International Journal of Geomechanics

The discrete-element method (DEM) was employed in this study to analyze the micromechanical behavior of an axially loaded geogrid-encased stone column (GESC) installed in a clay bed. A three-dimensional DEM model was developed to simulate a partially encased stone column in the laboratory test under a plate loading condition. The aggregate, the geogrid encasement, and the surrounding soil were simulated using particles with different sizes and micromechanical properties. The load-displacement behavior of the DEM model closely matched the experimental result during the loading process. This study investigated the vertical and radial stresses in the column and its surrounding soil, the porosity change and particle movement in the column, and the contact force distributions before and after loading. The interaction and the interlocking effect between particles were different in the encased and unreinforced sections due to the existence of the geogrid encasement. The surrounding soil developed high vertical and radial stresses in the layers below the base of the geogrid encasement due to the strong interaction between the aggregate and the soil. The maximum coefficient of radial stress (2.4) in the encased column was approximately half the coefficient of passive earth pressure (4.6). The current design method overestimated the bearing capacity of the GESC based on the coefficient of passive earth pressure.

The ultimate bearing capacity of shallow foundations on unsaturated soils is investigated through the concept of suction-dependent effective stress. The first approach is a new analytical solution considering the influence of matric suction on ultimate bearing capacity by extending Vesic’s solution for saturated soils. Accordingly, a modification factor has been introduced as a nonlinear function of matric suction for tuning the cohesion-dependent component in the bearing capacity equation. The second approach is incorporating the unsaturated effective stress state in conjunction with the suction-dependent cohesion into a three-dimensional (3D) finite-difference code. In developing the 3D simulations, the variation in matric suction versus the depth of the soil was considered as well as the dependency of the degree of saturation on the soil suction. In addition, in three-dimensional numerical analyses, the input material parameters were modified to take into account the suction-stress concept in unsaturated soils. To assess the validity of the analytical and numerical approaches, four series of experimental data from physical plate load tests conducted under different matric suctions and embedment depths of the footing were selected. Accordingly, water retention curves of different test materials were considered as key input parameters used in both approaches to improve model predictions. Results from the analytical approach show the dependency of the presented correction factor on the soil properties, geometrical aspects of the foundation, and its embedding depth. In addition, the 3D numerical simulation revealed the suitable functionality of the effective stress approach on predicting the load-displacement behavior of shallow foundations on unsaturated soils. Moreover, the comparison between analytical, numerical, and experimental data shows a good conformance between the experimental test results, analytical solutions, and numerical predictions, especially for sandy soils.

In this paper, a systematic study was carried out to computationally explore the significance of different mechanisms involved in hydraulic fracturing treatments in practice, with special reference given to the hydrofracture inflow. For this reason, our well-established extended finite-element framework for modeling of hydraulic fracturing treatments in saturated porous media was employed. Accordingly, the $\mathbf{u}-p$ formulation was adopted to develop the coupled set of equations governing the hydromechanical response of the fractured porous media. The spatial discretization was carried out by means of the extended finite-element method (X-FEM) in order to incorporate the strong discontinuity in the displacement field due to the fracture body as well as the weak discontinuity in the pressure field due to the leak-off flow. Important mechanisms and parameters studied include proppant settlement, fracture energy, leak-off flow, fluid-lag zone, fracture surface roughness and tortuosity, pressure fluctuations, and flow regimes. By benchmarking the results against the reference solution obtained in the absence of the mechanism under consideration, a beneficial criterion for the significance of each mechanism was deduced.

Based on the strength criterion of the nonlinear spatially mobilized plane (SMP), an anisotropic nonlinear strength criterion is presented to accurately describe the strength anisotropy of geomaterial. An anisotropic variable with the friction coefficient of the nonlinear SMP strength criterion is introduced to account for the influence of anisotropy. A new criterion is illustrated on both the meridional and octahedral planes, which greatly simplifies the methods of capturing the anisotropy of geomaterials under various stress paths. In addition, only traditional triaxial tests are used to determine the model parameters of the criterion. The test results from sand, clay, and rock for the complex conditions of the true triaxial test and torsional shear test show that the anisotropic strength criterion can be utilized for various geotechnical materials. Compared with the prediction of test results mentioned in the relevant literature, the new criterion proposed in this paper can predict the anisotropic strength of various geotechnical materials.

Variable compressibility must be considered in settlement calculation of soft soil stratums, especially for thick soil layers. This study proposes a new simplified method to calculate the settlement of a thick soil layer with creep. It is a new simplified method because tedious numerical methods are avoided to obtain the total settlement including consolidation and creep settlement. The new simplified method is based on a mathematical solution for the consolidation analysis of a soil layer to consider nonlinear compressibility, and it is proposed to take $\alpha =U_z$ as a variable instead of a constant as in previous studies. A series of cases including different thicknesses of soil stratums, different OCR values, different surcharge loadings, and different values of creep parameter are studied to verify the new simplified method by comparing our calculated values with the finite-element (FE) simulated results. Subsequently, a typical and well-known Väsby test fill project with 50-year measured data was selected as a thick soil layer example to illustrate the feasibility of the new simplified method to be used in practice. Both the new simplified method and finite-element modeling were used to obtain ground settlements. It was found from the comparison that the calculated results from the new simplified method and the FE modeling were in good agreement with the measured data.

A reduced model for unsaturated flow in one-dimensional layered soils with local stochastic soil hydraulic conductivity is proposed. The reduced model relies on an improved closure assumption compared with straightforward truncation of moment equations for the statistics (expectation and covariance) of the volumetric water content, whereby certain higher-order moments can be expressed in terms of known quantities. The reduced model was compared numerically with (1) direct numerical simulations using homogenized soil properties and (2) agent-based stochastic direct numerical simulations, with soil hydraulic properties defined at the local (finite-difference cell) level. Numerical results showed that the reduced model successfully captures larger variations in water content of the unsaturated flow in heterogeneous soils compared with the solution resulting from homogenization.

The floor heave and the inward movement of sidewalls are often encountered in the excavation of tunnels with swelling rock properties. However, the deformation mechanism for swelling soft-rock tunnels cannot be reasonably revealed even now. In this paper, a time-dependent deformation mechanism is investigated in depth and the viscoelastoplastic deformation is obtained using a nonassociated flow rule and the modified Nishihara model. The continuous degradation behaviors of soft rock induced by the intercoupling between the stressed-dilation and the physicochemical swelling is considered based on the humidity field theory and the Zhang three-dimensional (3D) Hoek-Brown yield criterion. The results show that the time-dependent deformation exhibited is unstable in the secondary creep stage and tends to increase inversely with the values of the Zhang 3D Hoek-Brown criterion parameters and the elastic modulus, while it increases directly with the values of the humidity swelling coefficients and the Poisson’s ratio. The substability creep behavior occurs earlier with decreasing the relaxation time. Furthermore, the sensitivity law of incorporated parameters corresponds well with their corresponding physical meaning and practical significance in this study.

The unloading and reloading of geostress during the excavation of large underground caverns tends to bring about large deformation and failure problems of rock masses with interlayer staggered zones (ISZs), posing significant threats to the safety and stability of the underground cavern. Hence, for interlayer staggered zones with complex mechanical response behaviors, a series of conventional triaxial cyclic loading tests under different confining pressures were carried out. It can be seen from these results that the envelop curves of stress–strain relations were of obvious memory, but the peak deviator stress, internal friction angle, and cohesion were lower than those in monotonic loading. The phenomenon of volume expansion occurred in the whole process of cyclic loading and unloading, and the unloading dilatation seemed to be more sensitive to relatively low confining pressure. The volume expansion reached its highest value when the unloading stress level (i.e., the ratio of the stress ratio in the process of the cyclic test to the stress ratio when the ISZ comes to the failure point) increased to more or less 0.6∼0.8. Moreover, the changing trend of the average rebound modulus was humplike with the increase of unloading stress level, and the ratio of average rebound modulus to monotonic initial elastic modulus declined as a power function. Additionally, the validity of the unloading rebound modulus calculation by the Duncan-Chang model is proved. The analysis of energy consumption in plastic hysteresis loops indicates that the plastic hysteresis energy of the specimen in each cycle rose with the stress level’s increase. Further microscopic failure mechanism analysis shows that the previous research results are synthetically affected by factors including particle motion and breakage, initiation and propagation of original and new fractures, yield, and damage of interlayer staggered zones. This research provides a theoretical premise for exploring the cyclic unloading and reloading stress path influence on the failure of surrounding rock with ISZs, as well as for more reasonable mechanical parameter selection in deep underground excavations.

It is of crucial importance to develop an efficient numerical method to investigate the mechanism of grout diffusion and migration in fractured rock masses. However, most existing models only concentrate on the grout flow in a single fracture and most existing algorithms for large-scale fracture networks have high computational cost. A new dynamic diffusion and migration algorithm for grout was proposed and applied to the two-dimensional fracture network in this paper. Based on the geometric relationship between the fracture network nodes, an effective and feasible generation method of the connectivity matrix was proposed to realize the digitization of the topological structure of the fracture network. Finally, the Fracture Networks Grouting Diffusion Program (FNGDP) was developed to visualize the entire process of grout diffusion and migration in fracture networks. Compared with other algorithms, the proposed algorithm can realistically simulate the grouting process and greatly reduce computing time.

Classical mechanics theory is used to develop an analytical model for determining pile displacement due to temperature variations, in integral abutment bridges (IABs). The advantage of this model, as opposed to simple techniques proposed by AASHTO, is that it includes the forces that develop in the bridge due to soil pressure constraining the piles. A three-dimensional, nonlinear finite-element model (FEM) of the superstructure and substructure is developed to determine the displacement and cyclic behavior of piles. FEM is used to analyze the cyclic stress-strain behavior of piles and determine their inelastic deformation. Both the analytical model and FEM are used to calculate the displacements in piles for variety of bridge lengths under thermos-mechanical loading due to daily and seasonal temperature variations. Displacement calculations using the analytical model are then compared with the finite element and AASHTO results. The results show that although the new analytical model takes into account soil pressure on the piles, it does not include the soil pressure on the abutment. Therefore, the amount of deformation that FEM shows for expansion of the bridge is less than that determined by the analytical model. However, results of the analytical model are less than the AASHTO results. This shows that in conservative designs AASHTO can be used comfortably. If more accurate, less conservative design is desirable, the analytical model and FEM are proposed. FEM results show that maximum lateral displacement in (contraction) occurs during the winter. The displacement of piles in the summer and during high temperature times of the day shows a nonmonotonic trend with respect to depth providing buckling behavior in the piles. The piles’ displacement is completely monotonic during the winter and cold times of the night. For the bridge studied maximum stress occurs in the pile that is furthest from the center of the bridge. The cyclic stress-strain loop and inelastic deformation, both found from the FEM, are studied closely to identify the most likely location of a fatigue crack. Since plastic deformation occurs in piles, low cycle fatigue is expected. The most likely crack location is found in the flange of the pile right below the concrete abutment.

Within the framework of the limit equilibrium method of slices, a slope reliability analysis accounting for two-dimensional (2D) spatial variation requires a model to discretize a random field into a finite number of random variables. A careful review of the existing models has revealed that the models originally developed for homogeneous slopes suffer from certain shortcomings when applied to nonhomogeneous slopes, which have been taken care of in the refined models recently proposed by the authors. Further, on the two approaches followed in accounting for spatial variability, the paper examines the consequences of adopting the simplified approach based on a specific slip surface in place of the rigorous approach based on the probabilistic critical slip surface. Analyses of illustrative examples have revealed that an analysis based on a combination of an inappropriate discretization model and a simplified approach might result in errors as much as 65% on the nonconservative side. The paper also addresses the issue of obtaining solutions in slope situations in which site-specific values of the 2D scale of fluctuation are either not available or are different layerwise.

Stress state is a significant factor influencing the features of the soil–water retention curve (SWRC) under realistic in-situ conditions. The SWRC under different stress state conditions can be evaluated through experimental procedures and various constitutive models. Often, these models require experimental SWRC observations for at least two stress state conditions (i.e., a minimum of two reference SWRCs) to calibrate model parameters, which is difficult owing to the high time consumption associated with such experiments. In the present study, a simplified model is proposed by considering experimental SWRC observations for the single stress state condition to predict SWRC features for other stress state conditions in the gravimetric plane. An attempt has been made to extend the proposed model in the degree of the saturation plane using certain void ratio constitutive relations. The proposed model was validated against several SWRC experimental data sets available in the literature. Good agreement was found between the predicted and measured experimental results in the literature, with wide variations in the type of soils, stress conditions, and sample preparation methodologies. The proposed model is also capable of capturing the variation in key SWRC parameters considering the way the quantity of water is defined. The proposed method is quite simple and hence can be widely used for engineering applications.

The problem of dynamic response and momentary liquefaction of a transversely isotropic seabed subjected to water waves was treated analytically using a fully coupled dynamic model. The dynamic governing equations were first formulated as a set of sixth-order ordinary differential equations in terms of displacements of solid skeleton and excess pore pressure whose general solutions can be readily derived. Based on the appropriate boundary conditions, explicit solutions for soil displacements, effective stresses, and excess pore pressure as well as momentary liquefaction potential were subsequently determined in closed forms for the cases of water waves propagating over a transversely isotropic poroelastic seabed. The validity and accuracy of the proposed formulations and solutions were further verified through comparisons with existing analytical solutions that were special cases of the more general ones currently addressed. Some selected charts are presented and the effects of soil anisotropy on the calculated effective stresses and excess pore pressure as well as on the momentary liquefaction depth of a transversely isotropic saturated seabed are investigated and discussed.

A set of numerical experiments of simple shear tests of rockfill–structure interfaces were performed using the combined finite- and discrete-element method (FDEM). Each particle was modeled as a polyhedron to represent irregularly shaped rock grains, such as gravel and rockfills. The interfacial shear behavior was analyzed from the perspective of macroscopic mechanical responses and the evolution of contact networks and fabric structures. The macroscopic responses of the interfacial shearing of the rockfill–structure interfaces were typical of those observed in laboratory tests. A shear banding process was observed adjacent to the structure surface. The microscopic observations provided comprehensive information about the shear-induced phenomena in rockfill–structure interfaces.

A series of high-pressure compression tests with various stress paths under monotonic and cyclic loadings were performed to examine the compression and particle crushing characteristics of silica sand in a dense state. Different stress paths were particularly designated to individually investigate the influences of mean and shear stress on particle crushing. Test results show that the degree of particle crushing increases with the stress level and is markedly affected by the stress paths. For each compression test following a designated stress path, an increase in the cyclic loading number also enhances the degree of particle crushing. Particle morphology is affected by the accompanying occurrence and evolution of grain damage. The relative breakage expresses a linear relationship with the maximum volumetric strain during monotonic and repeated compression loadings. A good correlation between the relative breakage and plastic work per unit volume is obtained for silica sand at various mean stresses regardless of the stress history. However, this correlation is affected by cyclic loading number because of different crushing mechanisms. During the entire cyclic compression process, the increasing rate of relative breakage is lower than the plastic work increment for dense silica sand as the cyclic loading progresses.

Shape factors traditionally are used to relate the bearing capacity of square, rectangular, and/or circular footings to that of strip footings in geotechnical foundation designs, in order to take account of additional resistances developed in front of and behind strip footings. They traditionally are determined by experimental observations or deterministic analysis assuming uniform soil profiles. However, soils are spatially varying, and this variability can have a substantial influence on the bearing capacity of foundations resting on them. Therefore, the empirical shape factors used in foundation designs are quite uncertain, depending on the in situ soil variability. This paper investigated how soil spatial variability may affect the shape factors for the bearing capacity of square footings and the reliability of the traditionally determined shape factors. By quantifying the uncertainties involved, shape factors can be chosen based on site conditions and a target reliability. It was found that the traditional shape factor used in design has the lowest reliability for sites with intermediate soil spatial variability, and thus lower shape factors may be warranted to attain a required reliability in such cases.

The limit equilibrium method (LEM) and the finite-element method (FEM) commonly have been used in design to calculate the factors of safety (FS) against deep-seated failure of deep-mixed (DM) column-supported embankments over soft clays. Previous studies showed that the LEM with the conventional equivalent-area method (EAM) for column foundations yields higher FS than the three-dimensional (3D) FEM with individual columns. This study investigated the FS against deep-seated failure of embankments over deep-mixed columns using the 3D individual column method and the LEM with the conventional EAM. The roles of DM columns and soft clays in the stability of DM column-supported embankments were assessed by performing a weighted analysis and examining the stress states of the DM columns and the soft clay at failure. The results showed that the conventional EAM had a higher possibility of overestimating the FS against deep-seated failure of embankments over deep-mixed foundations than did the 3D FEM with individual columns. The conventional EAM overestimated the contributions of DM columns to the slope instability because some DM columns had not fully mobilized their shear strengths when the embankment failed in the 3D FEM, especially for soil and DM columns with a large strength difference and for DM columns with a large area replacement ratio. Load transfer almost disappeared at failure in the 3D model. Accordingly, a modified equivalent-area method was proposed and verified by comparing its results with those in the literature.

The shear modulus and damping ratio are important parameters for the design of structures subjected to dynamic loading and can be obtained by in situ and laboratory measurements. Previous research has lacked quantitative study of the effects of anisotropic consolidation, especially in extension mode, on the dynamic properties of granular soil. The objective of the current study was to evaluate the dynamic properties of sand-gravel mixtures for practical applications. To this end, resonant column, cyclic triaxial, and S-wave velocity measurements under anisotropic confining conditions were conducted. The influence of mean effective consolidation stress, consolidation stress ratio under constant and variable mean effective stresses, and gravel content on the maximum shear modulus $G_{\max }$, $G/G_{\max }\text{-}\gamma$ and $D\text{-}\gamma$ curves are discussed. Simple formulations are presented to predict $G_{\max }$ and the reference strain (${\gamma }_r$) of sand-gravel mixtures using parameters that are easy to obtain from test data. A modified empirical model is proposed based on the test results to estimate the shear modulus degradation and damping ratio. The modified model is validated using experimental data from previous studies. The results indicate that the proposed empirical model is capable of evaluating the shear modulus and damping ratio of granular soil.

The multiple stress creep recovery (MSCR) test has been extensively recognized as a more effective method for characterizing the rutting resistance of asphalt binders than the traditional linear viscoelastic (LVE) theory–based Superpave performance grading (PG) test that determines the rutting parameter. However, recent studies have shown that the MSCR test has a major limitation in that the 9-s recovery period in each cycle may not allow complete recovery of the delayed elasticity, particularly for modified binders, which implies that the definitions of the parameters from the MSCR test, e.g., the nonrecoverable compliance $J_{\mathrm{nr}}$, are not the strictest ones. To accurately separate and obtain the actual irrecoverable and recoverable responses of binders from the MSCR test, this study developed a new procedure that uses the full Schapery nonlinear viscoelastic (NLVE) model and the LVE properties from the frequency sweep test. The results showed that the presented approach overcomes the deficiencies of existing methods, and can accurately and effectively characterize the NLVE and irrecoverable behaviors of the binders, regardless of whether they were polymer-modified or neat, and can guarantee the consistency of the material information from the traditional PG test and the MSCR test. Because of these advantages, the procedure provides a potential approach for further analyzing and modeling the rutting behavior of the corresponding asphalt concrete.

An analytical model was developed to simulate migration of methane (${\mathrm{CH}}_4$), oxygen (${\mathrm{O}}_2$), carbon dioxide (${\mathrm{CO}}_2$), and nitrogen (${\mathrm{N}}_2$) through a four-layer landfill biocover, which can account for the four-layer structure and the diffusion-advection-${\mathrm{CH}}_4$ oxidation processes. The model was effectively validated against experimental data first. The influences of several important factors including pressure difference, degree of saturation, ${\mathrm{CH}}_4$ oxidation, and layer thickness were then investigated. The water accumulating at the capillary layer benefits mitigating ${\mathrm{CH}}_4$ emission. But increasing the degree of saturation of the top layer enhances ${\mathrm{CH}}_4$ emission. The ${\mathrm{CH}}_4$ emission rate is controlled by both diffusion and advection in the top layer but mainly controlled by advection in the capillary layer. The ${\mathrm{CH}}_4$ emission rate reaches its minimum when the top layer thickness is close to that of the aerobic zone. Increasing the capillary-layer thickness can reduce ${\mathrm{CH}}_4$ emission more effectively than increasing the total biocover thickness. A capillary layer with a thickness of 0.55 m can control the ${\mathrm{CH}}_4$ emission rate below $0.45\mathrm{mol}/{\mathrm{m}}^2/\mathrm{day}$ under a pressure difference of 500 Pa.

In situ stress is a significant characteristic of underground rock masses. This work extended the time-domain recursive method (TDRM) to study oblique wave attenuation across an in situ stressed joint wherein the normal and shear deformation behaviors were both treated nonlinearly. Employing the Barton–Bandis (B-B) and hyperbolic nonlinear (HN) slip models, equations were established for wave propagation across a rock mass under a combination of gravitational and tectonic stress. Then, the stress and displacement in the normal and shear directions were calculated under different in situ stresses for P- and S-wave incidence. The waveforms of the HN slip model and the Coulomb slip model were compared to investigate the differences therein and verify the wave propagation equation. Parametric studies were conducted to elucidate the influences of in situ stress, lateral pressure coefficient, angle of incidence, and amplitude of the incident wave. The results showed that the HN model depends on the stress history and shear stiffness degradation. The effect of the in situ stress on wave propagation depends not only on the gravitational and tectonic stresses but also on the direction of the particle vibration of the incident wave.

The mechanical and hydraulic properties of granular materials are fundamentally affected by the grain size and shape. Three samples of uniformly graded quartz sand with different size ranges were subjected to one-dimensional compression tests up to 40 MPa to fracture the sand into fragments with a variety of sizes and shapes. X-ray computed tomography was used to obtain the morphology of the crushed sand at a resolution of 2.8 μm. A practical divide and stitch method was proposed and implemented to automatically separate and extract individual grains for morphological analysis. This method can reduce the misidentification of grains and voids. Scans of 5,481 grains were used to quantify the three-dimensional morphological properties of grains of different sizes and shapes. The shape descriptors of elongation, flatness, and sphericity were the best way to describe the grain shape. The intermediate Feret diameter was the best parameter for characterizing the grain size. The smaller fragments from the crushed sand were more elongated and had higher flatness and convexity. The distributions of elongation, flatness, sphericity, and convexity for grains in different size ranges followed a normal distribution. The standard deviation in the grain shape descriptors increased for the small grain sizes. The volume and surface area of the grains can be predicted with high confidence using elongation, flatness, and intermediate Feret diameter. Convexity needs to be used along with elongation and flatness to estimate sphericity reliably.

Some numerical models treat masses of rock as assemblages of isolated blocks, whereas others treat them as continuous material. It needs to be determined at what level a rock is cut into assemblages of discrete blocks by fractures. This paper used a parameter $B$ to measure the degree to which rocks form an assemblage of blocks; $B$ is a dimensionless number in the range $0.0<B<1.0$ and is defined as the ratio of the aggregated volume of individual blocks in the investigated domain to the total volume of the rock mass in the investigated domain. The quantitative description scheme for fracture spacing and persistence suggested by the International Society for Rock Mechanics (ISRM) was used to construct different types of fractured rocks to conduct investigations into blockiness. Seventy-seven different types of fracture networks were studied. The fractures investigated covered all the fracture spacing and persistence ratings suggested by the ISRM. Based on the blockiness of the 77 samples, an analytical function was established to describe the relationship between the blockiness and the fracture spacing ($S$) and fracture disc diameter ($D$). The resulting function is an S-shaped curve.

Three-dimensional (3D) complete nonlinear methods for examining soil–building interaction based on an input seismic wavefield were developed. A seismic wavefield means seismic waves propagating in a 3D medium. Vertical ground motions and the material nonlinearity of the superstructure and the piles were incorporated into earlier methods. Consequently, employing a three-component input wavefield including surface waves, the methods are able to treat nonlinear behavior of the superstructure and the piles in the cases of soils with nonlinear and liquefaction behavior. The feasibility of the methods was demonstrated using a midrise RC building in the lakebed zone of Mexico City and a midrise RC building and a wood building in the reclaimed zone of Tokyo Bay. The response of a midrise RC building of Tokyo was displayed. The methods provide reasonable nonlinear building performance. Building responses became excessively large following extremely large increases in the amplitudes of surface waves in liquefied soils, thereby successfully indicating that Japanese RC building damage concentrates in the first story.

Understanding the structural behavior of layered asphalt pavements subjected to dynamic moving wheel loads is a crucial requirement for the future design of more-durable pavement structures. Therefore, to accurately evaluate the dynamic response of an instrumented semi-rigid base asphalt pavement under full-scale moving heavy vehicular loading, this study established a full-scale three-dimensional viscoelastic finite element model. Sinotruck HOWO A7 $6\times 4$ dump truck moving wheel loads and associated contact stresses effect on the pavement structure were implemented in the implicit dynamic analysis. The dynamic properties of the asphalt concrete were incorporated in Abaqus through a Prony–Dirichlet series. The rationality and validity of the developed model were successfully verified by field data collected from a Rizhan–LanKao highway pavement test section in Shandong province, China. The pavement dynamic response computed at different depths under the truck dual tires and at a different lateral position in the mid-depth of asphalt concrete middle course were analyzed. Results indicated that both tensile and compressive three-directional dynamic strain, stress coexist in the pavement structure. In addition, an alternating change was found between negative and positive dynamic shear stress and strain in the structure. Finally, this study revealed that the peak value of the dynamic strain–stress in vertical, transverse, and longitudinal directions, as well as the shearing strain–stress response of the pavement structure, are affected not only by the lateral distribution of the analysis points but also according to depth.

In this paper the influence of grain fragmentation on the change of the grain size distribution and an additional compaction of a cohesionless granular material was modeled in a simplified manner by introducing the mean grain diameter and the solid hardness as state variables into an extended micropolar hypoplastic model. The solid hardness was defined in the sense of a continuum description and was a key parameter for modeling the incremental stiffness. The reduction of the mean grain diameter and the solid hardness caused by grain fragmentation was described by evolution equations taking into account an increase of the mean pressure and a change of the stress deviator. Because in the extended model the critical void ratio also depended on the evolution of the solid hardness, a reduction of the critical void ratio caused by grain fragmentation also was taken into account. To investigate the effect of grain fragmentation on the mechanical response, numerical simulations of plane strain compression tests were carried out for two different types of tests. A biaxial compression test under unconstrained lateral deformation and a biaxial test of the Hambly type were simulated using the finite-element method. Particular attention was paid to the influence of the initial void ratio and the type of the lateral boundary conditions on the interaction between the evolution of strain localization and the reduction of the mean grain diameter. The numerical simulations showed that the reduction of the mean grain diameter was pronounced in zones of shear strain localization and it was larger for the initially dense specimen. The evolution of patterns of strain localization and of zones of intense reduction of the mean grain diameter strongly depended on the boundary condition of the test type.

Nowadays, micropiles, due to their capability to sustain high loads in a soft cohesive soil, are drawing attention from researchers, geotechnical engineers, and builders. However, the load-carrying capacity of a micropile group in soft cohesive soil is not readily available. This paper describes an investigation of support vector machine (SVM) regression for assessment of micropile group capacity in soft clayey soil considering the complex interaction between the soil and the micropiles and the uncertainty involved in the analysis. A total of 54 large-scale static vertical micropile load tests were conducted in a test pit, and from the load-settlement graphs plotted for these tests, a database of 376 data points was obtained that was used to develop the SVM model. The performance of the SVM model with three different kernel functions was evaluated The results of the SVM models were compared with those of artificial neural network models developed with three different types of algorithms. To determine the relative influence of the different input variables on the load-carrying capacity of micropile groups, a sensitivity analysis was also performed. An empirical equation was developed with the best-fit model for practical application. The developed equation was validated with a set of experimental data not used for generating the empirical equation.

For geotechnical systems involving complex behaviors and significant uncertainties, metamodeling-based reliability methods based on fixed designs of experiment (passive metamodeling methods) are frequently applied. However, because of the passive nature of these methods, they do not guarantee accurate probability estimates. This issue also persists in estimates obtained from active metamodeling methods (metamodeling methods that update the design of experiment iteratively) if a global stopping criterion or a nonoptimal learning function is used for the type of problem. This study highlights the importance of addressing these issues by investigating an example of failure analysis of soil slopes and concludes that the stopping criteria for development and refinement of metamodels need to be objective and locally defined with respect to the limit state function (LSF) and with a direct link to the accuracy of the reliability estimates. To address these challenges, this study established an effective sampling region that optimally ignores candidate design samples with weak probability densities. This enabled the development of an effective learning function that facilitates the active learning process. Moreover, an analytical upper bound for the error in failure probability estimation, proposed by the authors, was adopted here to arrive at a local and objective stopping criterion. This method was applied on two soil slopes, the stability of which was evaluated by the strength reduction method (SRM) in FLAC3D. The results highlight that passive and active methods with global stopping criteria cannot guarantee an accurate estimate of the failure probability. Furthermore, the developed method can considerably reduce the computational demands while achieving accurate estimates of failure probabilities of soil slopes.

The stability of borehole is a major concern in petroleum and geotechnical engineering. Subsurface fossil fuel and thermal energy extraction, deep geologic carbon/energy storage, and waste disposal require sophisticated borehole modeling. In many instances in deep well drilling, rock exhibits a plastic behavior rather than a pure linear elastic behavior. Rock is a porous material consisting of a compressible solid matrix and number of compressible fluids occupying the pore space, so numerical analysis of complex borehole problems based on nonlinear poromechanics is indispensable. In computer methods for nonlinear poromechanics, it is expected that the tangent stiffness method is more efficient than the constant stiffness method because the number of iterations can be reduced; however, the speculation has not been corroborated, especially when applied in borehole engineering. To investigate the computational efficiency of the two methods, fully coupled poroelastoplastic borehole modeling was implemented by both the tangent stiffness and initial (or constant) stiffness methods. Results showed that the two calculation methods are consistent, and the computational performance of the tangent stiffness method is superior to the initial stiffness method based on borehole modeling, reflected in the significantly reduced number of iterations and total running time required.

A series of laboratory experiments were carried out to study the tangential stress concentration–induced spalling failure process of rock in an arch-shaped tunnel model under plane-strain loading condition by considering different geological conditions, i.e., a tunnel with and without a fracture nearby. Different fracture properties, i.e., open fracture and fracture with different infilling materials around the tunnel, were designed to study their influence on the spalling behavior. Digital image correlation (DIC) and acoustic emission (AE) were combined to track the spalling initiation and formation, which is characterized by the deformation field and energy release rate evolution. Spalling at two sidewalls of the tunnel without a fracture under concentrated tangential stress, and formation of various thin slabs and detachment from the free boundary due to the initiation and propagation of dilatant cracks were well reflected. Asymmetrical spalling failure was observed due to the existence of the fracture around the tunnel. It was found that the open fracture makes the spalling more concentrated and leads to larger failure extent and more intensity than the tunnel with a filled fracture.

The results of a series of drained and undrained triaxial compression tests terminated at various axial strains were reported to show the gradual accumulation process of particle breakage of a carbonate sand during triaxial compression. A breakage model, which relates the particle breakage rate to the accumulated amount of particle breakage and current effective confining pressure, was established based on the drained test results. The effectiveness of the breakage model was validated by successful simulation of the undrained test results using the same parameters calibrated from the drained tests. Incorporating the breakage model into the critical state framework, a constitutive model for the carbonate sand considering particle breakage was established through a critical state surface in the space of void ratio, mean effective stress, and relative breakage, and a variable critical state stress ratio decreasing with increasing breakage. The comparison of the test results and the model simulations with and without breakage revealed the way in which the evolution of particle breakage affects the deformation behavior.

The yield criterion of rock is significant for the identification of the whole failure process and the stability analysis of rock engineering. Studies of yield criteria from energy aspects are critical but rare. This paper investigated the yield criterion using strain energy and a modified compounded mobilized planes (CMP) model. The yield strain energy and strength criterion were formulated with different combinations of stress variables. Based on conventional triaxial and true triaxial tests, the evolution laws of mechanical parameters, including elastic parameters and strength parameter, were quantitatively determined. Accordingly, a new parameter correlation model, intermediate principal stress effect, and prerequisite for convex yield surface were investigated with theoretical and experimental approaches, respectively. With respect to previous criteria, the studied criterion has some advantages. Firstly, parameter correlations can be characterized with this criterion. Secondly, the shape of the yield surface is criterion-dependent and relies on rock properties, and can be applied to wide range of rocks. Thirdly, the estimation of yield stress is quasi-independent of the sample variability, which resulted in good agreement with test data. Fourthly, the criterion can be transformed into some classic criteria widely used in civil engineering. The criterion in this study offers an alternative viewpoint. In addition, it has high calculation precision and wide application for varied rocklike geomaterials.

Controlling rock mass uplifting is of great importance when grouting in large opening fracture with flowing groundwater. This paper investigated the basic mechanism of overburden stratum uplift. The ideal fluid assumption was used to analyze the flowing regularity of the grout spreading against flowing groundwater and fluid pressure distribution in a single flat fracture grouting work. The calculated fluid pressure was modified according to the results of single flat fracture grouting simulation test in a prior work to estimate the actual uplift force acting on fracture walls induced by grout pressure. Results showed that the deviation from the actual value induced by ideal fluid assumption can be omitted in the calculation of grout velocity and spreading distance. On the other hand, the deviation for pressure distribution is rather large, and should be modified according to the real-time monitoring of the injection pressure in the actual grouting project. According to the requirement for sealing groundwater, the maximum grouting pressure is determined, and a criterion for risk assessment on overburden stratum uplifting is established.