International Journal of Geomechanics

The dynamic properties of mixtures of poorly graded sand and the fine rubber tire chips are assessed under undrained, strain-controlled cyclic simple shear (CSS) conditions. In this study, CSS equipment with a confining pressure system is used. The CSS tests are performed on the mixtures with rubber content of 0%, 10%, 30%, 50%, and 100% by weight prepared at relative densities in the range of 65%–80%. Tests are carried out at high shear strain amplitudes in the range of 0.15%–3% at various total vertical stress levels (50–200 kPa). The material and loading parameters such as rubber content, shear strain, frequency, total vertical stress, influencing the dynamic properties and the pore pressure responses of the mixtures are investigated. It was found that the mixture with 10% rubber content has better dynamic properties than other mixtures. In addition, the pore pressure development can be retarded by the use of the sand–rubber tire chip mixtures.

More and more oceanic projects involve calcareous sand–marine clay mixtures which behave totally different from pure calcareous sand and marine clay. The effect of clay content on the compression behavior of the calcareous sand–marine clay mixture is investigated in this study. The results reveal that the coefficient of volumetric compressibility m_v will be affected significantly by the clay content at low stress state (i.e., vertical stress less than 600 kPa), but the influence of the clay content on m_v can be neglected at high stress states. Further laboratory tests found that the effect of clay content on the creep behavior is negligible for a marine clay fraction of 30% or less, but the effect increases with clay contents larger than 30%. In addition, the particle breakage characteristics are investigated from particle size distributions before and after application of loading in oedometer tests. A general correlation is obtained from the test data to evaluate particle breakage ratio B_r by clay content r and magnitude of load p. Finally, a modified conceptual model based on Lade’s transitional fine content (TFC) model is proposed to predict the transitional state of the mixture by considering volume change induced by the sand breakage. The model is used to analyze the critical clay content at transitional state based on some reasonable assumptions and a very good prediction can be obtained.

Increasing hydraulic gradients and associated seepage in a soil foundation accompanied by a reduction in effective stress, degradation of soil stiffness, and diminished internal stability contribute to adverse conditions in engineered earth structures, including dams and transport infrastructure. Although much attention has been drawn into these geotechnical challenges, most previous analytical and experimental studies could not properly capture the detailed response of fluid and soil particles, especially the localized or microscopic fluid–soil perspectives. In this regard, this paper aims to apply a numerical approach to analyze the response of a soil–fluid system under increasing hydraulic gradients. Soils with different gradation properties and porosities are created using the discrete element method (DEM), which is then coupled with computational fluid dynamics (CFD) based on Navier-Stokes equations. This numerical investigation reveals different stages in the development of hydraulic critical state, that is, from localized erosion (e.g., piping) to overall heave and fluidization. The transformation of fluid and particle characteristics, such as particle migration, the erosion rate, and hydraulic conductivity associated with porosity when soil approaches critical state, is discussed in detail. Micromechanical degradation within the contact network and the associated reduction in effective stress of soil due to an increasing hydraulic gradient are also analyzed in this study. A number of key factors that govern the soil response, such as friction, porosity, and grain uniformity, are addressed through numerical investigations. This study demonstrates acceptable numerical predictions for hydraulic behavior and erosion rates that are in good agreement with previous experimental data.

Cantilever sheet pile walls are generally designed assuming the rectilinear distribution of net earth pressure. In this paper, a new method is proposed in the framework of the limit equilibrium approach for the analysis of cantilever sheet pile walls with distanced infinite uniform surcharge load under the seismic condition in cohesionless soils. The sheet pile wall is assumed to be a rigid body to rotate about a pivot point near the toe of the wall and generates active and passive earth pressures. Horizontal force equilibrium and moment equilibrium are considered to determine the pivot point simultaneously. Closed form expressions for the bending moment and shear force at various depths of the sheet pile wall are proposed. It is observed that for a horizontal seismic acceleration coefficient of 0.3, and when the magnitude of surcharge increases from 0 to 100 kPa, the penetration depth increases by 103.75% and 64.7% when the surcharge is placed at the top and at 3.9 m away from the sheet pile wall, respectively. The requirement of the penetration depth and corresponding location of pivot point based on the magnitude and location of the surcharge is proposed through design charts in nondimensional form.

Untreated soil is prone to erosion and dust generation that result in various environmental and health hazards. The addition of additives has been used as a soil treatment method to tackle this problem. Conventional techniques such as chemical additives impose negative ecological impacts and significant implementation and maintenance costs. This paper evaluates the efficiency of three eco-friendly biopolymers, xanthan gum, guar gum, and carboxymethyl cellulose (CMC) with 0.5%, 1%, and 1.5% concentrations for soil treatment against dust generation. This study also investigates the long-term performance and durability of biopolymers. Three types of samples (dust particles) were collected from different locations that generate the most dust in Iran: Hooralazim lagoon as a source of soil, Urmia lake bed as a source of saline sand, and Sungun copper mine as a source of mine tailing. Approximately 500 samples prepared and treated with different biopolymer concentrations were evaluated by the wind tunnel, moisture retention, surface strength, and uniaxial compression tests to identify the most effective biopolymer. The addition of biopolymers improved moisture retention, surface strength, compressive strength, and mitigation of dust generation. Scanning electron microscopy (SEM) imaging was also used to study the microstructures of the specimens after treatment. A strong correlation was found between the weight loss after the wind tunnel test versus the maximum penetration force and the uniaxial compressive strength. In terms of dust generation preventive treatment, CMC was more effective than xanthan gum and guar gum. Hence, CMC was introduced as an alternative material for dust control due to its promising potentials.

To better understand the shear behavior of infilled rock joints with standard joint roughness coefficient (JRC) profiles, direct shear experiments are performed on sand and clay infilled joints prepared by reproducing the standard JRC profiles on a rock-like material and placing the infill material inside the joint. The results show that the shear behavior and strength of infilled joints are affected by the JRC, the infill material type, the infill thickness to joint asperity amplitude (t/a) ratio, and the applied normal stress. For most of the infilled joints, the shear stress versus shear displacement curve shows a residual shear stress value close to the peak value and no softening phase. The normal displacement of infilled joints shows pure compression or first compression and then dilatation. Under the same normal stress, the clean joints show the largest shear strength, followed by the sand infilled joints, and then the clay infilled joints. The peak shear strength of infilled joints decreases with larger t/a, following a nearly negative exponential relation, and reaches the shear strength value of the infill material when t/a is above a certain value. A revised shear strength model for infilled joints was proposed by incorporating the negative exponential relationship between friction angle and t/a in the Barton and Choubey shear strength criterion under constant normal load (CNL) condition. The good agreement between the prediction results from the revised shear strength model and experimental data indicates its capability in estimating the peak shear strength of infilled rock joints.

Saturated soils with overlying dry layers are frequently encountered in geotechnical engineering. In urban construction works, the underground water level is usually influenced by the extraction of water or complex fluid for industrial uses or oil exploitation tasks. The creep and consolidation behavior of saturated soils with overlying dry layers is drastically different from that of completely saturated soils. This paper presents an investigation on the creep and consolidation behavior of the layered saturated soils with overlying dry layers under the vertical load. With the aid of the Laplace–Hankel transform, typical viscoelastic models (e.g., the Kelvin, the Maxwell, or the standard linear solid model), and the correspondence principle, a semianalytical solution is presented for this investigation. Detailed comparisons between the present results with the published numerical and analytical results are given to confirm the solution, followed by an extensive parametric study examining the effect of types of viscoelastic models, thickness of the overlying layer, and viscosity. This paper aims to present a semianalytical solution to describe the time-dependent consolidation of layered saturated soils with the overlying layer accurately and to provide useful implications for foundation design on those soils.

A viscoplastic model is presented for creep and strain rate behavior of soils with particular reference to capturing drained, undrained, primary, and tertiary creep. The model is formulated in the context of the bounding surface plasticity using the consistency viscoplastic framework and the critical state theory. The formulation proposed enables capturing the accumulation of viscoplastic strains upon loading and unloading as well as creep rupture observed in overconsolidated clay. The time-dependency of the soil response is accounted for by defining the size of the bounding surface as a function of viscoplastic volumetric strain and strain rate. The model meets the consistency condition and allows for a smooth transition from rate-dependent viscoplasticity to rate-independent plasticity. Simulation results and comparisons with experimental test data are presented for several drained and undrained creep tests, constant strain rate tests, and stress relaxation tests, to demonstrate the application of the constitutive model.

Installation of a stone column in loose soil is one of the robotics ground enhancement techniques that reduce the risk liquefaction and related ground deformation. However, the experimental investigation is costly and it is time-consuming to check the feasibility of this technique for the evaluation of ground subsidence and fluctuations in excess pore water pressure concerning different area ratios of a high modulus column. This paper presents a numerical investigation into shallow foundations underlain by a stone column as a liquefaction countermeasure. The Biot's consolidation equations are coupled with stress equilibrium equations in finite element modeling for cyclic loading conditions. The critical state model based on generalized plasticity theory was applied to model the nonlinear behavior of soil. The unknown displacement and pore pressure are evaluated using code written in FORTRAN 90. The granular column installation effect is also considered to predict displacements and excess pore pressure (EPP) at each time step. With the introduction of a granular column, considerable reductions were observed in displacements and EPP. The results underline the effectiveness of granular column installation as an effective measure in the mitigation of liquefaction.

Knowledge of fracture process is critical for understanding rock failure mechanisms. In this study, the fracture behavior of single-flawed rock-like material plates made of mortar was investigated using a Split Hopkinson Pressure Bar (SHPB) system. The transient fracture process was recorded by an ultra-high-speed camera system in combination with the digital image correlation (DIC) method. The experimental result reveals that the dynamic strength is more sensitive to the loading rate for specimens with lower flaw angles. Through quantitative analysis of the displacement evolution along the fracture trajectory, four fracture modes were proposed: pure tensile mode (T-mode), pure shear mode (S-mode), tensile dominated mode (Ts-mode), and shear-dominated mode (St-mode). Moreover, it was recognized that the fracture mode is mainly controlled by the fracture angle. As the fracture angle increases, the shear component increases while the tension component diminishes. The results of this study can shed light on the fracture behavior of flawed rocks subjected to dynamic loading.

The creep of soft rocks induced by seepage-stress coupling is one of the critical factors that causes the failure of the rock. However, the actual failure mechanisms of soft rocks, particularly during the accelerated creep stage, have not been fully understood so far. Therefore, the purpose of the present study is to develop theoretical models to quantitively investigate the effects of coupled fissure-pore seepage and hydro-mechanical coupling on the damage behavior of soft rocks. The evolution model of coupled fissure-pore seepage in soft rock was developed, and the coupled fissure-pore damage creep model of soft rock was established. The developed models were also validated by performing a series of triaxial experimental tests. The results show that the theoretical prediction agrees with the experimental results reasonably well. In addition, the developed hydro-mechanical coupled damage creep model for soft rocks can reproduce the experimentally observed deformation behavior of soft rocks in three different creep stages (i.e., deceleration creep, constant creep, and accelerated creep), respectively. Furthermore, the developed fracture evolution and pore index model have the capability of capturing the experimentally observed fracture propagation of soft rocks under hydro-mechanical conditions. The developed model could potentially be used as a useful tool for quantitatively analyzing the risks of soft rock disasters.

Micropiles are an effective option to enhance the load-carrying performance of buildings and infrastructure. In this study, the compressive load capacity and load-carrying mechanism of inclined micropiles in soil and rock layers were investigated experimentally and analytically. A series of model load tests was conducted using model micropiles and rock specimens. The finite element analyses were performed for inclined micropiles in various soil-rock layer configurations. Vertical micropiles in rock exhibited the highest load-carrying capacity whereas inclined conditions were not beneficial. For the rock-mounted condition, the base capacity dominated the total load capacity when the inclination was lower than 15°. For partially and fully rock-embedded conditions, the main load-carrying component was the skin friction and virtually no load was transferred to the micropile base. Micropile inclination caused less mobilization of skin friction within the rock-embedded zone. Instead, the passive resistance within the upper sand layer dominated the overall load capacity, which explained decreasing load capacity with increasing inclination for a rock-embedded condition.

Failure characteristics of rocks under different loading and unloading conditions have been an important subject of laboratory tests. This study aims to investigate the influence of the height to diameter (H/D) ratio on the failure characteristics of marble specimens under unloading conditions. Conventional triaxial unloading (TU) tests were performed on marble specimens of 50 mm diameter with different H/D ratios from 0.5 to 3.0. Moreover, for comparison, uniaxial compression (UC) tests and conventional triaxial compression (TC) tests were conducted on marble specimens with different H/D ratios. The results indicate that the failure strengths of the specimens, including the UC strength, TC strength, and TU strength decrease with the increase in specimen height, and the decreasing trend can be fitted with a function that is deduced from Weibull's theory. The specimens with lower H/D ratios (0.5 and 1.0) underwent tensile failures in the TU tests, whereas the specimens with higher H/D ratios (2.0 and 3.0) showed shear failures in the TU tests. In addition, the analyses of strain energy evolutions indicate that the unloading failures of the specimens with lower H/D ratios are an ongoing process and the unloading failures of the specimens with higher H/D ratios present a sudden process.

Suction caissons, widely applied in offshore engineering, suffer from significant uncertainties about the flow mechanism of the surrounding soil during installation, especially for caissons with ring stiffeners. Large deformation finite element (LDFE) analyses are carried out to investigate the behavior of stiffened caisson by visualizing the soil flow mechanism during the caisson penetration. The LDFE method was first validated against centrifuge test data and good agreement was obtained. A systematic and detailed parametric study was then conducted by considering a large variety of parameters, including stiffened caisson geometry, interface friction coefficient, and soil shear strength. The results show that the ratio of caisson diameter to stiffener width and the normalized soil strength has a significant influence on the soil flow mechanisms. The definitions of critical rotational soil flow depth (H_r) and the limiting cavity depth (H_c) were employed to quantitatively describe the behavior of the observed soil flow mechanisms. An equation was developed to describe the maximum height of the inside soil heave. Prediction of the total penetration resistance was described with a simplified flow mechanism around stiffened caisson based on the observed LDFE results.

This paper presents semianalytical solutions to the consolidation of drainage well foundations in unsaturated soils with radial semipermeable drainage boundary subjected to time-dependent loading, and radial boundary condition is employed to illustrate the smear effect. First, the governing equations of excess pore-air and pore-water pressures are transformed into equivalent partial differential equations. Afterwards, the final semianalytical solutions of the equations based on the free strain assumption are obtained by introducing the Bessel functions and Laplace transform techniques. The inverse Laplace transform is performed to derive the solutions in the time domain by means of Crump's method. Furthermore, the solutions are verified to be reliable by the regressive solutions and the numerical solutions by finite difference method (FDM). Finally, instantaneous loading, ramp loading, exponential loading, and sinusoidal loading are adopted to illustrate the changing regularity of excess pore-air and pore-water pressures against the ratios of air-water permeability, radial semipermeability coefficient parameters, and loading parameters.

Long-term stability evaluation of unsaturated earth structures has always been one of the most important issues in geotechnical engineering. Most available methods are appropriate for calculating the maximum loads that the structures can resist when the hydraulic state is fixed, and the external loads are monotonically increased. In practical engineering, however, the hydraulic condition is ever changing, and so are the matric suction and the shearing strength of unsaturated soils. In this situation, the obtained minimized collapse loads can no longer be used as reference for the design criterion, which may greatly overestimate the stability of the structures. Classical shakedown analysis is a more appropriate method, which can only consider the variation of the loads but not the variation of hydraulic states. This paper presents a novel formulation for shakedown analysis of unsaturated soils considering both the variation of external loads and the variation of the shearing strength caused by drying–wetting cycles. By using the suction stress-based effective stress of unsaturated soils, the three-phased mixture is dealt with as a single-phased material. The suction-stress equivalent forces are established, and the variation of the hydraulic state is dealt with as the variation of equivalent forces. Numerical formulations are then developed by the combination of the finite-element method and the second-order cone programming. Some shakedown problems are solved, and the effect of hydraulic state variation on the shakedown limits of foundations, pavements, and slopes is studied in detail. It is shown that the neglection of moisture content variation would greatly overestimate the safety of earth structures, and the produced errors become more significant with the increase of the suction-stress increment and the decrease of the shearing strength. The shakedown limit reaches the smallest when both external loads and suction stress are varying. When the variation of equivalent forces is complicated, the loading domain can be approximated by a polyhedron using a uniform distribution of sampling points, and the shakedown factor of safety converges to the true value with the increase of the number of sampling points. Shakedown analysis is necessary in engineering designs when several wetting and drying cycles happen.

Rankine pressure involves the special case of active earth pressure and merely considers the influence of the internal friction angle; however, the analytical solution for the general case involving a rough retaining wall, inclined boundary, and soil dilatation effects has not been investigated to date. This study developed a new slip line theory that considered the dilatation effect and then derived a general analytical solution, which considered the internal friction angle, dilatation angle, interface friction angle, and inclination angle of the boundary. The sliding surface and pressure coefficients were discussed in terms of the numerical method of slip line theory. The analytical solutions of the pressure coefficients related to the surcharge and cohesion were found to be identical to the numerical results. When one of the interface friction angles and the inclination angle did not equal zero, the total earth pressure could not be simply expressed as the linear superposition of the three terms like the Rankine expression, and the total result was related to the ratio $(q+c\cot \phi )/\gamma$. When producing the earth pressure, this coupling effect between the surcharge, cohesion, and weight displayed regularity. The correction coefficient of the analytical solution for the pressure coefficient due to the weight was introduced and determined from the results of the numerical method, and a semianalytical solution was provided.

Although the influence of gradation on soil properties has been recognized, the grain sizes have not yet been fully considered in maximum dry density (MDD) evaluation and prediction. This study explores the impacts of full grain sizes on the MDD and evaluates MDDs through different particle size distribution (PSD) curves of gravelly soils. First, full grain sizes, d₁₀–d_100, were extracted from 90 gravelly soil samples and employed as input parameters to develop the neural model for MDD, by using genetic algorithm (GA) to optimize the back-propagation (BP) neural network. A mean impact value (MIV) method was then proposed to quantify the impact of each grain size, followed by the vibrating compaction tests for 22 artificially designated gravelly soil specimens to verify the model and evaluate the MDDs based on grain sizes. The model analysis and verification tests agreed with each other and clearly showed the intrinsic dependence of grain sizes on MDD for gravelly soils. As revealed by MIV analysis, d₅₀–d₁₀₀ and d₁₀–d₄₀ displayed positive and negative impact to MDD during compaction, behaving as the relatively coarse and fine grain sizes, respectively. Additionally, the relative impact weight showed that d₁₀₀ tends to have the largest impact to MDD, and high-sensitivity (HS), medium sensitivity (MS), and low sensitivity (LS) could be proposed to distinguish these grain sizes. As the MDD was found to correspond exactly to the unique soil gradation, the full grain sizes should be employed to precisely predict and correctly evaluate the MDD of gravelly soils.

In this study, the pertinence of a broken-back retaining wall with bilinear backface in mitigating the effect of earthquake is demonstrated using the method of stress characteristics coupled with the pseudodynamic approach. Unlike the available studies reported in the literature considering the limit equilibrium or the limit analysis method, a priori failure mechanism is not assumed in this analysis, and the failure mechanism automatically gets evolved from the solution of stress characteristic equations. The versatility of the solution procedure is explored with the available seismic methods such as pseudostatic, original pseudodynamic, and modified pseudodynamic approaches. The effect of various parameters such as inclination and roughness of the wall, angle of internal friction of the backfill soil, damping of the soil, and phase difference of seismic waves on the active thrust is determined in the analysis. The stability analysis of the wall is performed using the classical Newmark's sliding block approach. The present results are compared with the available data reported in the literature. The seismic stability factors are found to be critical while considering the dynamic properties of the soil and the wall. The efficacy of employing the broken-back geometry over the conventional vertical retaining wall is presented for different wall configurations.

This paper examines the influences of the size ratio and fines content on Young's modulus and the shear modulus of binary mixtures using the discrete element method. The moduli were gained by numerical simulations of drained triaxial compression tests. The contribution of each contact type is quantified, and the results indicate that the moduli are controlled by the combined action of various contact types. The analysis of microscopic characteristics shows that the moduli rely on the modified void ratio and 2/3 power of the modified volume-weighted coordination number. Additionally, a good relationship among the normalized modulus, the volume-weighted coordination number, and the peak friction angle is found.

Earthquakes have been found to seriously threaten the structure of tunnels. To study the seismic performance of a composite lining embedded in a saturated poroelastic half space under an incident P wave, an analytical model is established based on Biot theory, and the solutions are obtained utilizing the wave function expansion method. The dynamic stress concentration factor (DSCF) is introduced to describe the dynamic stress state in the composite lining. The dynamic stress of the composite lining is compared with that of a single lining, indicating that the composite lining can reduce the lining dynamic stress significantly. Subsequently, the influence of the dimensionless input frequency, incident angle, thickness, and stiffness and the buried depth of the composite lining on the aseismic performance of the composite lining are discussed. The conclusions obtained in this study might provide a beneficial guideline for composite lining design in tunnel engineering.

The earthquake-induced rock avalanche in the Tangjia Valley was the most notable geological disaster triggered by the Lushan earthquake in 2013. In order to investigate the transport kinematics and depositional mechanism of this catastrophic landslide, a 2D discrete element model was developed and calibrated using field data. The model was then used to analyze the seismic response and mass transport process of a natural slope. The slope response to earthquake was numerically studied focusing on crack initiation, propagation, and coalescence within the rock mass. The mass movement and accumulation process were interpreted in terms of evolution of stress and solid fraction, kinematic behavior, and energy conversion. During the mass transport process, the slope was fragmented progressively due to intense shearing, allowing a basal layer of gradually fining solid particles to be generated with simultaneous occurrence of violent collisions, increase in particle kinematic activities, and the reduction of solid concentration. To further study this deformation process, fragment size distributions and fractal dimensions were described by Weibull distribution and power-law function, respectively. This statistical analysis reveals that dynamic disintegration continuously operates with the increasing runout distance. It is also found that the distribution of the fragment shapes becomes stable as the avalanche loses its momentum and deposition starts in the runout area. The proposed framework for the analysis of rock avalanches can be used to understand the physics of similar geological hazards.

Novel geomechanics concepts for seismic design satisfying the current performance-based seismic design (PBSD) requirements are presented. Issues related to soil conditions are explicitly addressed. To satisfy the underlying dynamics as realistically as possible, structures are represented by finite elements and the earthquake excitations are applied in time domain. PBSD is essentially a sophisticated risk-based design concept. To incorporate uncertainty in the seismic loading, the current design guidelines require the consideration of at least 11 design earthquake time histories. For wider acceptance, information on the seismic risk is extracted using multiple deterministic analyses. The proposed concept is showcased by estimating the underlying risk of a nine-story steel building designed by experts for several performance levels and different soil conditions. The basic intent of PBSD is to limit the probability of collapse to about 0.10. The study confirms that the building was well designed by the experts and the proposed method confirms this requirement. The authors believe that they proposed an alternative to simulation and the classical random vibration concept.

Understanding the strength and deformation response of hard and soft rocks under cyclic loading is very important for assessing fatigue in rock engineering structures. The effect of cyclic loading on rocks is different and more complex than that of monotonic loading. In this paper, the deformation and strength response of two mineralogically and microstructurally different rocks, sandstone and granodiorite, are investigated by conducting multistage uniaxial cyclic compression loading tests. It is shown that these two rocks behave differently under cyclic loading mainly because of their microstructures. The stress–strain hysteresis loops of sandstone samples showed three phases of development, while there were two phases for granodiorite samples. The fatigue strength threshold of granodiorite as hard rock is shown to be less than that of sandstone as soft rock. Residual lateral strain develops faster than residual axial strain during the cyclic stages. Axial and lateral strains after each step of loading, as well as residual strain, showed an increasing trend with maximum stress levels and loading amplitude. We discuss how rock damage develops in a rapid manner in lower loading frequencies and find that rock damage propagation can be assessed by ultrasonic measurement. The failure modes of the rock samples were also evaluated. We found that the damage mechanism of rocks under cyclic loading is highly dependent on loading frequency. In addition, the failure modes of the two rock types under cyclic loading differ not only from those under the monotonic conditions but also from those under different loading conditions. This study contributes to a deeper understanding of the deformation response and damage evolution of hard rocks and soft rocks under fatigue processes.

In water-rich rock masses from underground excavations, the flow pressure and confining pressure significantly affect the seepage properties of the fractured rock induced by complex stress. To understand the seepage mechanism of fractured rocks under stress, seepage tests on fractured granite and slate specimens after triaxial compression were carried out under confining pressures from 1 to 10 MPa by using the self-developed temperature–stress–seepage coupling test system. The evolution from linear to nonlinear seepage process is comprehensively investigated by changing the seepage pressures gradient. The flow rate increases when increasing the seepage pressure gradient and decreases when increasing the confining pressure. To illustrate the influence of fracture morphology on the physical mechanism of seepage, fracture surfaces of rock specimens after seepage tests were scanned by a three-dimensional structural optical scanner. The fracture surface morphology of different rock types influences the seepage mechanism in different ways. Under the same seepage condition, the first-order waviness has a greater influence on reducing the critical Reynolds number. The larger the waviness, the more easily the nonlinear seepage occurs in the rock fractures. The relationship between the seepage pressure gradient and the flow rate has been well described by the Forchheimer equation, and the seepage process can be divided into Darcy flow and nonlinear flow. Under the same seepage pressure gradient, the Reynolds number decreases as the confining pressure increases. The nonlinear seepage feature tends to be more evident when increasing the confining pressure. The nonlinear factor E = 0.1 was determined to be the key point to solve the critical Reynolds number and the threshold for nonlinear flow. The Euler numbers of granite fractures are two orders of magnitude larger than that of slate fractures. This is because the first-order waviness on granite fractures fluctuates more significantly than those of slate fractures, leading to a large local resistance loss.

In order to accurately and efficiently simulate the dynamic processes of coupled phenomena with viscoelastic, continuous and discontinuous deformations, a three-dimensional (3D) numerical manifold method combining Maxwell's viscoelasticity (3D-VisNMM) is proposed and implemented in this study. First, the matrix formulas of 3D-VisNMM are derived, and then its technique flowchart is presented. Second, four viscoelastic models, which represent creep characteristics, stress relaxation features, stress accumulation, and frictional deceleration, respectively, are used to verify the feasibility of 3D-VisNMM. The creep model shows that the simulated deformation at each time step is highly consistent with the analytical solution. The stress relaxation model shows that the accuracy of simulated stress mainly depends on the time step, that is, the range of the Relative Standard Deviation (RSD) is 0.3%–4.8%, which corresponds to a time length of 0.1–2.0 years. The gravity-driven stress accumulation model shows that the RSD between the simulated results and analytical solutions is less than 0.004%. The frictional deceleration simulation shows that the RSD of cumulative displacements and accelerations are less than 0.65% and 2.4%, respectively. All these numerical simulations show that 3D-VisNMM is suitable for analyzing viscoelastic deformations, stress relaxation, and frictional sliding issues in multitemporal scale (second–century) and multispatial scale (meter–hundred kilometers). Therefore, 3D-VisNMM has a good application prospect in Geoscience research.

A new instability criterion based on the critical slope concept and the double strength reduction is proposed to evaluate the stability of slopes. In this method, the critical slope contour is determined by the slip-line field theory with the reduced cohesion and the internal friction angle, and the slope reaches the limit equilibrium state when it intersects with the critical slope contour at the toe of the slope. The proposed method is validated against a published case and compared with the traditional instability criterion. In addition, the calculation results regarding four slope cases revealed that the reduction ratio of soil strength derived from the proposed method is more reasonable, and the comprehensive safety factor is equal to the polar diameter method. Thus, the proposed method can be adopted to quantify the instability criterion.

This paper proposes an empirical solution to calculate the average ultimate cavity wall pressure (UCWP) of cavity expansion in undrained clay under anisotropic stress through large deformation finite element analysis using a coupled Eulerian–Lagrangian technique. The soil around the cylindrical cavity is assumed to behave as the elastic–perfectly plastic material, as the description of Tresca yield criterion. The parametric study is conducted considering the influence of shear modulus, shear strength, initial stress, and anisotropy coefficient. Then an empirical equation of the average UCWP is proposed. This empirical solution and relevant analysis complement the study of cylindrical cavity expansion and reveal the mechanism of the cavity expansion under anisotropic stress.

The deformation and degradation of fouled ballast have been examined by large-scale triaxial tests and discrete element modeling (DEM) to understand how clay fouling changes the shear strength and micromechanical aspects of ballast. Particle shape analysis using 3D aggregate imaging and a laser scanner is introduced to construct more realistic polyhedral discrete elements that will represent natural ballast particles. Shear stress-strain and volumetric changes of fresh and clay-fouled ballast are analyzed. Micromechanical analysis of the fouled ballast is carried out and the effects of fines are quantified by considering the changes of ballast breakage, particle connectivity number C_n, and the associated distribution of contact forces that could not be measured experimentally. These findings enable a more insightful understanding of the load-deformation of fouled ballast from a micromechanical perspective.

The stability of long horseshoe tunnels in cohesive-frictional soils is examined by using lower bound finite element limit analysis. Its stability is assessed by determining the magnitude of uniform internal normal pressure required to be applied along the tunnel peripheral face. If the pressure required to be applied to the tunnel peripheral face at a particular soil cover depth and soil condition is compressive in nature, then it indicates that the tunnel is unstable without the lining pressure at that particular condition. The analysis has been done for different combinations of (i) soil cover depth (H), (ii) ratio of tunnel height to width (h/B), (iii) peak soil friction angle ϕ, and (iv) γB/c where c refers to soil cohesion, γ is soil unit weight, and B is the tunnel width. The results are presented here in terms of normalized compressive internal pressure (σ_t/c) for both smooth and rough tunnel boundary conditions. The magnitude of σ_t/c appeared to (a) increase with an increase in γB/c, h/B, and H/B and (b) decrease with an increase in ϕ and roughness condition of the tunnel boundary. The results are presented in the form of dimensionless charts.

The rise in failure of retaining walls subjected to dynamic loads is of increasing concern in earthquake-prone areas. The purpose of this study is to establish a closed-form solution for seismic active thrust and its distribution on a retaining wall subjected to surcharge stresses. The proposed method considers dynamic properties of the backfill soil to capture more realistic behavior. An upward propagating SH wave obeys boundary constraints, owing to surcharge acting on the surface of the backfill. Both the incident wave and the wave reflected from the surface of the backfill are considered in the analysis. An amplified SH wave is considered to estimate both inertial force due to surcharge and inertial force due to retained soil mass. Results obtained from limit equilibrium analysis are compared with those obtained by performing numerical analysis using finite-element modeling. It is observed that the frequency of the seismic wave plays an important role in estimating the seismic coefficient of earth pressure for different surcharge magnitudes. The study reveals that though the amplification of the wave is not much affected by the magnitude of the surcharge, consideration of the amplified wave when estimating the inertial force due to surcharge influences the total seismic active thrust. Obtained results are in good agreement with the well-established pseudostatic method. An attempt is made to study the effect of strain-dependent dynamic soil properties on seismic lateral coefficient for varying surcharge coefficients. This study definitively answers the question regarding the behavior of retaining wall with surcharge subjected to seismic loading that considers wave propagation.

During the transient phase of liquefaction, i.e., from the onset of liquefaction to the stage of full liquefaction of soil, intrinsic properties of a soil–pile–structure system change causing a significant modification of the transient forces experienced by the pile foundation. However, adequate estimation of transient forces of pile foundation in liquefiable soils for different strong ground motions is not well established. Three-dimensional fully coupled dynamic analyses have been carried out using software OpenSees for piles embedded in single and two-layer soil profiles. Variable permeability of saturated sand has been implemented for higher accuracy in the simulation of cyclic behavior of sand during liquefaction. It was observed that maximum forces in the pile section occur in the transient phase with excess pore pressure ratio in the range of 0.50–0.75 for uniform soil and 0.60–0.90 for layered soil profiles for earthquake motions considered. This study presents the maximum transient forces expected in the pile section in nondimensional forms for a wide range of strong motion parameters, for example, predominant frequency, peak ground acceleration, bracketed duration, and Arias intensity.

In this technical note, the seismic bearing capacity coefficients of shallow foundations placed on soft ground reinforced by stone columns are evaluated based on the upper-bound theorem of limit analysis. A kinematically admissible failure mechanism is developed that permits the evaluation of the bearing capacity under various values of the horizontal seismic coefficients. A series of design charts covering a wide range of parameters are presented to provide guidelines for the preliminary design of groups of stone columns in seismically active zones. The results from previous studies and an upper-bound limit-state plasticity failure discretization scheme [employing discontinuity layout optimization (DLO)] are used to validate the accuracy of the developed formula.

Earthquake-induced hydrodynamic pressure on the ocean floor is a key factor in evaluating the surface disturbance and dynamic response of the seabed under the action of a submarine earthquake. An analytical study considering the compressibility of seawater was carried out to obtain the closed-form solution for the hydrodynamic pressure, which depends on water depth, excitation frequency, and seabed characteristics. The commonly used approximate expression for the hydrodynamic pressure, which neglects the compressibility of seawater and is associated with the dynamic displacement of the seabed surface, is presented and compared with the analytical solution. The results reveal that the formulation neglecting the compressibility of overlying seawater could underestimate the hydrodynamic pressure at the ocean bottom and the induced dynamic responses in a poroelastic seabed. Finally, a modified formula for the seismic-induced hydrodynamic pressure at the ocean bottom interface, which is able to consider the compressibility of seawater, is proposed by incorporating the nondimensionalized frequency.