International Journal of Geomechanics

Methane hydrate-bearing soils (MHBS) are natural soil deposits that contain methane hydrate (MH) in the pores and have attracted a huge amount of attention as alternative energy to study mechanical properties for realizing large-scale commercial extraction. Especially, MHBS respond to applied loads under complex stress conditions, that is, the effect of the intermediate stress ratio on mechanical characteristics of MHBS. The effect of different values of intermediate stress ratios on the geomechanical responses of pore-filling MHBS was analyzed using the distinct element method (DEM). MH clusters are cemented together as agglomerates of spheres, which fill into the voids of the soil specimen according to the MH saturation. Then, the numerical pore-filling MHBS experimented with different loading paths of the true triaxial tests. Finally, the effects of the intermediate stress ratio on the mechanical characteristics of pore-filling MHBS were analyzed from two aspects, that is, macromechanical responses and micromechanical responses. The results showed that there were correlation analyses between the variations in the strong fabric and principal stresses. The friction angle increased with the intermediate stress ratio until it reached a peak value, and decreased thereafter. The Lade–Duncan criterion is approximately suitable to describe the three-dimensional strength of MHBS.

The design of slope-stabilizing piles is still an open issue for civil engineers, owing to the high number of variables to be determined in the design process and to the complexity of soil–structure interaction problems. In this paper, in the simplified case of subhorizontal cohesive soil strata, analytical solutions are proposed for the maximum available stabilizing action for a pile, also considering the possible presence of an anchor at the pile’s head, and thus extending some results already available in literature. Within the framework of an ultimate limit state approach, the influence of soil mechanical properties, of pile characteristics, and of the anchor strength are investigated, and some dimensionless abaci are analytically derived. The solutions demonstrate a marked coupling effect between tensile anchor strength and pile-bending resistance, and an explicit optimization strategy for a safe and effective dimensioning is provided. The results can be profitably employed in the most common limit equilibrium methods for slope stability analysis.

This paper presents a three-dimensional discrete numerical analysis associated with the interaction of geogrid and surrounding soils in geogrid-reinforced sand foundations under strip footing. After validating the numerical simulations with experimental results, the model was then employed to examine the deformation behaviors, contact force network, energy dissipation mechanism, and response of the geogrid. Additional analysis was also carried out to understand the effect of geogrid layout parameters on the bearing capacity of foundations and progressive failure of reinforcements. The results showed that the inclusion of geogrid layers spaced at 0.25B (B = footing width) inhibits the horizontal displacement of soils in the reinforced zone, whereas facilitates the displacement field in the underlying unreinforced zone and consequently results in an upward tensile failure of reinforcements. The progressive failure of reinforcements induces fluctuations of the loading–displacement curve in the postpeak regime. Punching shear failure initially develops in the reinforced zone in terms of force chains developing directly beneath the footing. With footing settlement increasing, the failure mode is characterized by a punching failure with a diffusion angle developing in the reinforced zone, followed by a general shear failure in the underlying unreinforced zone. Furthermore, the progressive failure of geogrid layers is associated with reinforcement spacing and number of reinforcement layers, rather than reinforcement length. A larger reinforcement spacing and a higher number of reinforcement layers tend to induce a downward fracture failure.

Compacted scaly clays are complex geomaterials widely used for the realization of dam cores and waste dump liners. This research aims to investigate the swelling/shrinkage behavior of these geomaterials subjected in an oedometric cell to complex hydromechanical stress paths, including different sequences of cyclic variations of suction and stress. Microstructure investigations, based on scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) techniques, highlighted the microstructural characteristics of the material, which are the distinctive microfabric features (particles assemblages and scales) and the double-porosity networks, where micro- and macropores coexist. Moreover, the MIP technique, applied to the tested oedometric specimens, provided significant elements supporting the microscale interpretation of the observed behavior on the basis of mechanical interaction between the different levels of microstructural arrangements. In all the cases analyzed, the suction cycles induce a microstructural rearrangement in the macropore domain, enhancing the stability of the fabric of the compacted clay. Suction-controlled oedometric test results were modeled with an elastoplastic constitutive model, which considers the role of a double structure in the behavior of unsaturated soils. The results obtained highlight the mutual influence between wetting/drying cycles and loading/unloading paths on the volumetric behavior of the geomaterial.

Use of pervious concrete piles is a ground improvement technique to improve soft soil’s load-bearing capacity by accelerating radial consolidation. With improved stiffness, pervious concrete piles perform well even under the low lateral confining pressure offered by soft clay. Improved stiffness and optimum permeability of pervious concrete piles make them, along with encased stone columns, a thriving solution to improve the soft clay deposit under embankments and other constructions. This study focused on determining the consolidation behavior of soil with pervious concrete piles of improved permeability. To facilitate the study’s objective, an innovative dented sheet liner was introduced in the casting of pervious concrete piles to improve permeability along the surfaces. PLAXIS-3D studied the effect of improved permeability by the liner in settlement performance and pore pressure dissipation. Performance of the pervious concrete pile cast with a liner was compared with a conventional pervious concrete pile and granular column. The study considered parameters such as diameter, length, and spacing. A numerical analysis revealed that improved permeability using a dented sheet liner accelerated the radial consolidation without affecting load-carrying capacity than other drains while maintaining the strength of the pervious concrete cast.

Cracks are one of the major characteristics of soil structure failure. Successfully performed numerical simulation of the soil crack evolution process is conducive to the prediction of potential dangers. In recent years, crack evolution simulation has been greatly facilitated in the field of fracture mechanics by the development of the extended finite-element method (XFEM). However, it is rarely used to simulate crack evolution in earth structures, because in most cases soil cannot be regarded as a quasi-brittle material. Based on the characteristics of stress concentration and redistribution at the tip of a soil crack revealed by numerical tests, this paper proposes a discriminating method for crack propagation that can reflect the influence of the stress field at the soil crack tip on the crack propagation direction, which is then coded to an XFEM program. Compared with existing methods, this new method is found to be more accurate and effective.

The infiltration of slurry in granular media plays an important role in face stability during slurry shield tunneling. This study investigates the effect of slurry viscosity in Fujian standard sand through a series of column tests combined with microstructural investigation, which remains unclear. The viscosity of slurry covers a wide range, from 1.8 to 2,248 mPa·s. Slurry particles in the low-viscosity test (1.8 mPa·s) fail to form an impermeable cake due to the loose stacking of slurry particles retained in sand voids, corresponding to a slight water pressure difference and relatively large permeability. For the high-viscosity test (2,248 mPa·s), an impermeable cake forms at a shallow depth; however, this internal cake is vulnerable to be disturbed and damaged due to its shallow thickness. Ultimately, one recommended viscosity, 56 mPa·s, is identified as a transition state with two-stage intact clogging, exhibiting an effective infiltration depth and intact internal cake that forms simultaneously. Experimental observations show a negative water pressure difference in the high-viscosity test, attributable to the siphonic principle. Furthermore, a measurement of slurry samples and solutes using the material observation apparatus could provide the microstructure evidence to interpret the effect of slurry viscosity in infiltration clogging. This study offers a reliable reference for interpreting the effect of viscosity on slurry clogging in infiltration performance.

A similar theoretical approach is generally used to estimate the end-bearing capacity of straight and screw piles. However, under similar ground conditions (stress level and bearing-capacity factor) and pile tip area after the pile is installed, the end-bearing capacity of the screw pile is less than the straight pile. In this study, the experimental tests were modeled in a three-dimensional (3D) finite-element code to better understand the pressure distribution and mobilized shear strength under straight and screw piles embedded in similar ground conditions. Moreover, the effect of helix position on the pile bearing capacity and pressure beneath the helix and shaft of the screw pile was also investigated. A helix-to-shaft diameter ratio (D_h/D_SS) of 2.8 was used. A good agreement between experimental and numerical results was found. The results indicated that the pressure distribution under the screw pile with a thick helix (non-deformed helix) and straight pile are similar when the helix is positioned (d_h) at the pile tip (d_h = 0). As the helix is moved further away from the pile tip (d_h > 0), the pressure under the helix gradually decreases, while the pressure under the shaft increases and then decreases within a certain d_h/D_h. The mobilized shear strength contribution of the helix decreased with the increase in helix position-to-helix diameter ratio (d_h/D_h). Moreover, when d_h/D_h ≥ 1.5, both central shaft and helix behaved independently, and their contribution in mobilized shear strength cannot be considered as a group. Regarding the effect of the helix position on the shaft pressure, when d_h/D_h < 1.5, the ratio of screw pile to straight pile end-bearing capacity decreases almost linearly with the increase in d_h/D_h. A modified equation is proposed that includes the two factors—helix position and shape (helix which differentiates screw pile shape from the straight pile)—to estimate the end-bearing capacity of the strong helix screw pile.

Particle breakage and particle shape are two prominent characteristics of carbonate sand. In this study, a series of drained shearing tests with different axial strains and confining pressures were performed to investigate particle-breakage development and particle-shape evolution under triaxial loading conditions. In addition, the correlations between particle-breakage evolution and particle-shape evolution and among the particle-shape parameters from both the specimen-scale morphology of all particles in a specimen and the grain-scale morphology of 3,200 grains in a specimen were studied. The test results showed that particle breakage develops with increasing axial strain and confining pressure. The relative breakage index has very strong correlations with the representative overall particle shape and the representative particle-shape parameters except the representative convexity. Moderate or high intercorrelations were observed for the particle-shape parameters of selected grains except convexity. Generally, convexity has the poorest relationship with the other three particle-shape parameters.

This paper presents semianalytical solutions of one-dimensional (1D) consolidation for unsaturated soils with depth-dependent vertical stress induced by multistage load. Based on the 1D consolidation theory of unsaturated soils proposed by Fredlund and Hasan, semianalytical solutions of excess pore pressures and settlement subjected to depth-dependent stress in a Laplace domain are derived by adopting Laplace transform and differential operator method. Then, the analytical solutions in time domain are obtained by Crump’s method, and corresponding computing programs are compiled. The correctness of obtained solutions has been validated by comparing the current solutions in this paper with those under only time-dependent load in the existing paper. Finally, considering the two-stage load scheme, parametric studies are carried out to discuss the 1D consolidation properties for unsaturated ground under the depth-dependent stress.

In the practice of reclamation engineering, surcharge loading is gradually applied to preconsolidate soft clayed soil. The in situ drainage boundaries are usually not perfect and can be in a state between fully impermeable and permeable with time. Traditional consolidation theories for homogenous soil with drainage boundaries under instantaneous loading thus cannot provide accurate prediction of the consolidation behavior. This paper extends the one-dimensional consolidation solution by considering the multilayered inhomogeneity of soil, general time-dependent loading and continuous drainage boundaries. Laplace transform and a novel transfer matrix formulation developed in this paper are used to solve the problem. Analytical solutions of excess pore water pressure and average degree of consolidation are derived and expressed in term of inverse Laplace transform. Numerical results in the physical domain are obtained with the aid of Crump’s algorithm. The present solutions are verified by comparing with the results in the literatures for some special cases, including multilayered soil and two-layered soils with continuous drainage boundaries under instantaneous loading. For the limiting case of homogenous soil, the present solution can analytically reduce to closed-form Terzaghi’s solution. Parametric studies are performed using the new solutions to investigate the consolidation behavior of a four-layered soil. It is shown that the drainage boundary condition, loading path, and loading rate can have a considerable effect on the excess pore water pressure and average degree of consolidation.

The bearing capacity of a shallow strip footing is investigated by a pseudodynamic method under earthquake conditions. A nonsymmetrical multiblock mechanism is herein adopted to describe the uplift failure of the foundations based on the kinematic theorem of limit analysis. This nonsymmetrical mechanism comprises a series of rigid triangular blocks that translate into the failure area. The seismic load, varying with time and space, is represented by a pseudodynamic method that considers the dynamic properties of earthquake waves. A slice method is proposed to adapt the variation in inertial force with time and depth for the convenience of calculating the earthquake-induced work rate. Then, equating the external work rate and the internal dissipation rate, the rigorous upper-bound solution of the seismic bearing capacity factors, which will be optimized by the sequential quadratic programming (SQP) in the MATLAB toolbox for searching for the optimal value, is explicitly derived. Comparisons between the present solution and previous works are made to validate the rationality and accuracy of the proposed methodology. A specific parametric analysis is conducted to reveal the influence of dynamic parameters on the bearing capacity of the strip footing. Numerical results are provided graphically as well as in the tabular form for reference in footing design.

The Loess Plateau in Northwest China is located in a seismic area. Therefore, the high-filled cut-and-cover tunnels (HFCCTs) in this area are subjected to high earthquake risk. The load reduction measure of laying an expanded polystyrene (EPS) board on top of the Cut-and-Cover Tunnels (CCTs) can effectively reduce the earth pressure around the HFCCTs and lower the risk of potential failure of structures. However, due to the frequent disastrous earthquake events in the Loess Plateau area in Northwest China and the high dynamic sensitivity of the backfill soil, the seismic load may disturb the already stable backfill soil. Also, the stability of the soil arching effect and earth pressure due to load reduction under the seismic load is unknown, which may adversely affect the CCTs and, therefore, this unknown factor needs to be considered carefully in HFCCT design. Accordingly, the finite difference program, FLAC3D, was employed in this study to conduct numerical analyses of the earth pressure distribution around the CCTs and the evolution of the soil arching effect in the backfill when subjected to the seismic load. Parametric studies of seismic waves were also conducted to investigate two influential factors: the types of seismic waves and the peak ground acceleration of earthquakes. The results showed that the earth pressure around the CCTs and the soil arch evolution in the backfill were significantly affected by the seismic load. Therefore, the seismic load must be taken into account for HFCCT analysis and design in earthquake zones.

An increasing number of concrete faces rockfill dams (CFRDs) are being built on deep alluvium foundations. Understanding the behavior of CFRDs that are built on alluvial foundations is critical to the performance assessment and design optimization of these dams. This paper aims to quantitatively study the influence of alluvial foundations on CFRD behavior and discusses the corresponding treatment measures. Four parameters are proposed to describe the distribution characteristics of alluvium foundations. The parameters are related to the mechanical properties of an alluvium foundation, which have practical physical meaning. A series of numerical calculations are performed on the behavior of CFRDs with different alluvium characterization parameters based on a case history. The influence of an alluvium foundation distribution on CFRD behavior is quantitatively analyzed according to the numerical calculations and measured data from case histories. Corresponding treatment measures or suggestions for the dam or foundation are discussed. The findings could offer reliable insights into CFRD behavior on alluvium foundations and provide an engineering analogy or reference for the planning, design, and construction of CFRDs.

This paper presents a prediction model for the shear strength of fiber-reinforced soil. A series of triaxial compression tests were first conducted to investigate the influences of fiber content and fiber length on the shear strength behavior of fiber-reinforced soil under different confining pressures. Experimental results on the stress–strain relationship, shear strength improvement ratio, shear strength parameters, and reinforcement mechanism are presented and discussed. Results indicate that the shear strength of fiber-reinforced soil increases significantly with increasing fiber content, but there exists an optimal value for strength improvement. The fiber content and fiber length have little influence on the friction angle of fiber-reinforced soil, while the apparent cohesion increases significantly with increasing fiber content and fiber length. Based on the experimental data, a prediction model was proposed for the shear strength of fiber-reinforced soil using the concepts of equivalent apparent cohesion and equivalent normal stress. The model can capture the decrease in shear strength improvement effect due to excessive fibers and can predict the shear strength of fiber-reinforced soil with good accuracy using fiber parameters and shear strength parameters of unreinforced soil.

This paper presents an improvement on a previous model for predicting the Marsh funnel (MF) test that is used in slurry shield tunneling for evaluating the rheological properties of bentonite slurries. The improvement focuses on the prediction of the dynamic part for fluids with small MF times. The velocity profile of the Herschel–Bulkley fluid in a laminar pipe flow condition is first investigated and a correction factor is introduced in the improved model. Comparisons of results from experiments and calculations with the previous model confirm the improved performance over the existing model. The rheological parameters obtained from the improved model show good resemblance to those obtained from a laboratory viscometer. The work also provides a reference to similar applications such as fluid transportation through pipelines where dynamic pressure dominates and therefore should be correctly predicted considering its velocity profile in a laminar condition.

This study proposed an effective approach to accurately evaluate the three-dimensional (3D) seismic bearing capacity of heterogeneous and anisotropic slopes in the framework of the upper-bound limit analysis theorem. An improved discretized horn mechanism was first developed so that the properties of heterogeneous and anisotropic soils could be involved in the slope stability analysis. To incorporate the impact of seismic forces, the modified pseudo dynamic approach was adopted, which ensured that the complete time-history of the seismic-induced ground movement, the soil-damping properties, and the amplification effect could be considered in this study. The seismic bearing capacity of slopes was then calculated by using a method that integrated the upper-bound limit analysis theorem and the modified pseudo dynamic approach. The proposed method was validated by comparisons with previous analytical solutions for some available cases, showing that the proposed method is an effective approach to determine the 3D seismic bearing capacity of heterogeneous and anisotropic slopes. The effects of model parameters on the ultimate bearing capacity and the critical failure surface are then presented. Finally, the influence of pore–water pressure on the seismic slope stability is discussed.

This paper examines static liquefaction phenomena in sand–clay mixtures from both experimental and theoretical perspectives. Consolidated undrained triaxial tests (CU tests) are implemented on a mixture of sand and clay to study the effects of initial relative density, confining pressure, and clay content on static liquefaction responses. By using the equivalent granular state parameter, a state-dependent hardening plasticity model is proposed to reproduce mechanical responses, as well as to replicate the observed static liquefaction phenomenon. In accordance with the second-order work theory, the criteria for predicting the potential instability and static liquefaction of sand–clay mixtures are obtained. The analyses show that (1) static liquefaction is prone to be promoted by low initial relative density and confining pressure; (2) even a small amount of clay particles can significantly increase the liquefaction susceptibility in loose sand–clay mixtures; (3) the proposed constitutive model can provide a satisfactory match between the test data and the simulations; and (4) even when the state of the soil is potentially unstable, soils can still remain stable unless second-order work vanishes, which indicates the inception of static liquefaction.

In recent years, accurate determination of the effective stress factor has been found to be instrumental for classifying the types of pore water and defining the form of their contribution to the unsaturated soil strength. In this study, a series of laboratory experiments based on volumetric flask, indoor evaporation and low-field nuclear magnetic resonance (NMR) methods were conducted on Wuhan clay to determine the relationship between adsorbed water content and matrix suction, and hence the adsorbed water retention curve (AWRC). The capillary water retention curve (CWRC) is the curve derived by subtracting the AWRC from the soil water characteristic curve (SWCC). This CWRC is then utilized to obtain correlation between the degree of saturation of capillary pores (S^cap) and the matrix suction. The effective stress factor was replaced with S^cap for determining the shear strength of Wuhan clay with three different dry densities. It was observed that the predicted values of shear strength obtained by NMR-based methods are more accurate than two other methods available in the literature. Furthermore, the accuracy of the method is not impacted by changes in dry density or confining pressure.

Most theoretical analysis for the assessment of the stability of soil slopes is commonly performed under completely dry or saturated and homogeneous conditions, the effect of suction and soil inhomogeneity are generally ignored in stability assessments. This paper presents an analytical framework to investigate the stability of three-dimensional (3D) inhomogeneous slopes in unsaturated soils under one-dimensional steady flow. Based on the kinematic limit analysis method, a 3D rotational failure mechanism is adopted, and three possible failure mechanisms of soil slopes (e.g., toe, face, and base failure) are considered. A closed-form solution for the factor of safety is derived by the energy balance equation, which takes the effects of the suction stress, effective unit weight, and inhomogeneity of soil simultaneously into account. To improve optimize efficiency, a genetic algorithm (GA), which has the advantages of high efficiency and good accuracy, is applied to search for the minimum of the factor of safety of the slope. This methodology is well validated through comparison with existing solutions and numerical simulation. Parameter analyses are performed to investigate the effects of different parameters on slope stability. The results of the present study indicate that the stability of the slope will be underestimated if the suction stress and the change in effective unit soil weight are not considered. The inhomogeneity of soil can reduce the stability of slopes.

Dip slopes are often encountered in deep-cut canyons and engineering projects. Such slopes, when they become unstable, commonly undergo bi-planar failure, and this mode of failure tends to produce the widest-ranging effects. In this work, a novel method is proposed for assessing the potential of a slope to undergo bi-planar failure based on a stress analysis at a key point on the sliding surface, namely, the point at which the two sections of the sliding surface are connected. Discrete-element simulations are first carried out to capture the essence of the penetration process of the bi-planar sliding surface based on displacement results, plastic failure, and principal stress development. Then, the key point on the sliding surface is skillfully selected according to the sliding surface penetration process, and the characteristics of the stress changes leading to slope failure are investigated using the stress analysis method. Subsequently, considering the stress states of this key point both in the overlying rock strata and in the intact rock at the toe of the slope, a novel method is proposed for assessing the stability of the dip slope and predicting the bi-planar failure surface formed. The stability of dip slopes was subsequently analyzed using both numerical and theoretical methods. The results obtained are highly consistent, confirming the feasibility and accuracy of the proposed method. The results also show that the bi-planar failure process is progressive and that the range of the failure is mainly located in the stress reduction zone. Moreover, the critical height of the dip slope remains approximately unchanged as the stratum thickness is changed. However, it decreases as the slope angle increases and increases linearly if the strength of either the rock or joints is increased. Additionally, if the joint strength is low, the dip slope undergoes buckling failure—increasing the joint strength, however, increases the likelihood of the occurrence of bi-planar failure. The proposed method offers a novel approach to assessing and designing dip slopes.

Equally spaced piles can be designed to ensure the stability of a slope with a desired safety factor or to restrain slow slope movements to prevent damage to existing structures. The piles are usually arranged in lines installed transversally to soil movements or in groups of limited extension in a plan according to their stabilizing or protective function. A numerical study has been performed to analyze the role of some design parameters in the efficiency of equally spaced piles, adopting two-dimensional (2D) and three-dimensional (3D) finite-difference (FD) models. Plane strain models have been used to study the soil arching mechanism and the associated stress transfer from the yielding soil to the stabilizing piles, while 3D numerical analyses have been performed to evaluate the efficiency of pile groups. The effect of varying pile spacing, pile embedded length, soil mechanical properties, and sloping ground conditions have been investigated for two-layer slopes assuming fixed or unconstrained piles. The outcomes of the parametric study made it possible to derive a simple analytical relationship to quantify the resisting contribution provided by the piles in an infinite slope. The paper shows that the proposed approach, even though limited to the ranges of the adopted parameters, can be used for a preliminary design of stabilizing piles to ensure the desired increase in the slope safety factor, as well as to achieve the desired reduction of downhill slope movements.

The evaluation of slope stability of a three-dimensional slope requires identifying the critical slip surface with the minimum factor of safety, which is a complex optimization problem. Failure to identify the critical slip surface can lead to unconservative conclusions about the stability of a slope. This paper proposes a novel 3D surface-altering optimization method, which iteratively alters the geometry of a 3D slip surface to find the critical slip surface representing the minimum factor of safety in a slope. The geometry of the slip surface is defined via nonuniform rational basis spline (NURBS) curves formed over a plan grid of control points. The proposed method includes a series of five subroutines that apply various forms of transformations to the control points. These subroutines include minimization problems, which determine the optimal transformation parameters for minimizing the obtained factor of safety of the resulting slip surfaces. Given that any geometrically defined slip surface can be approximated using an equivalent series of NURBS control points, the proposed method can be used in efforts to further reduce the global factor of safety first obtained via conventional search methods, such as those involving spherical or ellipsoidal slip surfaces. To demonstrate its effectiveness, the proposed method was applied to further optimize the critical ellipsoidal slip surfaces reported in some numerical examples. Comparing the results with those limited to ellipsoidal slip surfaces, the proposed method was consistently able to identify slip surfaces with significantly lower factors of safety. The postaltered slip surfaces also matched closely with finite element shear strength reduction results. As such, the proposed method is effective in searching for critical slip surfaces and can be used as a final step in the critical surface searching routine.

The combination of soil–cement (SC) columns and prefabricated vertical drains (PVDs) has indicated great success in improving ground stabilization in recent years; however, there is a lack of proper plane-strain numerical modeling to detail the role of PVDs in improving the performance of the SC column method. This study thus presents a numerical analysis of soft soil ground improved by the coupled PVD–SC column method based on a proposed equivalent plane-strain model considering the combined effects of PVDs and SC columns in the ground. The model is verified by applying it to a test embankment where long PVDs were installed in soft soil in combination with floating SC columns. To investigate the role of PVDs in the composite foundation, the numerical analysis is then conducted for two cases, with and without PVDs. The effects of discharge capacity of PVDs on the SC column behavior are also examined. The results show that the PVDs significantly improve performance of the composite foundation as they considerably reduce both postconstruction settlement and lateral displacement, while increasing the efficiency of soil arching and the bending moment capacity in SC columns. The numerical results obtained from the proposed model are in good agreement with the field data. The current study also shows that the discharge capacity of PVDs should be larger than 20 m³/year to enhance the positive influence of PVDs on the entire performance of the composite foundation.

Tsunamis cause scour and erosion on bearing grounds, resulting in ground instabilities that lead to damage to coastal structures. For example, with regard to the damage to breakwaters due to the tsunami from the Great East Japan Earthquake of 2011, scouring around these structures has been reported to be a cause of structural failure. However, the actual mechanism underlying such damage has not yet been clarified. Therefore, this study focuses on the scour and erosion of the seabed under a breakwater, specifically, as a result of bottom shear and seepage forces for different permeabilities of the rubble mound. In a flume channel experiment, seepage was investigated using point data measured on a pore water pressure sensor. To confirm the occurrence of spatial seepage in the mound and seabed, seepage analysis was conducted using finite-element analysis. The seepage was examined via a detailed comparison of experimental and numerical results. The results of the experiment show that scour and erosion of the seabed vary with respect to the permeability of the rubble mound. If the rubble mound is highly permeable, scouring of the seabed will occur because of seepage flow in the rubble mound. On the other hand, if the rubble mound is composed of a low-permeability material, seepage failure is the likely result. Seepage will also occur on the seabed following variations in water-level difference with a caisson. This suggests that the seepage will flow on the edge of the caisson on the outer harbor side and out to the edge of the caisson on the inner harbor side. Vertical motion of the seepage is generated on the seabed surface, and with increases in the permeability of the rubble mound, the upward hydraulic gradient in the inner harbor side of the caisson also increases. This study clarifies the relationship between normalized friction velocity and averaged hydraulic gradient using experimental data for erosion on a seabed surface under the rubble mound of a breakwater structure. As a result, a nondimensional index is proposed for the erosion initiation process on a seabed under a breakwater structure using the normal friction velocity and averaged hydraulic gradient.

Due to the limitation of cantilever wall in practice, an innovative retaining structure, named inclined framed retaining wall (IFRW), has been developed. The aim of this investigation is to analyze the factors influencing IFRW performance in clay and to determine the optimal IFRW layout. Validated finite-element models are used to evaluate the effect of the geometric parameters, including the angle of the inward inclined piles (θ_I), the angle of the outward inclined piles (θ_O), the length of the inward inclined piles (L_I), and the length of the outward inclined piles (L_O), on the maximum retaining structure displacement (δ_h,max). The results show that the IFRW utilizes the interface friction between the soil and the retaining wall. The horizontal component of the generated friction provides a resultant force pointing out of the excavation, which is similar to the effect of struts in propped excavation. Furthermore, the multivariate adaptive regression splines (MARS) procedure is adopted to find the optimal arrangement of the retaining wall system. The relative importance of each input parameter and their coupled interactions on the structure displacement are quantified.

This paper reports numerical studies into mechanical characteristics of tunnel stability in unsaturated soils using a modified upper bound discretization scheme, the discontinuity layout optimization (DLO) method. A modified approach, unsaturated DLO (UNSAT-DLO) was utilized to take into consideration the effect of suction stress on strength. A parametric study was carried out using the UNSAT-DLO approach for two simulated unsaturated soils. This was to examine the influence of soil capillarity on strength and failure mechanisms for five different scenarios of a circular shallow tunnel. The scenarios comprised various combinations of suction profile, water table height (H_w), effective internal friction angle, cohesion (considering soil fabric changes), shotcrete strength, and air entry suction, representing different soil types or soil hysteresis. The numerical results revealed a nonlinear relationship for the tunnel stability with suction. The tunnel stability for both simulated soils was seen first to rise with increasing suction and then to fall, owing to desaturation, slightly before and beyond the residual suction. The shear strength parameters, as well as the increase in shotcrete strength, owing to hydration, showed significant increase in the tunnel stability. Finally, an increase of about 6.63% in tunnel stability was obtained at ϕ′ = 30°, c′ = 0 kPa and H_w = −2 m when the air entry suction increased from 25 to 50 kPa. The modified UNSAT-DLO approach is, therefore, a promising tool that can be utilized to determine stability for various geotechnical applications at unsaturated conditions, such as tunnels, retaining walls, and slope stability problems.

For equivalent linear and nonlinear site response analysis, both shear modulus and damping ratio are critical input factors. The elastic modulus and damping ratio of saturated soft clay are usually determined using cyclic triaxial tests. However, the dynamic behaviors of saturated clay are affected by excess pore-water pressure induced under cyclic loading. Therefore, the evolutions of both elastic modulus and damping ratio, under cyclic triaxial tests with and without drainage, are the main focus of the investigation. Two types of cyclic triaxial tests were performed, in which the primary distinction is whether the excess pore-water pressure caused by the previous stage’s cyclic loading is released prior to the application of the next stage’s cyclic loading. The impacts of several parameters, such as effective confining pressure and excess pore-water pressure, were investigated. As the effective confining pressure increases, so does the maximum elastic modulus. Excess pore-water pressure has a significant effect on maximum elastic modulus. The maximum elastic modulus under the condition with drainage increases linearly with that obtained without drainage. Besides that, the variations of normalized elastic modulus with effective confining pressure are negligible under the condition without drainage, while the impact of effective confining pressure is more apparent in the condition of drainage. Nevertheless, the influence of effective confining pressure on the damping ratio can be ignored over the range of axial strain. The damping ratio without drainage is higher than that obtained under the condition with drainage. Based on that, the variation of normalized elastic modulus versus axial strain can be depicted by an empirical function, while the evolution of the damping ratio is represented by a hyperbolic model.

Unsaturated soil shear strength is a crucial and useful parameter for predicting geostructure stability, soil erosion, seasonal variation, and land management. Unsaturated shear strength measurement, however, is frequently costly, complex, and time-consuming. The main objective of this paper is to present a new generalized equation for the shear strength estimation of unsaturated soils. The proposed equation is derived from a micromechanical equilibrium condition considering the interaction of air, water, and solid phases. The particle contact area effect is taken into account in the proposed model, even though it is thought to be negligible in existing equations. In comparison with existing equations, the proposed one has the benefit of being able to capture the nonlinear influence of saturation degree and matric suction on unsaturated shear strength. The proposed equation is compared with several other existing equations as well as experimental data for four different soil types to verify its validity. The findings indicate that the proposed equation has a potential application in estimating unsaturated soil shear strength and that it outperforms existing equations. The stress state also has a substantial impact on the shear strength properties of unsaturated soils, which was extended to include in the proposed equation. The results reveal that the proposed equation is capable of accurately predicting the variation of the soil–water characteristic curve and unsaturated soil shear strength as a function of the stress state.

The yield stress and the coefficient of lateral earth pressure at rest, K₀, of soil are important parameters for geotechnical design. However, the effect of cementation on the values of yield stress and K₀ of artificially cemented sand along a K₀ path has not been fully studied, despite the common use of cement mixing for soil improvement. A series of consolidation tests of K₀ on artificially cemented sand has been conducted using a plane-strain apparatus. The test results show that the value of K₀ of cemented sand is very much affected by the amount of cementation; the lowest value of K₀ in a K₀ test corresponds to the yield stress provided by cementation. It is established in this study that the yield stress of cemented sand marks the start of a large amount of bond destruction. The value of K₀ reduces exponentially with the increase in cement content. One important practical implication is that the lateral earth pressure at rest can be reduced by introducing cementation to soil. This study also shows that Jaky’s equation is no longer applicable for estimating the value of K₀ of cemented sand, although it may still provide a rough estimate for clean sand. The value of K₀ of cemented sand can be estimated using a combination of Jaky’s equation for clean sand and Jaky’s equation for cement content.

The current study derives a closed-form analytical solution of buried pipeline subjected to underground blast load. The solution is derived considering Euler Bernoulli’s beam resting on viscoelastic foundation. In viscoelastic foundation, shear interactions between individual Winkler springs are considered. Soil pressure on the pipeline resulting from the self-weight of the soil above the buried pipeline is also incorporated in the present analysis. The finite sine–Fourier transform is employed to obtain the solution for the governing differential equation. The proposed formulation is validated with the results obtained from the past centrifuge model test, finite-element-based three-dimensional (3D) numerical analysis and simplified analytical study. Further, a parametric study is performed to obtain the impact of trinitrotoluene (TNT) charge weight, standoff distance, damping ratio, and flexural rigidity of the pipe-on-pipe response. From the results of the parametric study, it is noticed that peak pipe deformation increases with increasing the TNT charge weight and decreases with increasing the magnitude of standoff distance, damping ratio, and flexural rigidity of the pipe. The proposed formulation can be adopted in the initial design stage for rapid estimation of buried pipe responses subjected to underground blast load.

This paper presents a new approach for calculating seismic passive earth pressure, its point of application, and the approximate stress-state within the rupture wedge. The method of vertical slices combined with the limit-equilibrium (LE) technique was used as the framework for the analysis. While the available LE analyses used the rupture surface of predefined shapes, in this approach, the rupture surface is derived through the analysis. First, the mobilized soil behind the wall was split into thin vertical slices and the rupture plane of every slice was calculated by enforcing the Mohr–Coulomb failure criterion. Thereafter, by adding those rupture planes consecutively, starting from the wall toe, the passive rupture surface was achieved. The inclination of the rupture planes is guided by the soil friction angle, wall friction angle, seismic acceleration, and slice-interface friction angle. The distribution of slice-interface friction angle across the rupture plane was presumed to obey a power function. The exponent of the power function, the seismic passive earth pressure, and its point of application were derived concurrently by satisfying the static equilibrium conditions of the slices and applying a boundary condition. The results show that the outline of the rupture surface is guided by the slice-interface friction angle, and the shape is curvilinear for rough walls. With increasing seismic acceleration, the passive pressure decreases, and the point of application moves predominantly downward for loose sands. The obtained results were compared with those of previous numerical and experimental studies and were found to show good agreement, thus demonstrating the validity of the proposed method.