International Journal of Geomechanics

A new block-classification method for tunnel construction using a tunnel-boring machine (TBM) to capture the geometrical and mechanical transformation of rock blocks in the course of TBM excavation is proposed in this paper. The machine–block interaction is interpreted by dividing the joint blocks into blocks influenced by TBM excavation and blocks uninfluenced by TBM excavation. The influenced blocks are categorized further as contacting or noncontacting blocks according to whether they are in contact with the TBM. The contacting blocks include the front block, the corner block, and the rear block, based on the spatial location of blocks with respect to the cutterhead. Different types of blocks have distinct kinematic and mechanical characteristics. The sizes and shapes evolve, and the categories may be changed for rock blocks during excavation. The identification algorithms for influenced blocks and three types of contacting blocks are presented. Finally, a simple example considering a double-shield TBM tunnel excavation is used to illustrate the effectiveness of the new block-classification approach to guide TBM tunneling. The new classification approach will be helpful in evaluating the block removability and the possibility of cutterhead clogging and to shield blockage during tunneling with a TBM.

A displacement-based seismic discontinuous deformation analysis (DDA) considers the influence of an earthquake by applying a time-dependent displacement constraint to simulate time-dependent ground movement of the base rock. However, unexpected variations of the base block stress and the block area in a seismic DDA may affect the block contacts with another block. This study theoretically clarifies the mechanism that causes unwanted base block distortion in a seismic DDA. A new geometric restriction is proposed for the assignment of displacement–constraint points to simulate the ground movement of two-dimensional (2D) and three-dimensional (3D) convex and concave blocks without changing the DDA algorithm. Additionally, the Daguangbao rock avalanche triggered by the Wenchuan earthquake in China is considered as a case study to demonstrate the capability of the new geometric restriction in a DDA to solve practical problems.

The fault cutting algorithm is important when applying the three-dimensional numerical manifold method to engineering simulation. This paper presents a primary approach to the fault cutting algorithm, including data structures, fault cutting procedures, and some basic computing algorithms. First, the data structures of the physical elements and mathematical covers are proposed as single linked lists and linked list arrays, respectively. This reduces the complexity of the algorithm and increases the efficiency when connecting physical elements to covers. Second, a strategy of recording cutting traces between every two faults to ensure that the model agrees with the actual situation was proposed. This strategy also reduces the complexity and improves the efficiency. Third, the mathematical covers and physical elements are cut with all faults independently to process complete cutting instances in a multiblock form and incomplete cutting instances without forming any new irrational block. Finally, four cutting examples are presented that demonstrate that the proposed fault cutting algorithm is correct and useful.

A beam-element-based rock bolt model is proposed in this paper. The proposed model can not only simulate the compression and tension deformations of bolts in the rock block but also capture the interaction between the bolt and the joint. The antitension, antishear, and antirotation of bolts near the joint and the hardening characteristics of bolts after the plastic yielding can be comprehensively reflected using the proposed model. The rock bolt model has been incorporated into the original numerical manifold method (NMM) procedure developed for realistic applications. In the improved NMM procedure, the bolt can be input as the physical mesh, the layout of which is not correlated with the mathematical cover. Hence, the preprocess is simplified, and numerical simulation of a large number of bolts can be easily carried out. The results of this improved procedure for bolt modeling were verified with a direct shear test of an anchored joint. Finally, the procedure was applied to evaluate the reinforcement effect of bolts in the underground powerhouse of the Shuibuya hydropower station. The results show that the deformation behavior of the anchored rock mass and the reinforcement effect of bolts can be well captured by the bolt model.

A temporal coupled explicit–implicit time integration algorithm is proposed to improve the computational efficiency of the numerical manifold method (NMM) for seismic stability analysis of rock slope. It includes a coupled time integration scheme, a phase transfer criterion, and an associated contact algorithm. To calibrate the proposed algorithm, a block sliding along a slope under seismic excitation and a block rocking under half-sine pulse shaking are simulated. The traditional limit equilibrium method (LEM) for slope stability analysis determines the factor of safety (FoS) without considering the time-dependent effect. The developed algorithm is able to simulate jointed rock slope seismic stability taking advantage of the NMM for continuous and discontinuous deformation analysis. An open-pit mine slope excited by the El Centro earthquake wave is studied. The simulated results are in good agreement with the results based on the traditional NMM, whereas the computational efficiency is improved significantly. The proposed coupled time integration algorithm has the potential to be applied to larger engineering problems to save computational cost.

Failures of metro tunnels that pass obliquely through ground fissures at low angles are a common problem; however, their mechanism is unknown. In the city of Xi’an, China, Line No. 3 of the Xi’an Metro intersects ground fissures at a low angle (<25°) in certain zones. In this study, particle flow numerical analysis and physical model tests were used to investigate ground-surface deformation, structural distortions, and failure characteristics caused by ground fissures. Tests revealed an integrated bend-shear-torsion failure mode of any tunnel that entered a ground fissure obliquely at an angle of 20° or less, under the action of activities associated with a ground fissure. The tunnel structure indicated damage characterized by long longitudinal cracks and multiple groups of subparallel vertical cracks. The range in failure of the tunnel was up to 3.5 times the tunnel diameter on the hanging-wall side and up to 4.5 times the tunnel diameter on the foot wall. When metro tunnels intersect ground fissures at low angles, traditional tunnel designs do not meet minimum safety standards. It is therefore necessary to explore alternative metro tunnel designs in fissure-prone areas.

This paper develops a novel empirical strength criterion and proposes a manifold method for fracture initiation and propagation. First, to investigate the influencing factors of fractured rock mass strength, a set of uniaxial and biaxial compression tests were performed on gypsum specimens. According to the experimental results, rock mass strength is attributable to nonlinear relationships with fracture inclination angle, length, and lateral pressure. Then, on the basis of strength theory and tests, an improved empirical strength criterion, which can describe the multi-influence of fracture inclination angle, fragmentation degree, and lateral pressure on strength of the rock mass and the path of fracture propagation, was established. Moreover, the critical conditions of tensile and shear fracture for fracture propagation are proposed and used with a numerical manifold method to simulate fracture propagation. Furthermore, in the modeling, the manifold element is regarded as the basic failure element, and the failure angle is used to determine propagation direction. The results of the fracture-initiation strength and the propagation path with traditional Mohr-Coulomb criterion and the improved empirical strength criterion are compared to validate the proposed method.

The discontinuous deformation analysis (DDA) method calculates large deformations and discontinuous problems using time-step solving and provides an effective tool for analyzing the seismic response of rock mass engineering. In this paper, extensions of the DDA method to simulate the seismic response of a large rock cavern complex are carried out. First, applicability of the existing seismic input methods, including the multiblock Newmark method, large mass method, and large stiffness method, are discussed. Second, considering the characteristics of the seismic response of a large rock cavern complex, a new seismic DDA model that includes a coupling model and a force-input method is presented. Last, the extended DDA method is used for a case study. Simulations of the quasi-static and seismic dynamic stages for the large rock cavern complex of the Dagangshan hydropower station in southwest China are carried out. Considering the stress and displacement distributions in the quasi-static stage, the most unfavorable movable blocks are found. In the seismic dynamic stage, serious damage to the main machine building and local damage of the downstream sidewall of the main transformer chamber are observed, and the seismic response of the large rock cavern complex can be visually divided into four phases, which show that failures of the most unfavorable movable blocks are an early sign of collapse of a rock cavern complex.

Compared with two-dimensional (2D) contact cases, three-dimensional (3D) contact problems are more complicated in both contact geometry representation and contact detection. The entrance block theory proposed by Shi lays the foundation for solving contact problems in a uniform format. This paper presents a new contact detection approach for 3D polyhedral blocks with the use of entrance block theory. In this approach, contacts between 3D polyhedra were classified into three categories: finite-contact covers (face to face, edge to face, and parallel edge to edge), single-contact covers (vertex to face, crossing edge to edge, vertex to edge, and vertex to vertex), and basic-contact covers (vertex to face and crossing edge to edge). A finite-contact cover consists of several single-contact covers, and all single-contact covers can be identified as basic-contact covers. Thus, the contact detection process can be fulfilled in three phases: a rough search phase to form a potential contacting block list for all blocks, a delicate search phase to detect the four single-contact covers, and an identification phase to identify basic-contact covers from all single-contact covers. Because contacts happen on boundaries of blocks, which can be regarded as a union of boundaries of 3D block angles, the delicate search can be fulfilled through detection between boundaries of 3D block angles to increase its efficiency. After contact detection, a list of potential contact pairs based on the three contact categories was formed and solved based on two basic-contact covers (i.e., vertex-to-face and crossing edge-to-edge contact covers). The half-edge data structure was applied to represent angles, edges, and polygons in polyhedra. The contact detection algorithm was fulfilled in the framework of 3D discontinuous deformation analysis (DDA), using the object-oriented programming method. In this paper, examples are provided to verify the accuracy of the proposed algorithm in treating vertex-to-vertex, vertex-to-edge, parallel edge-to-edge, edge-to-face, and face-to-face contact types as well as its robustness in solving contacts of a large number of blocks.

The performance of discontinuous deformation analysis (DDA) needs to be improved for large-scale analysis. In this study, the contact detection and open-close iteration, as the bottlenecks of DDA computing, are reimplemented on graphics processing units (GPUs). For contact detection, the proposed parallel method accelerates DDA computing by maintaining a high loading balance and data reuse ratio on the GPU. The open-close iteration is divided into two parts, simultaneous equations solver and interpenetration checker. For the simultaneous equations solver, both the parallel Jacobi method and the block Jacobi preconditioned conjugate gradient (BJPCG) methods are implemented on the GPU to substitute the original successive overrelaxation (SOR) method. The parallel interpenetration checker is improved by optimizing conditional branches on the GPU. Two applications of the new parallel methods are introduced. The results showed that the broad and narrow phases of contact detection showed 18 and 5 times speedup, respectively. The parallel BJPCG simultaneous equations solver showed 16 times speedup, and the parallel interpenetration checker showed 2 times speedup. The total performance of DDA is improved about 2 and 10 times, respectively, using the proposed methods.

This paper presents a contact parameter estimation method for collision modeling using discontinuous deformation analysis (DDA). Most DDA codes and discrete element method (DEM) codes use the viscoelastic contact model for contact-stress calculation. The contact parameters of the viscoelastic contact model, such as normal stiffness and damping constant, affect the computation results observably. Although the DDA method has been proposed for more than 20 years, the contact parameters in DDA modeling are still difficult to determine. In collision dynamics, the coefficient of restitution (COR) is considered the critical parameter for describing the changes of motion state after collision between two objects. In the proposed method, the normal COR is used for evaluating calculation results of rockfall modeling with three-dimensional DDA. The normal COR of the two-object model is obtained by tests or empirical methods. The relation curve of contact parameters and the normal COR is generated on the basis of a series of numerical computations according to the tests. Then, the reasonable combination of normal stiffness and damping constant can be calculated by matching the normal COR on this curve and used in other similar computations to obtain more practical results. An example based on laboratory tests is reported to validate the method.

The numerical manifold method (NMM) is suitable for the solution of both continuous and discontinuous problems in geotechnical engineering. In the conventional NMM, the contact between blocks is treated with the open-close iteration, which needs to fix or remove spurious springs between two blocks in contact and to assume properly the normal stiffness and the tangential stiffness (the penalty parameters). Unreasonable values of stiffness would result in numerical problems. To avoid the penalty parameters, contacts are treated in a direct way in which contact forces are primal variables. Numerical examples have confirmed the correctness and feasibility of the proposed procedure.

Surface roughness is one of the most important parameters that have significant influence on the mechanical and hydraulic characteristics of rock joints. To investigate the evolution of surface roughness under normal and shear loads, direct shear tests and numerical modeling based on the discrete-element method (DEM) were performed; bright area percentage (BAP), which places emphasis on the contact areas, was used as an index to describe the roughness. The results demonstrate that the surface roughness of rock joints decreased gradually as the shear displacement increased, and then roughness experienced a significant reduction in the residual stage and remained constant. Furthermore, the evolution of surface roughness was found to depend on the normal stress and shearing direction. Reduction in the degree of joint roughness with high normal loads was lighter than that with lower normal loads, and roughness varied with shear directions. The numerical simulation method proposed in this study has the potential to track the changes in roughness during the shearing process, and a good match was achieved with the experimental results.

A particle-based numerical manifold method (PNMM) is developed to investigate rock fracturing behavior under dynamic loading. The basic idea of PNMM is to represent the microstructure of rock with a group of particles and to simulate the macroscopic behavior of rock masses through polygonal elements, which is performed by a dual-level discretization system. The first discretization is in the manner of FEM, which reduces the infinite degrees of freedom (DOF) of a continuum to the finite DOF of polygonal elements. However, the DOF of the model are not further affected by the latter discretization. The behaviors of internal particles are obtained from the mechanical fields of their governing elements. A dual-layer-cover system, i.e., the mathematical cover and the physical cover, is adopted in PNMM. Fracture initiation and propagation at a macroscopic level are represented as the coalescence of microcracks induced at the microscale level between particles. The Johnson-Holmquist-Beissel (JHB) model is incorporated into PNMM to simulate a borehole blasting under dynamic loading conditions. Numerical simulations show a good agreement with experimental and numerical results in the literature.

Rock cutting and rock penetration are typical problems in civil, mining, petroleum, and geothermal engineering disciplines. They involve dynamic fracturing and fragmentation of rock, high-speed movements of a cutter/impactor, and complex dynamic contacts between the cutter/impactor and the rock. In this study a new three-dimensional (3D) coupled approach is developed to address these problems. The distinct lattice spring model (DLSM) is used to simulate the dynamic fracturing process of the rock, and the discontinuous deformation analysis (DDA) is adopted to model the high-speed motion of the cutter/impactor. An explicit-implicit coupling scheme is developed to bridge DLSM and DDA. Moreover, to take account of interaction between DLSM and DDA, a 3D simplex sphere-to-block contact method is introduced. Finally, a number of numerical examples are conducted to verify the implementation of the coupled approach and its ability to model rock cutting and rock penetration problems.

Three-dimensional (3D) discontinuous deformation analysis (DDA) is very suitable for simulating large-displacement behavior of rock masses. One fundamental issue commonly encountered in 3D DDA is 3D friction problems. In this paper, a friction contact model based on 3D spherical DDA (SDDA) and the determination method of friction force direction is proposed for modeling 3D friction problems. Simulation results of three verification examples with available analytical solutions demonstrate the correctness of the friction contact model in 3D SDDA. Meanwhile, the simulation result of one application example, namely, a 3D-sphere natural-accumulation simulation, indicates that the friction problems of a 3D-sphere system can be modeled well by the proposed friction contact model. This work is helpful for solving 3D friction problems in discrete blocky systems.

The discontinuous deformation and displacement (DDD) analysis method, a combination of the realistic failure-process analysis (RFPA) and discontinuous deformation analysis (DDA) methods, offers an appropriate approach for whole rock failure-process analysis involving both the small deformation and large displacement stages. A high rock-slope slide at the Alpetto Mine in Cesana Brianza, Italy, was simulated with the DDD method, and the results are consistent with site observations and previous numerical results, which validates the DDD code for this kind of geotechnical problem. Moreover, this study verified the two main advantages of the DDD method, i.e., the critical failure surface can be obtained directly without any assumptions with the RFPA module before using the DDA module, and computing efficiency is improved significantly because the large displacement elements are the only elements that need to be calculated by the DDA module. The DDD method has proved to be an effective and efficient approach for engineers in the field of rock slopes, and it shows huge potential in geotechnical engineering.

This paper contains a summary of the developments and applications of the two-dimensional discontinuous deformation analysis (DDA2D) method regarding the modeling of rock-mass dynamics problems. Reviews on the control parameter value selections in DDA2D calculations and the developments and applications of the DDA2D regarding the analysis of rock slope failures, landslides, rockfall, some earthquake-related problems, and so forth, are performed. Research on the DDA2D for three basic rock-mass dynamics problems, such as block dynamic sliding, stress wave propagation, and dynamic fracturing, are specially stated. The modeling of rock blasting, a typical exact rock dynamics problem, is selected as a representative application example of the DDA method to be presented. Generally, the DDA2D has shown to be a powerful numerical method for the modeling of rock-mass dynamics. However, one should pay enough attention to the value selections of those important user-supplied control parameters, as well as to other important factors, such as block size and boundary conditions, for rock dynamics simulations, which have been specially addressed in the paper.

Coarse-grained materials (CGMs), including gravel, ballast, and rockfill material, exhibit a complicated stress-strain-volume change behavior, which is state dependent and influenced by considerable particle breakage even under relatively low pressure. A generalized plasticity model with a multiaxial formulation is developed for CGMs based on the critical state concept. The effect of particle breakage on their critical state behavior, including the nonlinear variation of both shear strength and void ratio with the mean effective stress, is fully incorporated with an implicit form in the current model. Two state functions and the corresponding virtual stress ratios are proposed to construct the new formulation of dilatancy, plastic flow, loading direction, and plastic modulus in the present model. The numerical analyses are performed for a series of true triaxial tests on CGMs, and model predictions are in good agreement with experimental results of true triaxial tests over a wide range of pressures. In summary, the proposed model is capable of accurately characterizing the highly nonlinear shear behavior due to particle breakage of CGMs, particularly including their strain softening/hardening and plastic dilation/contraction in various load paths.

Stone columns are a popular form of ground improvement that can be applied to a variety of foundation solutions involving soft soil deposits. Many design methods are based on an assumption that columns with a length-to-diameter ratio greater than 4 bulge uniformly along their length. This mode of deformation is not valid for small groups of columns in which interaction between individual columns and the footing gives rise to more complex behavior. The deformational behavior of stone columns at serviceability limit state is of utmost importance, because settlement rather than bearing capacity criteria are generally more onerous in soft soils. The results of some high-quality laboratory studies have been informative in this respect, but the extrapolation of results from small-scale tests comes with the caveats associated with single-gravity laboratory testing. The FEM, in combination with advanced constitutive models, can provide a link between the deformational behavior and settlement performance of discrete column groups at working stress levels. A series of analyses was conducted to examine the influence of key design parameters such as column length, spacing, and the number of columns. The influence of a stiff crust was also examined, because the reference soil profile adopted for these analyses was that of the well-characterized Bothkennar test site. The following three modes of deformation were identified by examining the distribution of stress and strain within columns and the surrounding soil: individual punching, block punching, and bulging. Individual and block punching developed in short or closely spaced columns, whereas block punching was more prevalent in larger groups. Bulging develops in long, widely spaced columns and generally occurs at the point of lowest lateral restraint. In addition, novel parameters referred to as compression and punching ratios were developed to validate the in-depth analysis and identify the principal design parameters that influence the behavior of small groups of stone columns. The results indicate that the mode of deformation is governed by column spacing and length rather than the number of columns. This finding is important, because it indicates that settlement design methods that are developed for large groups of columns are applicable to discrete groups at similar spacings and lengths. It was also observed that the influence of the stiff crust forces bulging to occur deeper and might have led authors in the past to suggest the existence of a critical length.

A plasticine material exhibits the characterized viscous stress–strain behavior with some similarity to the behavior of clayey soils. This paper presents a series of experimental tests, which include oedometer tests, isotropic creep tests, and triaxial multistrain rate compression tests, on a plasticine material. The test study focuses on effects of time and strain rate on viscous stress–strain behavior of the plasticine material under one-dimensional (1D) straining, isotropic stressing, and triaxial compression conditions. Values of compression index (C_cε), rebounding index (C_rε), and creep coefficient (C_αε) are obtained from the 1D straining and 1D stressing test data. The plasticine material has no primary consolidation period, and creep occurs from the beginning. Values of C_cε, C_rε, and C_αε are smaller than those of the soft clays. The triaxial multistrain rate compression test data show that the stress–strain behavior of the plasticine depends on the strain rates and the confining pressures. A parameter of ${\rho }_{0.01}$ is adopted to evaluate the strain-rate effects. The strain-rate effects on the stress–strain behavior of the plasticine material are obvious and significant. The values of ${\rho }_{0.01}$ are larger than those of clays. Both friction angle and cohesion of the plasticine increase with strain rate. This is different from the friction angle and cohesion at the critical state for all soils. The friction angle of the plasticine is from 2.57° at a strain rate of 0.01%/min to 3.21° at a strain rate of 1%/min, which is much smaller than that of all clays. With the help of a scanning electron microscope, the microstructures of this plasticine material before and after oedometer and isotropic creep tests are visualized and compared. The compression of the plasticine material is mainly due to the irrecoverable porosity decrease of the material and the structural compression.

An experimental study on the load-carrying mechanism of vertical plate anchors is presented and discussed. It was found that, with a shallow anchor, the rupture surface reached the ground surface, leading to a general shear failure, whereas with deeper embedment, the rupture surface was localized around the anchor. Anchors placed close to the ground surface failed in linear rupture but, when embedded within the failure mechanism, were very close to the polar curve of a logarithmic spiral, which, however, tends to be nearly circular for deeper depths of embedment. The size of rupture surface increases with an increase in density of fill soil that mobilizes higher resistance, leading to enhanced anchor capacity. The critical embedment depth beyond which the anchor breakout factor does not change much is found to be approximately 7 times the anchor height for dense soil, whereas it is approximately 5 times the anchor height for loose soil. The anchor when placed below the critical depth, settlement, and heave on the fill surface tend to be marginal.

In this study, a testing device was developed to analyze the characteristics of grouting diffusion in faults. To include the interaction of multiple grouting applications, tests consisting of four applications of grout were performed using three sets of grouting pipes. During the grouting process, the real-time injection pressure, injection rate, soil pressure, and seepage pressure were monitored. It was found that the curves of both injection pressure versus time and injection rate versus time showed a wavelike relationship. Soil pressure and seepage pressure showed an obvious response to grouting; both increased continuously during grouting and decreased gradually when grouting was stopped. To expose the diffusion of the grout, 23 sections were cut through the medium, and 2,197 sets of the coordinates and thicknesses of exposed grouting veins were collected. It was found that the grouting veins formed by the first and fourth groutings, respectively, had larger sizes and larger spans. Based on the collected coordinates, the three-dimensional diffusion shape of the grout was sketched for the four grouting tests. Results show that the interactions of multiple groutings are mainly reflected in injection pressure and the distribution of the grouting veins. These conclusions can be used to further develop grouting theory.

Fracture-dominated flow in fractured rocks is of interest in many areas of scientific and technical research. In contrast to the continuum approach, this study employed a discrete fracture model method to analyze water movement in unsaturated fractured rocks, in which the flow behavior for single fractures is governed by Darcy’s law and the Richards equation, and the partial differential equations defined on the whole fracture network domain were formulated. A systematic finite-element algorithm was developed along with a corresponding numerical procedure. The results for the porous medium indicate that the proposed method is valid. Good agreement was found between the numerical predictions and experimental observations, and thus the equivalent discrete fracture network model may be used in place of the continuum model. The infiltration seepage analysis in a fractured rock slope demonstrated that the distribution of fracture-dominated flow was heterogeneous and that the movement of variably saturated seepage flow was substantially influenced by the orientation of fractures.

This study integrates microseismic data and data from hundreds of rockbursts of different intensities that occurred in a water drainage tunnel and four deep headrace tunnels at Jinping II Hydropower Station in Sichuan Province, China. The tunnels with overburden depths between 1,900 and 2,525 m, the maximum principal stress of which reaches 63 MPa in a rock mass, is composed mainly of marble. The tunnels have a total length of 12.4 km. The microseismic energy produced during the development of immediate rockbursts induced by the excavation by the drill-and-blast method (DBM) and a tunnel-boring machine (TBM) were studied. The results indicate that the daily maximum microseismic energy can be used as a basis for estimating rockburst intensity. The daily maximum microseismic energy (logarithm) corresponds to intense rockbursts (>6), moderate rockbursts (between 5 and 6), weak rockbursts (between 4 and 5), and no rockbursts (<4). Before the occurrence of intense rockbursts, there were numerous weak and moderate rockbursts during TBM excavation, whereas such a phenomenon was not observed during DBM excavation. The microseismic energy (logarithm) primarily concentrated in the range of 1 to 5 under TBM excavation, which is concentrated in the range of –1 to 4 under DBM excavation. For rockbursts of the same intensity, the range of microseismic energy remained the same for either type of excavation method. The distribution range of the microseismic energy moved in the direction of high energy as the level of rockburst intensity rose (intense rockbursts > moderate rockbursts > weak rockbursts > no rockburst). Microseismic energy can be used as a guideline for building a warning system and reduce the risk of rockbursts during construction.

The influence of gradation and particle shape on the small-strain Young’s modulus of dry sands is investigated through a comprehensive set of resonant column tests in the flexural mode of vibration. Experiments are performed on an array of sands with different coefficients of uniformity and particle shapes. The effect of gradation is investigated using tests on sands with similar particle shapes. The effect of particle shape is then examined through the experimental results on sands with a range of particle shapes. A new model is developed to incorporate the effects of gradation and particle shape into the prediction of the small-strain Young’s modulus. The proposed model is verified and compared with the existing models in the literature using the state parameter in the critical state soil mechanics framework. It is shown that the proposed model outperforms the previous ones considering the significant effect of particle shape on the small-strain Young’s modulus. Using the theory of elasticity, a model is developed for the prediction of Poisson’s ratio for sands taking into account the effects of particle shape and gradation.

The cavity-contraction method has been used for decades for the design of tunneling and prediction of ground settlement by modeling the cavity-unloading process from an in situ stress state. Analytical solutions of undrained cavity contraction in a unified state-parameter model for clay and sand (CASM) are developed in this paper to predict soil behavior around tunnels. The overall behavior of clay and sand under both drained and undrained loading conditions could be properly captured by CASM, and the large-strain and effective-stress analyses of cavity contraction provide the distributions of stress/strain within the elastic, plastic, and critical-state regions around a tunnel. The effects of ground condition and soil model parameters are investigated from the results of stress paths and cavity-contraction curves. Comparisons of the ground-reaction curve and the excess pore pressure are also provided between the predicted and measured behavior of tunneling by using data of centrifuge tunnel tests in clay.

This paper proposes an efficient hybrid approach for analysis of the responses of piled-raft foundations subjected to coupled loads (combination of vertical loads, horizontal loads, and moments) in layered soils. The proposed method comprehensively accounts for pile–pile, pile–soil surface, soil surface–pile, and soil surface–soil surface interactions. Moreover, to capture the influence of embedment and active/passive effects of piles, a modified Vesic’s subgrade modulus for embedded piles and passive piles was adopted. To avoid a large number of time-consuming integration processes, the shear displacement method and elastic foundation beam method were employed to calculate the vertical and horizontal responses of a single pile, respectively, and the results were then extended for the pile group. The results calculated with the proposed method for piled-raft foundations in layered soils were found to have good agreement with those obtained from the more rigorous finite-element methods (FEMs) and elastic theory method in layered soils. It was found that the proposed procedure can accurately predict the responses of piled-raft foundations under complex loads in layered soils.

Electroosmotic consolidation can be used as an efficient technique for soft soil improvement. Considering the limitation in previous theories that soil parameters keep constant during electroosmotic consolidation, the nonlinear relationships between soil compressibility, hydraulic and electroosmosis conductivities, and void ratio are incorporated in a one-dimensional model in the present study. The analytical solutions for the ultimate excess pore-water pressure and surface settlement are derived. A comparison between the proposed analytical solutions and traditional theory indicates that the nonlinear variation of hydraulic conductivity results in a larger ultimate excess pore-water pressure, whereas the nonlinear variation of electroosmosis conductivity leads to a smaller one. The effects are more significant for soils with higher compressibility. The nonlinear variation of soil compressibility exhibits remarkable impact on the development of excess pore-water pressure when the nonlinear variations of hydraulic and electroosmosis conductivities are considered. Compared with the ultimate excess pore-water pressure, the impact of nonlinear variations of soil parameters on the ultimate surface settlement is less significant.

The present paper investigates the propagation of SH waves in a finite thicker layer of the void pore sandwiched by heterogeneous orthotropic media. In the upper semi-infinite medium initial stress, density and shear moduli are assumed to vary hyperbolically, whereas in the lower semi-infinite medium linear variation in initial stress, density and shear moduli are considered. The study reveals that, under assumed conditions, there may be two types of SH waves. The first front depends on the void parameter and velocity of shear wave of the medium, whereas the second kind of SH wave is affected only by the void parameter. The study also shows that SH waves propagate in an elastic homogeneous layer between two heterogeneous semi-infinite media. To study the effect of void parameter as well as heterogeneity and initial stress parameters, the velocities of SH waves are calculated numerically and presented in a number of graphs.

The analysis of slope stability problems in engineering practice requires considerable attention for the three-dimensional (3D) effect of plan curvature of the slope. This paper quantifies this effect by a dimensionless parameter of the relative curvature radius of the slope (R/H) and proposes a set of 3D stability charts that can be used to estimate the factor of safety (FOS) of convex and concave slopes in plan view with homogeneous soil, extending those currently regularly used for 3D straight slope stability evaluations. To simplify the computational process, an alternative way to perform the FEM with the strength-reduction technique is used herein in the slope stability analysis. The strength-reduction analysis results in this paper together with results of other researchers were found to bracket the FOS to within ±5% or better and therefore can be used to benchmark the solutions of other methods. Changing the relative curvature radius of the slope (R/H) shows that concave slopes are more stable than straight slopes, but that convex slopes are less stable; moreover, the 3D effects are more significant in slopes with friction/cohesive soils with smaller values of R/H. Numerical 3D results are presented in the form of dimensionless graphs, which represent a convenient tool for practicing engineers to estimate the initial stability of excavated or artificial slopes.

A distinct feature of overconsolidated (OC) clays is that their dilatancy behavior is dependent on the degree of overconsolidation. Typically, a heavily OC clay shows volume expansion, whereas a lightly OC clay exhibits volume contraction when subjected to shear. Proper characterization of the stress-dilatancy behavior proves to be important for constitutive modeling of OC clays. This paper presents a dilatancy relation in conjunction with a bounding surface or subloading surface model to simulate the behavior of OC clays. At the same stress ratio, the proposed relation can reasonably capture the relatively more dilative response for clay with a higher overconsolidation ratio (OCR). It may recover to the dilatancy relation of a modified Cam-clay (MCC) model when the soil becomes normally consolidated (NC). A demonstrative example is shown by integrating the dilatancy relation into a bounding surface model. With only three extra parameters in addition to those in the MCC model, the new model and the proposed dilatancy relation provide good predictions on the behavior of OC clay compared with experimental data.