International Journal of Geomechanics

Soil disturbance induced by the installation of vertical drains reduces the horizontal soil permeability and shear strength in the disturbed zone. Thus, the soil disturbance contributes to the reduced overconsolidation ratio (OCR) of the soil in the vicinity of drains, influencing soil deformation. Although a significant amount of research has been conducted on the effect of permeability variations in the smear zone, the influence of the reduced shear strength in the smear zone on the ground behavior has not been investigated. In this study, a numerical solution adopting an elastic-viscoplastic model with nonlinear creep function in combination with the consolidation equations has been developed. Moreover, the effects of shear strength variation in the disturbed zone on the time-dependent behavior of soft soil deposits improved with vertical drains and preloading have been studied. The applied elastic-viscoplastic model is based on the framework of the modified Cam-clay model, capturing soil creep during excess pore-water pressure dissipation. Furthermore, nonlinear variations of the creep coefficient with stress and time as well as the permeability variations during the consolidation process are considered. The predicted results have been compared with available field measurements. According to the results, the OCR profile of the disturbed zone influences the viscoplastic strain rate, the creep strain limit, and consequently the soil deformation.

Based on fuzzy evaluation and the analysis hierarchy process, this paper develops a method for evaluating the self-healing capability of asphalt mixtures. In developing the method, 18 judgment indicators were selected on the basis of a study on the influence factors of self-healing capability, and a numerical approach was established to describe the properties of these indicators. Four types of subordinate functions with 16 mathematical expressions were set up to describe the properties of the continuous indicators, and empirical approaches were used to deal with the dispersion indicators. Based on the improved analysis hierarchy process, a renovated comprehensive multilevel evaluation method was developed to evaluate the self-healing capability of asphalt mixtures. Finally, the feasibility and effectiveness of the method were validated with excellent results using a type of asphalt mixture from engineering practice.

Geotechnical analyses are usually made before superstructure members are fully defined. The behavior of long-span buildings differs from the behavior of short-span buildings. Expensive solutions to the differential settlement that is calculated in geotechnical reports may be preferable but do not necessarily consider the superstructure’s rigidity effect. This paper examines the effect of the superstructure’s rigidity on the contact stress and the differential settlement for plane 2-bay frames. The plane frames consisted of flat slabs with hinged or fixed connections to the walls. The foundation system consisted of strip footings without tie beams to connect the footings due to the large span of the frames. The effect of superstructure rigidity on the damping of differential settlement owing to the redistribution of loads was investigated. The use of a slightly rigid superstructure may be the solution to differential settlement without the need for additional, more expensive methods. Five groups with 54 2-bay frames with different rigidities were modeled using a geotechnical finite-element program. The groups represented the main factors that affect the frame-soil system rigidity. No impact of footing rigidity on the average contact stress under the footings or on the maximum settlement was investigated. However, the rigidity of the footings also influences the distribution of the contact stress under the footing itself. The rigidities of the walls and slabs have significant effects on the resultant average contact stresses and on the maximum settlements under the footings, which affect the differential settlements. Analyses charts and new equations are presented to calculate the average contact stress and maximum settlements under the inner and outer footings for plane 2-bay frames. Therefore, the differential settlement can be depicted with consideration given to superstructure rigidity. The new straining actions of the superstructure’s walls also are presented.

In this paper, a model for damage and fracture, considering the heterogeneity of material properties, is validated and used to investigate the mechanism of spallation in fiber-reinforced concrete (FRC) slabs with various fiber and aggregate contents under impact loading. Numerical simulations show that there is a marked difference in the failure patterns among slabs with various fiber and aggregate contents, and the fibers can remarkably improve the tensile strength of the concrete slab, effectively prevent the initiation and propagation of cracks, and inhibit the occurrence of spallation. Moreover, numerical simulations capture the whole process of the propagation of incident compressive stress waves in the FRC and the reflection of stress waves upon concrete surfaces and the spallation failure of FRC induced by the reflected tensile stress wave, which is obviously different from the failure pattern of FRC under static loads. The results of this study can also provide a valuable reference for studies on the tensile properties and failure modes of heterogeneous quasi-brittle materials and the design of FRC slabs with appropriate fiber contents.

Cracking is a major distress in steel bridge deck pavements. To determine the critical cracking zone, a numerical multiscale structural analysis was proposed and performed on the basis of a case study. First, a whole bridge model was analyzed, which revealed that the critical segment under critical load combination was one-fourth of the bridge span. Second, the critical segment was modeled using the finite mixed element method, and the critical local plate was determined. Third, using a submodel technique, the critical orthotropic steel plate with pavement was analyzed. The constructed model was then updated through an equivalent impact factor obtained from a numerical model analysis that considered vehicle–pavement interaction. From such multiscale model analysis, the crack distribution law of steel deck pavements was determined. Comparison of the analysis results from a traditional model with the multiscale model revealed the non-negligible effects of bridge structure and pavement evenness. Findings from this study may provide guidance for improving the preservation practice of steel deck pavements.

In this study, the efficiency of proposed formulations for plane-strain modeling of vertical drain–assisted consolidation was evaluated. For this aim, the vertical drain–assisted preloading process was experimentally simulated using a fully instrumented large-scale Rowe cell. Nine pore-water-pressure transducers were installed in various locations to measure the changes in pore-water pressure during the test. Two pressure/volume controllers were connected to an infinite-volume controller to provide continuous water flow. Soft clays with predefined properties were used to form the intact and smear zones. A numerical code was developed by using the finite-difference program FLAC 2D to simulate the consolidation test. A numerical study was conducted to evaluate the efficiency of the proposed solutions for converting the axisymmetric state to a plane-strain condition and was subsequently compared with corresponding numerical analysis. From the results, it is observed that some of the proposed methods resulted in more accurate predictions of settlement and changes of pore-water pressure in the early stages of the consolidation process, whereas other proposed methods performed more accurately in the later stages of consolidation. Thus, three-dimensional modeling with actual soil-permeability properties to simulate the time-dependent behavior of soft soil improved with vertical drains is recommended.

This paper presents a theoretical and experimental analysis of an anomalous data detection treatment for roller-integrated compaction measurement (RICM) data. Anomalous data, which may be discovered during the collection of the RICM data, can significantly influence the evaluation of the compaction quality and misrepresent the real compaction situation of the layer. Two types of anomalous data are investigated, and corresponding methods are presented to identify these types. A bidimensional anomalous data identification method is proposed to distinguish anomalous data in calibration tests, and a neighboring weighted-estimation method is presented to reject anomalous data during the compaction quality assessment. The RICM data from three field construction sites are analyzed to verify the applicability and validity of the proposed methods. The results suggest that the first method renders a more accurate correlation, whereas the second method improves the precision of the compaction evaluation.

A comprehensive strut-and-tie model is a function of the nodes, struts, ties, model types, and pile reaction force. Because each element has more than one solution, the function is a problem of permutations and combinations. This paper presents a new strut-and-tie model that yields a satisfactory simulation result. In the model, a model type of truss action, direct arch action, or a combination of both actions was selected independently for the side and angle piles. The node and tie parameters were also modified. The pile reaction force distribution and the failure mechanism for inclined struts were also considered. However, because the authors’ previous study did not include a detailed analysis or an in-depth exploration, the effect of these critical factors is discussed in this paper at length. The model, which was programmed using the MATLAB language, was used to sequentially analyze the possible solutions for each member (nodes, ties, and struts). Different solutions for the ratio of truss action and direct arch action were also compared. The inclined struts with variable cross sections were tested under various failure mechanisms. Furthermore, the effect of the pile reaction force, which was distributed using model test measurements and theoretical (elastic or rigid) analyses, was analyzed. Comparison of the solutions indicated that the function $f$, which included the essential elements described above, was both rational and accurate.

Having the advantages of high permeability and high strength, pervious concrete is suitable for improving ground-bearing capacity. In the Yellow River Delta, a pervious concrete pile (PCP) composite foundation has been constructed to reduce settlement of an expressway embankment. To study the working mechanism of PCPs, a numerical model was constructed based on the finite-difference method and Biot’s consolidation theory, which was validated by data from in situ tests. The excess pore-water pressure, pile–soil stress ratio, lateral displacement, and settlement of the PCP composite foundation under the loading of the road embankment were numerically calculated and compared with those of gravel pile and low-grade concrete pile composite foundations. Comparisons show that the dissipation of excess pore-water pressure in the PCP composite foundation was fastest, which implied that PCPs can significantly mitigate the development of excess pore-water pressure and thus enhance subsoil strength. Furthermore, the PCP composite foundation showed minimal postconstruction settlement and lateral displacement. Therefore, PCP is particularly suitable for reinforcing subsoil that has low strength and poor permeability.

Geosynthetics such as geogrids or geotextiles are often used for the reinforcement of weak soils. Much research has been performed to investigate the bearing capacity of reinforced shallow foundations using the limit equilibrium method with Mohr–Coulomb failure criterion. In this paper, the loading behavior of reinforced strip footings was studied numerically using a commercial finite difference program with a double-yield soil model. First, the load–settlement curve of an unreinforced strip footing was simulated using both Mohr–Coulomb failure criterion and the double-yield model. The simulated bearing capacities were then compared with Terzaghi’s solution. The effects of various parameters, such as burial depth and length of the reinforcement, as well as arrangement of two reinforcement layers, were also studied. Results of this study indicate that the loading behavior of strip footings simulated with the double-yield model is more realistic, and the optimum burial depth and length of reinforcement obtained from this study also agree with values reported by previous investigators.

Sokolovskii’s method of characteristics is extended to provide analytical solutions for the ultimate load at the moment of plastic failure under plane-strain conditions of shallow strip foundations on weightless rigid-plastic media with a noncohesive power-law failure envelope. The formulation is made parametrically in terms of the instantaneous friction angle, and the key idea to obtain the bearing capacity is that information can be transmitted from the free surface (where external loads are known) to the contact plane of the foundation. The methodology can consider foundations adjacent to a slope, external surcharges at the free surface, and inclined loads (both on the slope and on the foundation). Sensitivity analyses illustrate the influence on bearing capacity of changes in the different geometrical parameters involved. An application example is presented and design plots are provided, and model predictions are compared with results of bearing capacity tests under low gravity.

This paper presents an experimental study on the shear behavior of granular materials, focusing on the effects of interparticle friction and particle size, which are of fundamental importance but are not yet well understood. The experimental program consisted of a large number of direct shear tests on glass beads of varying sizes and interparticle friction conditions, performed under a range of packing densities and normal stress levels. Test data were interpreted in terms of the stress–dilatancy relationship and shear strength parameters. The study indicates that under otherwise similar testing conditions, oil-lubricated glass beads tend to have substantially lower shear strength as compared with water-lubricated, water-flooded, and dry glass beads. It has also been found that at similar particle size uniformity, increasing mean particle size ($d_{50}$) leads to more dilatant shear response and higher shear strength. A generalized stress–dilatancy relation is proposed, which introduces a variable dilatancy coefficient that reflects on the effects of interparticle friction and particle size. It is shown that classical stress–dilatancy relations can be regarded as special cases of this generalized case, with the dilatancy coefficient being taken as a constant. Further explanations for the observed effects on macroscopic behavior are provided from the micromechanics perspectives.

This study develops an analytical approach to quantitatively model the efficiency of the pretensioning of grouted rockbolts in terms of reduction of tunnel convergence. In this study, the distribution of force along the pretensioned fully grouted bolt is calculated by the assumption of a rigid connection between the bolt and the rock mass. A compressive force is then applied to the bolt head on the tunnel surface to consider the shear relative displacement between the bolt and the rock mass. The magnitude of this compressive force is found by modeling the bolt boundaries’ stiffness. The theoretical proposed approach is simplified to be used for practical purposes. The results show that if the stiff end plate is tightened to the bolt head (complete planner contact), the grouting effect of the pretensioned fully grouted bolts on tunnel stability can be neglected.

A three-dimensional (3D) finite-element program has been developed for the dynamic analysis of pile groups. Soil and pile media have been discretized into 3D isoparametric continuum elements. To simulate the stress transfer between soil and pile under lateral load, surface elements have been introduced at the interface. To avoid the radiation effect due to dynamic loading, it is proposed to use the appropriate boundary conditions with introduction of Kelvin elements at the transmitting boundary. The displacements at each time step are evaluated using the implicit Newmark-beta integration method. In the iterative procedure, stresses at a given Gauss point are first checked and adjusted against a limiting tension criterion, and then these stresses are further checked against a yield criterion. Extra stresses computed during these checks are converted to load vectors that are applied in the next iteration. A parametric study is carried out to consider the effect of pile spacing, number of piles, arrangement of pile, and soil modulus on the response of pile group.

The present study investigates the possibility of torsional surface wave propagation in a fiber composite layer lying over an initially stressed viscoelastic half-space. The closed-form expression for the dispersion relation and damping equation has been obtained. Viscoelasticity of the lower half-space, reinforcement, wave number, and horizontal compressive/tensile initial stress acting in an initially stressed lower half-space have substantial effect on the dispersion curve. For the sake of comparative study, numerical computation and graphical demonstration have been carried out by considering some of the special cases of the problem in addition to the problem itself. A remarkable finding is that reinforcement in the superficial layer favors more the phase velocity and damped velocity of a torsional surface wave as compared with the reinforced free superficial layer. As a special case of the problem, it is found that the obtained dispersion relation is well in agreement with the classical Love wave equation.

The present study addresses the effect of interference on the uplift capacity of two closely spaced horizontal strip anchors embedded in cohesionless soil. The analysis has been performed using the method of stress characteristics coupled with the limit equilibrium approach. The method consumes fewer assumptions and provides a zone in which the force equilibrium and plastic yield conditions are simultaneously satisfied for given boundary stresses. The effects of surcharge and unit weight of soil on the pullout resistance of anchors have been determined in terms of uplift capacity factors ($F_q$ and $F_{\gamma }$) and are presented as functions of embedment ratio ($\lambda$) and angle of internal friction of soil ($\varphi$). Similarly, the interaction phenomenon of two closely placed anchors has been expressed in terms of efficiency factors (${\xi }_q$ and ${\xi }_{\gamma }$). A detailed parametric study has been carried out by varying the clear spacing ($S$) between two anchors, embedment ratio, and soil friction angle. The results of the numerical analysis are compared with the available theoretical and experimental data reported in the literature.

The paper evaluates the destructuration and creep properties of soft sensitive Perniö clay during one-dimensional consolidation. Incremental loading oedometer tests presented herein were part of an extensive testing program performed on natural and reconstituted samples of Perniö clay. Given the experimental results, general stress–strain compression curves were investigated taking into consideration the effects of clay structure and sample quality. The effect of sample disturbance on preconsolidation pressure was quantitatively evaluated by an exponential relationship. Compression parameters accounted for the detailed stress-dependent behavior. The assumption that the $C_{\mathit{ae}}/C_c$ ratio would be constant in one-dimensional consolidation was proven wrong. Three new sensitivity approaches were developed and proved to be feasible in comparison with sensitivity determined by fall cone tests. The developed sensitivity indices were exponentially related to the initial void ratio $e_0$. The stress–strain–strain rate isotaches were plotted to explore the gradual destructuration process at different strain rates. For Perniö clay, the $v-{\sigma }_v^{\prime }$ isotaches coupled with strain rates were neither parallel in linear nor natural logarithmic scale. Special attention was given to the tangent modulus theory, which was used to analyze the complete destructuration process of natural clay. The defined characteristic parameters were interpreted, taking into account sampling depth and sample quality.

Installation of stone columns is one of the most popular ground improvement techniques used to improve the strength of soft soil. Owing to the presence of more pores in the stone column, it acts as a drainage path for seepage of water from the soil during consolidation. Thus, in addition to increasing the soil’s strength, the stone column also increases the rate of consolidation of the soil. The water present in the pores of the soil is not pure, and some fine particles released from the soil are also present. During the seepage, these fines present in the fluid also move along with it. Depending upon the amount of concentration of fines present in the seepage water, the clogging of the stone column takes place which reduces the permeability of the stone column. Thus, the rate of consolidation of the ground improved by the stone column also decreases because of the clogging. In the present study, a mathematical model for the consolidation rate of soil improved with stone columns has been developed by considering the effect of clogging due to particle migration. The results are compared with the available rate of consolidation models for stone column–improved ground with or without clogging. The effects of various ranges of parameters of the developed model on the rate of consolidation are also studied. It is observed that as the diameter ratio and stress concentration ratio increase, the clogging also increases.

In this paper, the effect of fine content in the retained sandy soil on the behavior of braced excavation has been studied using experimental and numerical models in terms of four design factors: strut force, bending moment developed in the wall, lateral deflection of the wall, and vertical displacement of the ground surface. In the experiments, the fine content of the soil has been estimated as 0, 5, and 10% (by weight). However, the numerical study has been conducted for different fine contents varying from 0 to 50% (by weight). The parametric study with 20 m depth of retaining wall; position of struts at 2, 7, 12, and 17 m below ground level; wall thickness and embedment depth as 6 and 80% of depth of excavation; and stiffness of support members as $5\times {10}^5\mathrm{kN}/\mathrm{m}/\mathrm{m}$ confirms that the values of the four design factors (strut force, wall moment, lateral wall defection, ground deflection, and net earth pressure acting on the wall) increase with the increase in fine content in the retained soil. It is also observed that predominant ground surface displacement gradually shifts from heaving to settlement as the fine content in the retained soil increases.

A uniform gradient (UG) element formulation for a four-node quadrilateral element is derived and implemented for solving the fully coupled governing equations for the dynamics of a saturated porous medium. An hourglass control scheme is also derived for eliminating the hourglass modes that arise when using the UG element formulation. The effectiveness of the new formulations is investigated by simulating the quasi-static and dynamics response of a footing and the dynamic response of an earth dam. The results show that the level of excitation of hourglass modes is problem-dependent and mesh-dependent. The proposed method for controlling the hourglass modes is shown to be effective with minimal effect on the computed response.

In this study, numerical simulation was conducted to model the behavior of rockbolts with free-end slip in tension. A nonlinear bond–slip relationship was input to the numerical model to represent the interaction mechanism of the interface between rockbolt and grout. The results of the model were validated against laboratory tests. The numerical model matched the experimental results in terms of load–displacement relationship, rockbolt strain distribution, and interfacial shear-stress distribution. This paper indicates that (1) the rockbolt element in the numerical model is capable of describing the strain-softening behavior of the rockbolt–grout interface; and (2) the pullout tests of rockbolts with free-end slip can be used to derive the bond–slip relationship, and thus provide insights into the mechanical behavior of rockbolts with free-end slip.

The quality of cement-treated soil columns is usually assessed by examining the strength of cored samples. This paper presents a finite-element analysis approach with random field theory for assessing the quality of a cement-treated soil column from which cored samples are retrieved. Monte Carlo simulations with conditional distribution (conditional simulation) were conducted to generate spatial dependence random fields with the data known at some locations. Simulations without the known data (unconditional simulation) were also performed for comparison. Using the random field samples generated from the Monte Carlo simulations, finite-element analysis was performed to simulate the compression behavior of a full-scale column in which material properties vary with a presence of spatial autocorrelation. Finite-element analysis with conditional simulation predicts the overall strength of a targeted cement-treated soil column appropriately, and the overall strength variability obtained with the conditional simulation is lower than that obtained with the unconditional simulation. The results suggest that the conditional simulation offers advantages over the unconditional simulation when assessing the probability of failure of a cement-treated soil column with large autocorrelation distance.

Recycling or reuse of scrap tires in civil engineering projects has gained significant research attention in recent years. Experimental investigation reports suggest that inclusion of tire chips in sand increases the shear strength and decreases the dilatancy of sand implying the promising and environmentally sustainable use of sand–tire chip (STCh) mixture in civil engineering projects. However, only a few constitutive models have been developed to predict the monotonic behavior of STCh mixtures. In this paper, a semiempirical constitutive model has been developed using the critical state framework, which takes into account the constant stress ratio and state parameter ($\psi$) to capture the key features exhibited by the STCh mixture during shear loading. The model has been validated with extensive laboratory investigation results. It has been shown that the model can effectively simulate the monotonic behavior of the STCh mixture.

Finding an optimum reinforcement layout for underground excavation can result in a safer and more economical design, and is therefore highly desirable. Some works in the literature have applied topology optimization in tunnel reinforcement design in which reinforced rock is modeled as homogenized isotropic material. Optimization results, therefore, do not clearly show reinforcement distributions, leading to difficulties in explaining the final outcomes. To overcome this deficiency, a more sophisticated modeling technique in which reinforcements are explicitly modeled as truss elements embedded in rock mass media is used. An optimization algorithm extending the solid isotropic material with penalization method is introduced to seek for an optimal bolt layout. To obtain the stiffest structure with a given amount of reinforced material, external work along the opening is selected as the objective function with a constraint on the volume of reinforcement. The presented technique does not depend on material models used for rock and reinforcements and can be applied to any material model. Nonlinear material behavior of rock and reinforcement is considered in this work. Through solving some typical examples, the proposed approach is proved to enhance the conventional reinforcement design and provide clear and practical reinforcement layouts.

Concrete-faced rockfill dams (CFRDs) are commonly built around the world. As energy demands soar and construction methods evolve, the interest in the construction of CFRDs with larger heights has increased tremendously. However, because of the construction of higher CFRDs, some dams have experienced considerable fractures at the concrete faces. Well-known cases include Campos Novos (Brazil), Barra Grande (Brazil), and Mohale (South Africa), where in some instances these cracks have led to dewatering of the reservoirs to allow for the concrete slabs’ repairs. The development of these fractures may be attributed to the highly deformable rockfill body. In general, the state-of-the-art design of CFRDs is mostly based on common practice rather than rigorous analysis procedures. And as such, cracking problems because of deformability of the rockfill may not be properly predicted unless a detailed analysis is performed. In this work, a new framework for the analysis of CFRDs is developed that is capable of predicting the possible failure of a concrete facing. As part of this framework, a comprehensive nonlinear finite-element analysis scheme is developed to model the construction sequence, the contact interaction between the concrete facing and the rockfill body, and the impounding of the reservoir. As a case study, using the developed framework, the Kárahnjúkar CFRD (Iceland, 198 m in height) is analyzed, the results are validated by the field measurements, and suggestions for mitigation measures are provided. This methodology, based on the results of the investigation, provides guidelines and establishes a framework for analysis of CFRDs that can be used for design purposes.

The uplift capacity of shallow horizontal strip anchors embedded in cohesionless soil has been obtained under seismic conditions. The limit equilibrium approach with log spiral failure surface together with modified pseudodynamic seismic forces has been adopted. In this modified pseudo dynamic approach, the soil is assumed to behave as a viscoelastic material overlying a rigid stratum and subjected to harmonic horizontal acceleration. This modified methodology satisfies the zero-stress boundary condition at the free ground surface. In the present methodology, the amplification of seismic acceleration depends on the soil properties and can be evaluated; hence, there is no need for assumption of any amplification value as is usually done in the literature. It is observed that the seismic acceleration distribution along the depth is highly nonlinear. The net seismic vertical uplift capacity factor for a unit weight component of soil ($F_{\gamma d}$) is estimated. The results under static and seismic conditions are determined for various combinations of input parameters, such as soil friction angle, embedment ratio, and seismic acceleration. It is observed that the design value of $F_{\gamma d}$ decreases significantly with an increase in seismic acceleration. As expected, the seismic uplift capacity increases with an increase in embedment ratio and soil friction angle. Results in terms of nondimensional net seismic uplift capacity factor are presented in graphical form. In addition, the present results are compared and found to be in good agreement with a very few available similar results in literature. The present study reveals the lowest critical design values of seismic uplift capacity factor that may be used in seismic design of shallow strip anchors.

In a previous study, three-dimensional (3D) linear and simplified nonlinear finite-element soil response methods based on a horizontal-component input seismic wave field were proposed. A seismic wave field means seismic waves propagating in a 3D medium. The method had been developed with the goal of adequately treating short-period (less than a few seconds) seismic surface waves trapped by a deep (several km) underground structure in a shallow soil model. In the present study, along with improvements of the methods, 3D linear and simplified nonlinear soil response methods based on a three-component input seismic wave field are developed, and are applied to estimate seismic soil responses in the three geotechnical zones (the reclaimed, alluvial, and hill zones) of Tokyo during two large earthquakes. The more reasonable soil responses revealed that, in a practical sense, vertical ground motions affected soil responses very little. They also clarified large effects of liquefaction in the reclaimed zone and inferred no large ground failure in the alluvial and hill zones.

The influence of the intermediate stress ratio on the mechanical behavior of granular materials under generalized stress conditions is not well understood, particularly in regard to relationships between macroscale behavior and microscale response. The objective of this paper is to study the influence of the intermediate stress ratio, specified by $b[=({\sigma }_2-{\sigma }_3)/({\sigma }_1-{\sigma }_3)]$, on the mechanical behavior of granular materials under generalized stress conditions, using the discrete element method (DEM). Selected $b$ values were used to illustrate the influence of the intermediate principal stress ${\sigma }_2$ on the major and minor principal stresses, ${\sigma }_1$ and ${\sigma }_3$, respectively. More-generalized stress conditions were identified by continuously varying $b$ values. Specifically, 11 stress paths under truly triaxial conditions, following the stress-controlled method for a three-dimensional sphere, were simulated with continuously varying $b$ values as well as constant $b$ values. Differences in the stress–strain relationship results were studied, including the relationship among principal normal strains and principal deviatoric strains as well as the evolution of stress-increment and strain-increment vectors and the behavior of strain-increment vectors on the $\pi$ plane. The DEM results were found to compare well with the experimental data qualitatively. The macro behavior and micro response data were described by the relationship between the stress ratio and the fabric structures representing contacts of all particles as well as strong contact regardless of varying $b$ value.

Many situations exist where foundations must be constructed on or near slopes. As a result, the foundation’s bearing capacity is reduced, and the slope might collapse. This paper presents the results of laboratory and numerical model tests on the influence of soil confinement on the behavior of a model footing adjacent to slopes. Confining cylinders with different heights, each set back some distance from the slope crest, were adopted. The ultimate bearing capacity of a circular footing supported on a confined sand bed adjacent to a slope was studied. The studied parameters include the cell-embedment depth, slope angle, and subgrade density. The results indicate that the bearing load capacities of circular footings at any edge distance from the slope crest can be appreciably increased by soil confinement. The slope effect on the ultimate bearing capacity can be neglected when the cell-footing system is placed at setback distance with cell-embedment depth around two times the cell diameter. When the cell-footing system is placed directly on a steep slope crest, the improvement in the bearing capacity reached 4, 2.2, and 1.9 times the footing with subgrade relative densities of 80, 55, and 35%, respectively. The numerical analysis helped to explain the deformation behavior of cell-footing soil systems adjacent to a slope. It provides a realistic failure mechanism of the new system and illustrates how the cell can protect the slope from collapse by decreasing slope deformation.

Liquefaction-induced ground displacements resulting from earthquake shaking are a major cause of damage to earth structures comprised of, or underlain by, loose saturated granular soils. The present paper describes the results of numerical modeling of an embankment founded on loose liquefiable deposit using PLAXIS three-dimensional finite-element software. Acceleration base-input excitation of the El Centro earthquake has been applied to the model monitoring the displacements, liquefaction potential, and excess pore pressures (EPPs). A modified nonassociative plastic-potential function depending on the Drucker–Prager criterion is used to maintain the coaxiality of stress strain in the deviator plane for a stress path initiated from an isotropic line. The soil-densification rule is also added to predict more realistic EPPs in seismic loading. The countermeasures considered are densification of the sand layer by compaction and sheet pile enclosure. The dynamic behavior of the used embankment-foundation and liquefaction countermeasure systems are also presented. The sheet pile measure is effective in controlling the displacements but has marginal effect on EPP. The soil-column countermeasure was the most effective case in limiting the development of EPPs and displacement beneath the embankment. The results of this study show that numerical simulation of earthquake effects on embankments with liquefiable foundations with and without remedial measures is possible using data from conventional laboratory tests and a verified numerical procedure.

When modeling the seepage process in a variably saturated porous medium, it is crucial to properly characterize the effects of hydraulic hysteresis. In this paper, a theoretical model of two-phase flow in porous media is introduced, in which an internal state variable-based model of capillary hysteresis is incorporated. Using this theoretical model, a fully coupled finite-element procedure is developed and implemented into a computer code. The numerical procedure is used to simulate the two-phase flow in the unsaturated soils experiencing various drying/wetting cycles. The simulative results are then compared with the experimental data available in existing literature, showing that the proposed procedure is capable of simulating the two-phase flow processes in the porous media subjected to arbitrary drying/wetting cycles. It is demonstrated that under a nonmonotonic flow condition, the effects of hydraulic hysteresis on the water infiltration and redistribution processes in a soil-column test are significant, and in addition, the effects of air phase cannot be neglected. Noticeably, the proposed procedure can be used to track the hydraulic paths that a soil layer experiences, and hence, the procedure is useful in modeling the water infiltration and moisture redistribution processes in soil layers during a long-term intermittent precipitation event or nonmonotonic underground water-table variation.

The influences of particle breakage on the position of the critical state line (CSL) were systematically investigated in this paper through a series of large-scale triaxial compression tests on Tacheng rockfill material (TRM). It was found that the critical-state stress ratio of TRM (i.e., the gradient of the CSL in the $p-q$ space) was approximately regarded as a constant. In the $e-\log p$ space, the CSL of TRM descended with a decrease in the initial void ratio, whereas the gradient of the CSL was constant. A procedure was established for evaluating the critical state point at a same particle breakage, which comprised the breakage critical state line (BCSL). An increase of the particle breakage led to not only a vertical translation but also a rotation on the BCSL of TRM in the $e-\log p$ space, which was similar to the observation of Dog’s Bay sand. Consequently, the initial gradation (or the corresponding initial void ratio) was the dominant factor that affected the position of the CSL of TRM in the $e-\log p$ space.

Growing urbanization is leading to more structures being constructed close to each other, resulting in substantial interaction between their foundations. Although the interaction between two shallow foundations and between piles in a pile group has been studied by several researchers, the effects of interaction between shallow and deep foundations are not very well understood or studied. Not much published literature is available for practicing engineers to analyze and design shallow and deep foundations that are constructed adjacent to each other. The second author of this paper was recently involved in a project in which a structure designed to be supported on drilled shafts was supposed to be constructed adjacent to another structure designed to be supported on a large mat foundation with high floor load. Although the authors have performed a detailed parametric study using finite-element techniques to better understand stress distributions and develop a simplified method to analyze this type of problem, this paper is only focused on estimating lateral stresses on the shafts and their lateral load analysis. A stress bulb for lateral stresses under a uniformly loaded square foundation is proposed, which is a significant tool for practicing engineers to understand lateral stress distribution below a uniformly loaded square area and estimate lateral stresses on nearby deep foundations.

Steel catenary risers (SCR) are widely used in deepwater oil and gas production. The riser–seabed–water interaction near the touchdown zone is one of the main concerns in the design of fatigue life of SCR. During upward displacement, suction develops under the riser and a trench might be formed when it separates from the seabed near the touchdown point. In the subsequent downward movement, the riser penetrates through this trench to the seabed. Therefore, modeling of suction and trench formation is very important. In the existing models available in the literature for uplift resistance, these factors are incorporated using empirical relationships. It is also recognized that the available finite-element (FE) modeling techniques for this large-deformation problem are computationally very expensive, although penetration behavior can be simulated. In the present research program, both penetration and uplift behavior are simulated using FE and computational fluid dynamics (CFD) approaches. The simulation results for penetration are presented in Hawlader et al. (2014). In this paper, CFD simulations of uplift resistance, suction and trench formation using ANSYS CFX are discussed. A new model for undrained shear strength of soft clay is proposed that is applicable to a wide range of shear strain rates. The effects of strain rate and strength degradation are incorporated properly in ANSYS CFX and simulations are performed for one penetration-uplift cycle. Comparing with empirical models developed from experimental results and also with FE results for idealized conditions, it is shown that the present CFX model can simulate the suction and uplift resistance. Moreover, the CFX model developed in this study using the subdomain approach is computationally very efficient. The suction under the riser is the main source of uplift resistance for shallow embedments. The parametric study shows that the maximum uplift resistance and depth of trench depend on uplift velocity and the undrained shear strength of clay.

The scaled boundary FEM (SBFEM) has become an attractive alternative to traditional rigorous methods available for modeling the unbounded media for soil–structure interaction (SSI) analysis using the substructure method. Most of the coupled FEM–SBFEM schemes available in the literature are only for the linear-elastic SSI analysis. Very few studies have considered the nonlinearity in the near-field, and most of them have adopted elastic-perfectly plastic models to simulate the nonlinearity. In the present study, an advanced plasticity-based model known as hierarchical single surface $(\text{HiSS})\text{-}{\delta }_0$, which is based on isotropic hardening and associated response, has been implemented in the coupled FEM–SBFEM scheme in the time domain. The HiSS model provides a general formulation for the elastoplastic characterization of the material behavior. Problems from the literature have been solved using the presently developed code, and the results have been verified, thus validating the developed code.

Estimating the mechanical properties of nonpersistent jointed rock masses is one of the most challenging problems in practical rock engineering due to the complex interaction of rock joints and intact-rock bridges. In this paper, the effect of joint geometrical parameters of nonpersistent rock mass on uniaxial compressive strength (UCS) and the deformation modulus was studied by using the discrete-element particle flow code PFC3D. In this numerical approach, the intact material is represented by an assembly of spherical particles bonded together at their contact points, and the joint interface is explicitly simulated by slip surfaces that are applied at contacts between the particles lying on the opposite sides of the joint interface. The failure process is simulated by the breakage of bonds between particles. A previous study of the authors has shown that this approach is capable of reproducing the mechanical behavior of nonpersistent jointed rock masses by a comparative study against physical experiments. In this study, the effect of joint geometrical parameters, including joint-orientation angle, spacing, persistency degree, step angle, and aperture, on the UCS ${\sigma }_{\mathit{cm}}$ and the deformation modulus $E_m$ was studied. To reduce the number of experiments and also gain a sound understanding of the effect of each parameter, experiments were designed using a well-established experiment design technique. Five failure modes were observed in the experiments, including intact failure, step path, block rotation, semiblock generation, and planar failure. It was found that the initiation and propagation of tensile cracks have a controlling effect on the observed failure modes. The ${\sigma }_{\mathit{cm}}$ and $E_m$ of jointed samples were analyzed using analysis of variance. It was found that joint-orientation angle, spacing, and persistency have a significant effect on both ${\sigma }_{\mathit{cm}}$ and $E_m$ and that joint-orientation angle has the greatest effect on the mechanical behavior of a rock mass.

A numerically stable and computationally efficient finite-element model for analyzing the dynamic response of unsaturated soil profiles in terms of total stresses is presented in this paper. The highly nonlinear, fully coupled governing differential equations are simplified by neglecting the relative accelerations and velocities of the pore fluids, and the simplified formulation is improved by incorporating an external viscous damping formulation for unsaturated soil. The surface spectral accelerations computed using the proposed model are qualitatively compared with that of DEEPSOIL and PLAXIS following a comparison of surface spectral accelerations computed using the underdamped and the damped simplified formulations. A detailed parametric study of the effect of viscous damping parameters and both elastoplastic and elastic constitutive models is also presented. A simplified soil–pile interaction study is presented to show the effect of soil–pile interaction on the computed responses. Analysis reveals that the proposed model is applicable to the seismic site response analysis of unsaturated soil profiles.

An analytical solution is developed in this paper to investigate the vertical vibration of a pipe pile in viscoelastic soil. The soil is assumed to be a homogeneous and isotropic layer. The pipe pile is considered as a one-dimensional Euler rod. Considering both the vertical and radial displacements of the outer and inner soils and the soil pile–coupled vibration, the dynamic equilibrium equations of the soil and pile are established. The dilatations of the outer and inner soil are obtained by differential transformation on the equations of soil and the variable separation method. Then, the vertical and radial displacements of the outer and inner soils are obtained. The displacement response and impedance function of the pipe pile are derived using the continuity assumption of the displacement and stress between the piles and the soils. Numerical examples are presented to analyze the vibration characteristics of the pile.

Carbonate sands that are specific soils have some unusual characteristics, such as particle crushability and compressibility, that distinguish their behavior from other types of soil. Because of their large diversity, they have a wide range of mechanical behavior. Recently, there have been many attempts to predict the mechanical behavior of carbonate sands, but all these attempts have been focused on experimental and case studies of some specific soils, and there is still no unique method that can consider all types of carbonate sands behavior and describe their various aspects. In the present study, two artificial intelligence-based models, namely artificial neural networks and support vector machines are used together and comparatively to predict the mechanical behavior of different carbonate sands. The models were trained and tested using a database that included results from a comprehensive set of triaxial tests on three carbonate sands. The predictions of the proposed models were compared with the experimental results. The comparison of the results indicates that the proposed approaches were accurate and reliable in representing the mechanical behavior of various carbonate sands.

The interaction of an applied axial load and a drag load on a circular pile in consolidating layered soil is investigated. A rigorous load-transfer theory with elastoplastic slip considered at the pile–soil interface for such piles is developed. The validity of the proposed solution is confirmed by a comparison with field measurements. Results of extensive parametric studies with regard to the pile behavior are presented for a better understanding of the behavior for axially loaded piles embedded in layered soil with an upper consolidating layer. Design charts are presented to predict the location of the neutral plane, maximum pile load, and pile top settlement for axially loaded piles in layered consolidating soils.