanisms between the active and passive blocks. Then, considering the orientation of the interblock boundary, a biplanar failure analysis method (BFAM) is presented that satisfies both the force and moment equilibrium conditions. Subsequently, a simplified biplanar failure analysis method (SBFAM) is also proposed for ease of use. Finally, parametric analysis was carried out to investigate the influence of the sliding mass depth, slope height, dip angles, and shear strength of the joints on slope stability. It was found that the safety factors of the footwall slope obtained using the BFAM approach are generally consistent with those found using the Morgenstern-Price and Spencer methods. Additionally, the safety factors using the SBFAM approach are well consistent with the physical modeling and BFAM results.

This paper presents a study on the deformation and degradation responses of railway ballast using large-scale laboratory testing and computational modeling approaches. A series of large-scale triaxial tests were carried out to investigate the ballast breakage responses under cyclic train loading subjected to varying frequencies, $f=10–40\mathrm{Hz}$. The role of recycled rubber energy-absorbing mats (REAMs) on reducing ballast breakage was also examined. Laboratory test results show that the ballast experiences significant degradation (breakage) and deformation, while the inclusion of REAMs can reduce the ballast breakage up to about 35%. Numerical modeling using the coupled discrete-continuum approach [coupled discrete-element method–finite-difference method (DEM-FDM)] is introduced to provide insightful understanding on the deformation and breaking of ballast under cyclic loading. Discrete ballast grains were simulated by bonding of many circular elements together at appropriate sizes and locations. Selected cylinders located at corners, surfaces, and sharp edges of the simulated particles were connected by parallel bonds; and when those bonds were broken, they were considered to represent ballast breakage. The subgrade and rubber mat were simulated as a continuum media using FDM. The predicted axial strain ${\epsilon }_a$ and volumetric strain ${\epsilon }_v$ obtained from the coupled DEM-FDM model are in good agreement with those measured in the laboratory. The model was then used to explore micromechanical aspects of ballast aggregates including the evolution of particle breakage, contact force distributions, and orientation of contacts during cyclic loading. These findings are imperative for a more insightful understanding of the breakage behavior of ballast from the perspective of microstructure characteristics of discrete particle assemblies.

The granular cushion has been increasingly used as a load transfer platform between a column foundation and a raft to ensure appropriate contact and load transfer among the raft, the columns, and the soil. However, deformation compatibility and load transfer mechanisms of the cushion have not been well studied. A series of two-dimensional (2D) model tests with different cushion thicknesses and column widths were carried out to investigate the load transfer mechanisms of the cushion using a multitrapdoor apparatus. Deformation characteristics and slip surfaces were observed during the tests, and the observations indicate that the diffusion cone model is applicable, especially when the relative cushion thickness and the relative column net spacing are large. The measured load efficiency decreased with the increase in the relative cushion thickness and the relative column net spacing. This paper presents the calculated pressure diffusion angle on the columns, analyzes the distribution of the contact pressure between the raft and the cushion, and establishes the methods for evaluating the contact pressure distribution and the load efficiency of the column foundation.

Buildings constructed adjacent to the slope crest in seismically active areas might be exposed to serious danger when they are subjected to strong earthquake excitations. The ground conditions can influence the seismic response of structures through a phenomenon known as the slope–foundation–structure interaction. Indeed, the presence of the slope in the vicinity of a building foundation can significantly affect the seismic response of the superstructure. In this study, the impact of shallow slopes on the seismic performance of nearby buildings was numerically assessed. In the adopted three-dimensional finite-element simulation, the nonlinear variations of the soil stiffness and damping with the cyclic shear strain plus varying distances between the edge of the foundation and crest of the slope were employed. A 15-story moment-resisting structure, a 30-m-thick clayey deposit, and a 2-m-high shallow slope were considered as the benchmark model, being simulated using the direct method in the time domain. According to the results of the analyses, the seismic response of a building could be highly sensitive to the distance between the slope crest and foundation. Particularly, the building closer to the slope crest experienced more severe foundation rocking, lateral deformation, and interstory drifts owing to the amplified effect of the slope–foundation–structure interaction. Moreover, the results highlighted the importance of the slope–foundation–structure interaction in altering the natural period and damping of the system. Hence, it is critical for practicing engineers to assess the impact of nearby slopes on the seismic performance of structures with extreme care to ensure the reliability and safety of the design.

This article is framed to examine the influence of heterogeneities, viscosity, initial stress, rigidity and density ratios, and thickness on traversal characteristics of Love-type surface wave in a heterogeneous anisotropic medium over heterogeneous Voigt-type viscoelastic functionally graded material (FGM) orthotropic half-space influenced by a point source. The rigidity and density of the anisotropic layer are considered to vary hyperbolically with depth, whereas the density, elastic parameter, initial stress, and viscoelastic coefficient for the semi-infinite stratum are assumed to vary quadratically with depth. The complex velocity of the Love-type wave has been achieved by the method of Green’s function and Fourier transformation under effective boundary conditions. After complex expansion of the velocity equation, we get the dispersion and absorption relations from the real and imaginary parts, respectively. In some special cases, we have derived the classical relation of Love wave for the case when both the anisotropic layer and viscoelastic half-space are isotropic and homogeneous, which validates the assumed problem. Numerical solutions have been carried out and depicted graphically to elucidate the effect of these parameters on the traversal characteristics of a Love-type wave. The appearance of heterogeneities, initial stress, and viscoelasticity in the velocity equation reflects that these parameters significantly affect the attenuation and dispersion characteristics of Love-type waves.

Particle breakage is a common phenomenon in granular soils and has been well observed during laboratory and in-situ pile studies. In this paper, an image analysis approach was developed to investigate the particle breakage behavior below a flat-ended pile tip, with special attention given to the location of particle breakage. The color difference between the original silica sand (light gray) and its coated surface (black) allows particle breakage to be distinguished based on the gray level variation. Larger gray values corresponded to a higher degree of breakage that occurred within the target area, which provides a new approach for quantitative assessment of the particle breakage extent. First, sequential images of the subsoil at different depths below a loaded pile tip were digitally recorded, and the degree of particle breakage was subsequently evaluated based on the gray level of the images. Then, the layered images at different depths were assembled to form a quasistereoscopic graph, and the slice image at any profile could be obtained. Accordingly, the zone of particle breakage below a flat-ended pile tip was graphically illustrated. The results of this study are beneficial for further clarifying the mechanism of particle breakage and provide a fundamental basis for accurate assessment of the ground-bearing capacity considering soil crushability.

Subsea pipelines are commonly used for transportation of hot hydrocarbons from offshore sites. The temperature difference between the hot pipeline and the cold seabed induces thermal loads. Temperature effects on the hydromechanical response of a seabed have been overlooked in the majority of previous studies. In this paper, a framework based on isogeometric analysis (IGA) is employed for fully coupled modeling of thermo-hydromechanical (THM) processes in saturated subsea soil subjected to harmonic hydraulic loading conditions. The latter enables the model to take into account the tide-induced pore pressure that is particularly important for design purposes. The proposed IGA-based model offers interelement connectivity and can benefit from a high-order degree of approximation in the simulation of nonlinear problems. Bézier extraction is used to integrate IGA with the finite-element method in the proposed framework. A two-dimensional model is used to investigate the seabed response during three phases: pipeline postinstallation (Phase 1), operation conditions (Phase 2), and shutdown period (Phase 3). Phase 1 represents the isothermal behavior of subsea soil during a short postinstallation period. Phase 2 corresponds to a relatively long nonisothermal operational period and Phase 3 simulates the nonisothermal behavior of seabed in the shutdown period. The results show the induced thermal gradient changes the horizontal deformations from negative to positive and vice versa during the long-term operational (Phase 2) and shutdown (Phase 3) periods, respectively. Incorporating the thermal effects into the simulation changes the seabed response from rotational mode in isothermal conditions to sliding mode in nonisothermal conditions.

The vibration prediction of a vehicle-track-tunnel-soil dynamic system is quite meaningful in engineering practice. However, the complexity involved in modeling the underground environment makes most previous studies ignore the impact of a neighboring tunnel. In this paper, a three-dimensional analytical model is presented to predict the vibrations of the vehicle-track-tunnel-soil system in a poroelastic half-space, with the dynamic interaction of two neighboring tunnels being considered. The vehicle was considered as a multibody system, and the slab and rail were simulated as Euler–Bernoulli beams. The twin tunnels were simplified as cylindrical thin shells, and the soil surrounding the tunnel was simulated as a saturated porous medium. Wave translation and transformation were applied to satisfy the boundary conditions of the interfaces between the tunnels and soil as well as the ground surface. By coupling the twin-tunnel model with the vehicle-track model, an analytical model for the vehicle-track-tunnel-soil system was obtained. The proposed model was validated by means of comparison with the existing solution. The numerical results demonstrate that the neighboring tunnel and water saturation have a significant effect on soil vibrations.

Step-shaped slopes are often found in mines. The reliability of step-shaped slopes was investigated based on random field models. The factor of safety of slopes was derived by the horizontal and vertical integration methods. Meanwhile, the cohesion and friction angle along the discontinuity failure surface were treated as random variables that were assumed to follow Gaussian random distribution. The effects of spatial correlation and cross-correlation between parameters on the stability of step-shaped slopes were taken into consideration. A closed-form solution for the probability of failure ($P_f$) of step-shaped slopes was finally derived. It was found that the derived $P_f$ was greatly affected by the input spatial correlation length of geomechanical parameters. The effectiveness of the proposed method was validated using Monte Carlo simulations.

Limited by the particle size requirements of testing apparatus, little true triaxial test (TTT) research on rockfill has been conducted. Using a large true triaxial apparatus (TTA) developed independently by the Changjiang River Scientific Research Institute (CRSRI), tests with different intermediate principal stress ratios {Ratio $b[=({\sigma }_2-{\sigma }_3)/({\sigma }_1-{\sigma }_3)]$} and plane strain tests were carried out on sandstone rockfill. The results show that, with the same Ratio $b$, the initial slope in stress-strain curves and peak stress increased with rising ${\sigma }_3$; with low ${\sigma }_3$, volumetric strain first contracted and then transitioned to dilatancy; with high ${\sigma }_3$, it continued to contract throughout the deformation process. With stable ${\sigma }_3$ but increasing Ratio $b$, softening and brittle failure after peak stress were obvious and the strain corresponding to peak stress slightly lagged behind the strain bending point in the ${\epsilon }_1–{\epsilon }_v$ curves, which reflected deformation and failure of the specimen force chain. The effect of Ratio $b$ in increasing strength was significant, especially in the range 0–0.25, where strength showed significant growth. The Lade–Duncan failure criterion was more suited to revealing strength evolution than were other criteria, but both ${\sigma }_3$ and Ratio $b$ induced significant particle breakage. The actual tested strength was always lower than the estimated strength obtained by the Lade–Duncan failure criterion. Under plane strain, when deviatoric stress approached its peak value, Ratio $b$ was around 0.17–0.19 in all tested specimens. The contribution of ${\sigma }_2$ in increasing specimen strength was basically reflected. This means that, when test conditions are limited, the plane strain test can be used to make a rough estimate of the strength index of rockfill under complex three-directional stress.

Prediction of rockburst involves numerous random and fuzzy indicators asymmetrically distributed in finite intervals. Herein, a novel multidimensional connection cloud model was introduced to depict uncertainties and distribution characteristics of indicators, and the fuzziness of the classification boundary. In the model, numerical characteristics of the connection cloud model were first determined on the basis of the set pair analysis (SPA) of measured indicators relative to the classification standard. Then a multidimensional connection cloud model was presented to express the interval-valued classification standard. Next, based on the combination weight specified by a distance function, the integrated connection degree for a grade was identified for the sample. Finally, a case study and comparison of the proposed model with the normal cloud model and extensible evaluation method were performed to confirm the validity and reliability of the proposed model. The results show that the proposed model, with a quicker and simpler calculation process than a normal cloud model, can describe the multiple types of uncertainties of interval-valued indicators and overcome the subjectivity when determining numerical characteristics of the cloud model.

Slender single piles are extensively used but susceptible to buckling when embedded in soft ground mediums. Owing to the complexity of soil properties, the soil-structure interaction (SSI) response is sometimes very complicated, but its consideration is essential in the design of slender piles. Current design practice relies on either empirical-based linear analysis approaches or sophisticated finite-element methods, which are overconservative or time-consuming, respectively. Therefore, this paper derives a new Euler-Bernoulli element by adopting Winkler-type continuous springs along the element length for considering SSI responses, eliminating the need to model the ground mediums. Consequentially, this method is numerically very efficient, being suitable for the practical analyses of large-scale structures with the explicit modeling of upper structures and piles. A Newton-Raphson incremental-iterative numerical procedure is developed for determining the equilibrium conditions, where the tangent stiffness matrix and the secant relations are formulated using the Gauss-Legendre method for solving the summation procedures. For allowing large deflections, the kinematic motions described by the updated Lagrangian (UL) method are proposed, where the equilibrium conditions are established by referring the last known configurations. Finally, several benchmark examples are provided for validating the accuracy of the proposed method.

In this paper, mudstone in coal measure rock strata was investigated to understand the brittle–ductile transition characteristics of mudstone under high temperature. An electrohydraulic servo system, high-temperature furnace, and scanning electron microscope were used during high-temperature mechanical tests and scanning electron microscopy experiments which focused on studying the effects of temperature on the yield strain, peak strain, ductility coefficient, and stress–strain relationship of mudstone. The results showed that, for the most part, the yield strain of mudstone first increased and then decreased as temperature increased. At temperatures below 700°C, the mudstone was primarily brittle, and at about 800°C, the brittle–ductile transition of the mudstone occurred under the effects of high temperature. At this transition temperature, granular cracks, intergranular cracks, and transgranular cracks in the mudstone crystal formed a large crack network structure, and the mudstone samples showed ductile failure characteristics.