International Journal of Geomechanics

Across the globe, rapid urbanization demands the construction of tunnels within the vicinity of high-rise buildings supported on piled raft foundations. As a consequence, ground movements caused by such tunneling works could interfere with the serviceability of the foundations. Hence, the prediction of tunnel-induced ground deformation is of utmost importance. In the current study, a three-dimensional numerical analysis was carried out to study the response of an existing piled raft foundation with a 2 × 2 pile arrangement subjected to ground movements induced by a 6 m-diameter tunnel. The results obtained from the numerical simulations were further compared with a field study. The field measured lateral pile deflections were found to be in fair agreement with those computed using the present method. The numerical analysis was then extended to understand the influence of various factors, such as tunnel diameter, tunnel longitudinal axis, pile diameter, pile position from tunnel, and soil stiffness on the response of pile raft in the vicinity of an adjacent tunnel. The results obtained from the parametric study was finally summarized in simple semi-empirical equations to estimate the maximum lateral deflection and bending moment for both short and long piles.

Understanding the dynamic mechanical behavior of transversely isotropic rocks is essential in various fields of rock engineering, such as tunnel digging, blasting, and underground excavation. The bedding structure and strain rate determine the failure features of transversely isotropic rocks. Dynamic compression tests of transversely isotropic phyllites with different bedding angles were carried out using the split Hopkinson pressure bar (SHPB) approach to study the dynamic mechanical properties of transversely isotropic rocks. The resulting failure modes were characterized as two types (class I and class II) to describe the deformation behavior and fracture patterns under different strain rates. Both the strain rate and bedding angle influence the dynamic compressive strength. The dynamic compressive strength changes in a U-shaped trend as the bedding angle increases under similar strain rates. This trend becomes more pronounced as the strain rate increases. The failure patterns of the specimens tested under different strain rates are diverse. To gain a better understanding of the dynamic compressive behavior of phyllite, the discrete element method (DEM) was utilized to reveal the microfracture mechanism and failure process under extreme loads with the help of SHPB testing. The validity of the numerical simulation was verified by comparing the numerical results with the laboratory results. The thresholds dividing class I and class II failure for different bedding angles were investigated by applying different impact velocities. A scaling law was proposed to describe the increase in the dynamic strength of transversely isotropic phyllites. In addition, the microcrack propagation and microcrack type were analyzed to explore the influence of the bedding structures on the failure pattern and compressive strength. Different failure patterns form from different microcrack propagation processes, and the resistance of microcrack generation determines the strength of phyllites with different bedding angles.

Geocells are three-dimensional polymeric hexagonal pockets that provide lateral confinement to the soil, thereby increasing the bearing capacity of the soil bed. This paper briefly reviews past studies on geocell reinforcement of soil and presents a new product, cells made out of natural coir fiber, as an alternative to commercially available high-density polyethylene (HDPE) geocells. A series of model plate load tests were conducted on unreinforced soil and on soil reinforced with coir geocells to understand the soil reinforcement mechanism. It was observed that with the introduction of coir geocells, the load-bearing capacity of the soil bed increased up to three times and a significant reduction in the settlement was observed in the underlying weak soil bed. The study also presents a comparative performance evaluation of the natural coir cell-reinforced soil with conventional HDPE geocell-reinforced soil. Further, this paper analytically demonstrates the influence of the lateral resistance effect and vertical load dispersion effect incorporated by coir cells in strengthening the soil bed.

In this study, a novel effective stress cell based on fiber Bragg grating (FBG) sensing technology is developed for direct measurement of effective stress in saturated soil. The primary concept of direct measurement is that the pore-water pressures acting on both front and back surfaces of the sensing plate do not induce the deflection of the sensing plate, and thus the measured deflection of the sensing plate is caused by the effective stress only. The calibration results of the FBG-based effective stress cell (FBG-ESC) demonstrate a good linearity between the Bragg wavelength of the FBG sensor and the applied pressure. The workability and performance of the FBG-ESC in a saturated soil have been verified in a physical model test subjected to vertical pressures. It is found that the effective stress data directly measured by the FBG-ESC agree well with the effective stress values calculated, according to the effective stress principle, from the difference between the total stress and pore-water pressure measured by conventional transducers. All these results indicate that the novel FBG-ESC is capable of directly measuring the effective stress in a saturated soil.

In this study, a numerical model is developed to study concrete-filled FRP tube (CFFT) pile behavior and interactions with foundation soil under lateral loading. The model, based on nonlinear finite element analysis (NFEA) and the disturbed state concept (DSC), considers material and geometrical nonlinearity as well as the interface of soil with fiber-reinforced polymer (FRP). Furthermore, the structural and geotechnical performance of the interface of soil and CFFT pile is studied by utilizing 3D finite element models (FEMs) of full-scale field tests conducted during the construction of a highway bridge on Route 40 in Virginia. Based on deflection along the length of the pile, the model results are in good agreement with the experimental data. To investigate the effects of various parameters on the behavior of CFFT piles and local buckling, a parametric study was also performed on different geometrical and material properties, including the pile diameter to length ratio, FRP tube thickness, concrete strength, and soil properties. It was found that the surrounding soil and length to diameter ratio exerted the most noticeable influence, followed by concrete strength. The FRP thickness had the least impact on the results.

Shales are the most common materials on the Earth's surface that are frequently encountered in various energy, environmental, and engineering applications. Numerically predicting the mechanical behavior of shales is of great importance in the geomechanics community. A coupled plasticity and damage constitutive model is developed in this study to describe the mechanical behavior of shales that spans the prepeak, peak, and postpeak regions. A concept of a damaged part of geomaterials, which possesses residual shear strength, is introduced in the proposed model. A thermodynamic conjugate force is presented by accounting for the residual shear strength of the damaged part. Procedures to determine the model input parameters and an algorithm to implement the constitutive model in a numerical code are presented. Validation against experimentally observed stress–strain curves of shales shows that the proposed model can predict the mechanical behavior of shales under various stress paths and confining stresses from the pre- to postfailure regimes.

The evolution of fabric under loading plays an important role in the micromechanical analysis of granular materials. This paper addressed this issue from the perspective of the discrete element method (DEM) simulation. A series of drained tests were performed under true triaxial stress conditions. Isotropic assemblies with different densities were sheared to the critical state under three kinds of loading paths. The evolution of three-dimensional fabric under general stress conditions was investigated by analyzing the influences of density, shear mode, and loading path on the fabric anisotropy. Numerical results revealed some evolution patterns of fabric with strain and stress. The evolutions of fabric components and deviatoric fabric were dependent on shear mode. An ultimate fabric anisotropic state was achieved at a relatively large strain for a given shear mode, which agreed with the theoretical expectation of anisotropic critical state theory. Noncoaxialities between fabric, stress, and strain tensors were also observed in simulations and these noncoaxialities needed to be rationally incorporated into fabric evolution laws.

This paper presents an analytical solution for one-dimensional nonlinear consolidation of a saturated clay layer with variable compressibility and permeability under various cyclic loadings. Based on the assumption that the initial effective stress was constant with depth and the nonlinear variations of compressibility and permeability were expressed by the logarithm relations (e − log σ′ and e − log k_v), two new variables were introduced to the 1D nonlinear consolidation equation. The analytical solutions were derived for trapezoidal, rectangular, and triangular cyclic loadings. The presented solution could degenerate into all of the existing solutions for nonlinear consolidation, which showed the analytical solution proposed in this paper was the most general one for nonlinear consolidation. The validity of the proposed solutions was verified against the numerical results from the finite difference method (FDM). The effects of different parameters on nonlinear consolidation behavior of the saturated clay layer subjected to various cyclic loadings were investigated using the solutions developed. The proposed solutions could be effectively utilized in the analysis of nonlinear consolidation of a saturated clay layer under various cyclic loadings.

A new procedure is presented in this paper to assess the tunnel face stability in anisotropic and nonhomogeneous soils. The three-dimensional (3D) rotational failure mechanism proposed by Subrin and Wong ( 2002) is used to include the anisotropic and nonhomogeneous soil parameters into the computational model. Regarding previous findings, the cohesion of soils is modeled as varying with direction to account for the anisotropy and linearly increasing with depth for the nonhomogeneity. A more complex case with two-layer soils is considered where sudden changes of cohesion, nonhomogeneous coefficient, and unit weight at the interface are assumed. A degraded program and a numerical simulation with FLAC^3D are performed to validate the proposed methodology. The critical support pressures are calculated using the proposed approach to show the influences of the involved parameters on tunnel face stability. Sixteen combinations of different parameters are specially chosen to investigate their influences on the shape of the failure block. According to the numerical results, the 3D profiles of failure mechanisms are plotted to give a visual description of face failure.

A hidden karst cave has a prominent influence on the design and construction of underground engineering. In order to improve the automatic identification accuracy of hidden karst cave areas and the acquisition accuracy of characteristic parameters in borehole radar signals, combined with the reflection characteristic relationship between radar electromagnetic waves and hidden karst caves, research methods on borehole radar image pre-processing and feature parameter extraction of hidden karst caves are carried out. First, based on the original signal of a borehole radar, the reflection characteristic relationship between the electromagnetic waves of the borehole radar and a hidden karst cave is established, and the geometric model of borehole radar detection of hidden karst caves is formed. Then, the reconstruction of borehole radar signals is realized by searching the peak position of Pmusic function combined with the subspace MUSIC method. Combining the continuity of hyperbola and the gray level difference of a nonreflective region, an improved variance method is proposed, which is more suitable for the actual borehole radar image segmentation. It realizes the suspected hidden karst cave inversion by setting a threshold of continuous pixels, a simultaneous gradient operator, and a maximum interspecific variance method. Finally, according to the geometric model of borehole radar detection, the energy-weighted fitting of a hyperbolic profile is carried out, and the improved Hough transform method is used to solve the multiple characteristic parameters of the hyperbolic model, so as to extract the characteristic parameters of the hidden cave from the borehole radar signal. The example analyzed proves that the method is feasible and accurate, which can provide important data support for underground engineering.

Two of the mesh-based numerical approaches suitable for geotechnical large deformation problems, the multimaterial arbitrary Lagrangian–Eulerian (MMALE) and the coupled Eulerian–Lagrangian (CEL) methods are investigated. The remeshing step in MMALE was claimed to hold advantages over CEL, but its effects on application problems are not studied in detail. Hence, the possible capabilities and improvements of this step are studied in three large deformation geotechnical problems with soil–structure interaction. The problems are validated and verified using experimental and analytical solutions, respectively. By using the remeshing step in MMALE, a smoother material interface, lower remap related errors, and better computation costs are achieved.

A slip-failure surface forms in the backfill soil upon sufficient yielding or movement of the wall that retains the backfill soil. The shape of the slip-failure surface plays an important role in estimating the lateral earth pressure, including its magnitude and location of its resultant force. As retaining walls at times must be built with narrow and constrained backfill space, this study presents an analytic derivation of the slip-surface shape in narrow cohesionless soil behind a rigid retaining wall under translation movement mode of the wall. Results of a series of experimental tests were presented to demonstrate the effects of narrow backfill spaces on forming the slip surface and that the slip surfaces are curvilinear planes developed from the heel of the retaining wall to the crest of the backfill. Based on the experimental findings, a rigorous analytic derivation using a variational limit equilibrium method is conducted to determine the governing equation for the shape of the slip surface in the narrow backfill soil. The analysis reveals that the active failure plane of the narrow soil behind a rigid retaining wall agrees well with a logarithmic spiral plane. The derived log-spiral slip-surface plane is further verified by experimentally observed slip surface and measured active lateral earth pressure. Substantial discrepancy was observed in the lateral earth pressure distribution between the logarithmic spiral slip surface and the assumed linear planar slip surface, indicating that the assumption of a linear planar slip surface in narrow backfill may result in significantly erroneous estimation and lead to an overly conservative and uneconomical design. Furthermore, a threshold value of 0.5 is identified for the backfill width/height ratio that distinguishes the narrow backfill from a sufficiently wide backfill.

A fractured rock mass was characterized by strong heterogeneity, discontinuity, and anisotropy. The study of flow in a fractured rock mass was a complex and challenging task. As the main seepage channels of a fractured rock mass, the fracture network was mainly affected by the fracture density, trace length, aperture, and direction angle. In this paper, the influence of fracture parameters on the permeability of the fracture network was studied by orthogonal experimental design and numerical modeling. A series of fracture networks were established to obtain seepage rules and permeability. The results showed that the increase in fracture density, trace length, and aperture increased the permeability of the model and that the fracture direction angle affected the pressure gradient and the anisotropy of the seepage in the model. The sensitivity of effective parameters on the discrete fracture network permeability performance was obtained. The influence factors of K₁ were density, trace length, aperture, and direction angle in that order. The influence factors of K₂ were direction angle, density, aperture, and trace length, in that order. The influence factors of K₁/K₂ were direction angle and density, aperture, and trace length in that order. These results could be used for parameter adjustment of fracture network modeling and determining the complex seepage characteristics in naturally fractured reservoirs.

Pattern design and management of blasting in open pit mining have been constantly of great interest to many mining engineers so as to reach an appropriate degree of fragmentation for loading, hauling, and crushing systems. Inappropriate fragmentation incurs extra costs in the form of secondary blasting, disruptions in the loading and hauling process, and so forth. To tackle this problem, it is necessary to predict the blast-induced fragmentation. Numerous methods have been proposed by many researchers to predict fragmentation. Regarding technological advancements, and with the advent of numerical codes, the restrictions of empirical methods for the prediction of blast-induced fragmentation can be overcome. The present study developed a model for the estimation of blast-induced fragmentation using a discrete-element method coupled with image processing techniques. In the numerical model, Voronoi elements were used to simulate microcracks of rock materials. Preexisting joints were also present in the model; prior to the blasting, their information was elicited in the area of interest (the Hegmatan limestone mine, Iran). After the blasting, the real fragmentation and modeled fragmentation were compared using image processing software. The results obtained from the numerical modeling were in good agreement with the real data, validating the simulation procedure. Hence, the Voronoi discrete-element method coupled with the image processing technique is appropriately capable of modeling the blasting-induced fragmentation in a discontinuum. Finally, the influence of different parameters, namely delay, presplitting, preexisting joints, discontinuity spacing, and spacing-to-burden ratio, on fragmentation indices were numerically simulated and investigated. The results showed that the lack of delay increases D₅₀ of fragments from 32.57 to 95.94 cm, the application of presplitting negligibly affects fragmentation, and the preexisting joints in the study area enhanced the fragmentation performance.

Saw-cut rock surfaces, classically utilized to estimate basic friction angle of discontinuities by means of tilt test and other procedures, may seem planar to the naked eye. Nevertheless, they actually present roughness at a micrometric scale. Aiming at characterizing some of these saw-cut rock surfaces and assessing the possible implications between their microscale topography and the resulting tribological behavior, the authors of this study resorted to the 3D focus-variation technique to analyze different surface-texture parameters. Tilt tests were carried out on specimens cut on three rock types, and the involved sliding surfaces were evaluated at a microscale for different testing stages (prior to any test and after two series of repeated tests). An apparently logical inverse correlation between repeated testing and friction angle has been observed, more marked for the smoother surfaces. Higher roughness at the scale of the analysis tends to produce lower friction-angle values, as otherwise observed for mismatched natural rock surfaces. In addition, saw-cut rock surfaces present systematically negative skewness and high values of kurtosis for their height distributions, indicating the occurrence of narrow and deep pits or valleys. Directional hybrid parameters and, in particular, the root mean square (RMS) of the gradient of the surface in the direction of sliding correlates rather well with the measured sliding angle. The authors concluded that the 3D focus-variation technique represents a powerful tool to assess surface-texture parameters of saw-cut rock surfaces, in addition to being useful for understanding some features of the tribological, or wear and frictional, behavior of these type of surfaces.

Freeze–thaw weathering of rock masses in cold regions is mainly caused by the freezing deformation of rock exposed to subfreezing temperature. The deformation behavior of freezing rock is focused on in this research. The phase transition process of the water–ice system in freezing rock is analyzed. A time-dependent variable named freezing degree is applied to describe the percentage of water phase changed into ice in the rock. The mechanical character of the freezing rock is investigated based on compression tests of freezing sandstone. Accordingly, the strength and yield criteria for freezing rock are analyzed. Next, a quasi-elastic-plastic-creep model is proposed to describe the time-dependent behavior of freezing rock. The total strain of freezing rock is decomposed into three parts, including the thermal strain of the rock matrix, the strain caused by the confining pressure, and the freezing strain caused by the phase transition of water in the rock. The freezing degree function is applied in the constitutive model, which is further redeveloped using the programming language VC++. Finally, a tunnel in a cold region is simulated using the new constitutive model. The result indicates that the new model can simulate the time-dependent behavior of freezing rock.

An improved genetic algorithm is proposed to optimize the potential sliding surface of slopes. Compared with a conventional genetic algorithm, the genetic recombination between the previous generation and the newly generated population around the local optimal individual of the previous generation is performed in the improved genetic algorithm, while the genetic recombination between the previous generations is performed in the conventional genetic algorithm. The improved genetic algorithm has the advantage of faster convergence than the conventional genetic algorithm. Moreover, the rigorous limit equilibrium method is applied to define the safety factor of slopes. Two examples are illustrated to prove the efficiency of the improved genetic algorithm.

This paper proposes a new arrangement of geotextile reinforcement stiffness for large geotextile mat cofferdams that often suffer from the failure of the bottom layer mat. Cofferdams using this new reinforcement method are poorly understood and require a thorough study to explore their behavior lying on soft sediments which is the prevailing situation for land reclamation projects. This paper investigates the performance of large geotextile mat cofferdams with this new type of reinforcement using a systematic numerical study. The numerical finite element models (FEM) were validated against experimental observations and field test data, where the soil flow mechanism and the cofferdam deformation were investigated. Through discussion of the failure mechanism, limiting stack height, and geotextile tension distribution in a systematic parametric study, it was concluded that the effects of the geotextile stiffness of the base mat of the cofferdam, the strength of soft clay, and the width of cofferdam base were significant, and the negligible parameters include the strength of sand fill and cofferdam slope. Based on the results, it was found that large geotextile mat cofferdams with this new type of reinforcement demonstrate two types of failure mechanisms: so-called local and global failures. An equation is proposed to identify these two different failure mechanisms, which consider the properties of the sand fill, the underlying soft sediment, and the geotextile material. A general guideline is proposed to help design large geotextile mat cofferdams with this new reinforcement, using which both the limiting stack height and the safety factor of cofferdam can be evaluated.

This paper presents an elastoplastic two-surface model for the description of the stress–strain behavior of unsaturated cohesive soils under suction-controlled cyclic loading conditions. First, the model was developed within the framework of plastic incremental flow theory combining Barcelona Basic Model (BBM) with two-surface model. Second, by extending the Masing's rule to a general multiaxial case, the point at which the stress path reverses is taken as the memory center. Third, a bounding surface and a geometrically similar loading surface evolved in stress space through the plastic hardening criterion suggested by the corresponding author. The characteristics of nonlinear, cyclic plasticity, and deformation accumulation of unsaturated cohesive soils under cyclic loading can be described by the evolution of the constant-suction cross-sections of the bounding and loading surface in the stress space. Model simulations of the stress–strain response taking into consideration the effect of suction, net cell confining pressure and dynamic stress amplitude are compared with the results obtained from a number of suction-controlled laboratory monotonic and cyclic triaxial shear tests. In addition, typical predictions are described and compared with characteristic trends of the behavior of unsaturated soils. The comparisons indicate that the elastoplastic two-surface model can simulate the mechanical behavior of unsaturated soil under cyclic loading.

In this paper, the performance of a laterally loaded single pile located in a mountainside was predicted by a modified strain wedge (SW) technique and, in particular, the emphasis is on quantifying pile–soil interactions based on static equilibriums. The effects of surrounding soils on the pile shaft were idealized by using two different wedge models, depending on the relative location between the pile and soil. The proposed method is simultaneously validated by numerical solutions and laboratory observations and, therefore, sensitivity studies on the location of the pile were further investigated, especially for the summit of the mountain.

A hybrid element method is presented for the dynamic analysis of piles and pile groups embedded in exponentially graded transversely isotropic media. In this method, the piles are modeled using finite elements, while the dynamic pile–soil–pile interaction is modeled through superposing the response of a series of massless rigid radiation discs defined at the nodal points of the elements. A set of complete potential functions are used to derive the analytical solutions for the lateral vibration of radiation discs embedded at different depths in a nonhomogeneous transversely isotropic half-space. A Boussinesq-type loading distribution is introduced to act on the radiation discs to satisfy the displacement compatibility conditions between piles and soil. Numerical results and comparisons with known analytical/numerical solutions are presented to demonstrate the application of this method. The influence of the soil nonhomogeneity on the lateral compliances of piles and pile groups is particularly emphasized.

The objective of this study is to estimate dynamic compaction (DC) induced settlement of municipal solid waste (MSW) landfills using numerical modeling. Finite element (FE) based analysis is carried out and the corresponding reduction in waste volume, crater depth, and settlements induced at the ground surface due to densification are examined for a range of compression ratios of MSW. The response of MSW is modeled by adopting the Drucker-Prager constitutive law, and the effect of large strains developed during DC is simulated using the arbitrary Lagrangian-Eulerian (ALE) remeshing approach. The developed model is validated by comparing the numerical results with published settlement values from various landfill sites. The effectiveness of DC in increasing the design life and overall capacity of MSW landfills is subsequently investigated by varying waste compressibility, energy, momentum, and tamper radius. The analysis results indicated that the optimum number of tamper drops on MSW vary in the range 5–12 depending on waste compressibility, whereas, the optimum radius to be adopted in the field is approximately 1.6 m. In addition, the crater depth was found to increase for wastes with higher compressibility, and the effect of tamper momentum was found to be pronounced compared with tamper energy. Based on the optimized design parameters obtained, an empirical equation is formulated for predicting DC induced settlement of MSW landfills in the field. The utility of this study is to aid in decision making regarding the implementation of DC to MSW landfills and to focus the efforts of full-scale expensive field trials.

It is an ongoing problem to develop a solution to predict ground deformation induced by shallow tunnels construction in dry soils. This study proposes a closed-form elastic analytical solution and a plastic analytical solution for calculating the longitudinal settlement trough. Meanwhile, a semi-analytical solution is further developed for better fitting tunneling-induced ground deformation, where the metaheuristics optimization algorithm particle swarm optimization (PSO) is employed to identify the empirical parameters of the proposed semi-analytical solution. A uniform formulation with the combination of analytical and semi-analytical solutions accounting for tunnel uniform convergence and ovalization deformation modes is proposed. A 3-dimensional numerical model and centrifuge test results are used to validate the prediction capability of the proposed solutions in predicting longitudinal and transverse settlement troughs, respectively. The results indicate the proposed semi-analytical solution can overcome the deficiency of analytical solutions, and the predicted results show great agreement with actual tunneling-induced transverse and longitudinal settlement troughs. A simple linear relationship is discovered between coefficients of the proposed semi-analytical solution identified by PSO and their influential factors that assign physical meaning to these empirical coefficients and also provides a straightforward method to estimate coefficients effectively.

An overlying sand layer combined with a concrete arch operates as a buffering structure for dealing with rockfall disasters in tunnel construction, especially through karst and weak strata. However, the buffering effect and construction parameters of overlying sand technology always depend on experience. To successfully deal with rockfall disasters encountered when a tunnel passes through a top karst cave or collapse cavity, it is essential to study the buffering effect of overlying sand technology, to give a quantitative estimation of the rockfall impact force, and to optimize the construction parameter. First, a sand layer overlying a concrete arch supporting scheme in tunnel is introduced. For the optimization of the sand layer construction parameters, a series of discrete element-based simulations are employed to analyze the influence of the sand layer thickness, friction coefficient between sand particles, and sand layer porosity on the buffering performance. The results indicate that the thickness of the overlying sand layer is the dominant factor affecting the buffering effect of supporting structure. Thus, overlying sand thickness is selected as the key factor to be optimized. A collapse cavity in the Yuelongmen tunnel, Chengdu–Lanzhou Railway Project is then taken as a case of parameter optimization. Finally, construction parameters of overlying sand layer technology applied in other tunnels are discussed, which further validates the numerical simulation process and parameter optimization. This study verifies that overlying sand layer technology is an effective preventative treatment for limiting the impact of rockfall in tunnels with overhead cavities. Moreover, the results provide a fundamental reference and guidance for dealing with rockfall disasters in tunnel construction.

This paper investigates fracture toughness and subcritical crack growth of marble, lherzolite, and amphibolite under different environments aiming to better understand the effect of environment, especially the acidic solution, on the fracturing behavior of the three rocks. Specifically, a series of load relaxation (RLX) and rapid loading tests were performed on double-torsion (DT) specimens to understand the subcritical crack growth velocity V versus the stress intensity factor K_I relation and evaluate the fracture toughness K_IC for the three studied rocks in air, distilled water, and acidic solutions with pH of 6.0 and 3.0, respectively. The results indicate that, for all three studied rocks, the percentage of load drop during RLX increases and the fracture toughness decreases when the environmental condition changes from air to distilled water and to an acidic solution with higher acidity. The measured log K_I−log V relation follows the Charles theory well, and the crack velocity and the final crack growth length both increase and the subcritical crack growth index n decreases when the environmental condition changes from air to distilled water and to an acidic solution with higher acidity. The results also show that the weakening effect of an acidic solution on the marble is much greater than that on the lherzolite and amphibolite.

Three-dimensional finite-element analyses of the inclined pullout behavior of geogrids embedded in three types of anchors (run-out, I-type, and L-type) are presented in this paper. The soil behavior is represented by the elastic–perfectly plastic Mohr–Coulomb (MC) model and the geogrid behavior with linear-elastic plate elements. The geogrid is modeled using the geometrical and index properties of the geogrid used in model tests. The predicted results from the finite-element analyses are compared with the corresponding model test results. The peak pullout force values for different values of inclinations and types of anchors are predicted with reasonable accuracy by the present numerical model. However, the results show that the post-peak response for run-out and I-type anchors and the stiffness in the case of I-type and L-type anchors are not satisfactorily modeled.

The discrete element method–finite difference method (DEM--FDM) numerical simulation was conducted to investigate the failure process and the bearing mechanism of the single stone column in soft soil beneath rigid loading. The stone column was modeled by discrete rigid blocks, and the surrounding soil was represented using the Mohr–Coulomb constitutive model. The settlement, bulging deformation, and failure process were tracked during the complete loading process, which enables the footing–column–soil interactions to be observed visually. The typical load–settlement curves and corresponding failure mechanisms are graphically illustrated according to the numerical analysis. The larger loading plate will help to enhance the bearing capacity of stone columns but not intensively. The stiffness of surrounding soils controls the final failure mode. The local shear failure mode is much more likely to happen for the single stone column beneath rigid loading when the surrounding soils are relatively soft compared to their shear strengths. The existing analytical formulas may overestimate the ultimate bearing capacity of a single stone column in soft soils.

Pressure plate extractor tests were performed on a residual clay soil over three drying–wetting cycles. An adjustment of a soil internal structure, caused by the change in the stress and suction path, affects the soil–water characteristic curve (SWCC). The hysteretic loop size of the suction–void ratio, as well as the deformation, is influenced by the stress and drying–wetting cycles. Lower vertical stress together with fewer drying–wetting cycles implies an increased hysteretic loop size and deformation. On the basis of experimental data, the van Genuchten model was improved to evaluate the SWCC's void ratio dependency of deformable residual clay soils. When compared with the equation proposed in the literature, SWCC's dependency on the void ratio can be well quantified based on the form of the void ratio with variable stresses and suction. This model is validated using the experimental data that are applicable to several soils subjected to various hydromechanical paths, and the experimental results are proved to match well with the model prediction. According to the second-order polynomial function relationship between each parameter and the cycle number, the SWCC obtained after five drying–wetting cycles was recommended for long-term stability analyses of unsaturated residual soils.

An analytical procedure is presented for assessing the long-term load-carrying behavior of bored piles in clay, where the plastic volumetric strain of surrounding clay caused by creep is estimated by an advanced elasto-viscoplastic constitutive model. Two key soil parameters, the undrained shear strength and the shear modulus, which govern the load-carrying behavior of bored piles in clay, are determined from the definition of the quasi-overconsolidation ratio and the concept of the critical state theory-based Cam-clay model. The long-term load-carrying capacity of bored piles is evaluated based on the total stress method. Hyperbolic load-transfer models are developed with proper incorporation of the two developed soil parameters to predict the long-term load–settlement behaviors of the bored pile. The proposed framework is validated by predicting a pile field test on an existing bored pile (about 30 years) in clay, which was recently performed by the authors in Pudong New Area, Shanghai, and field static load tests on two single bored piles conducted by other researchers. Comprehensive parametric studies are conducted to explore the effects of secondary compression index and in situ soil properties on long-term load-carrying behavior of bored piles. The proposed procedure is expected to provide useful guidance for estimating the load-carrying behavior of existing bored piles in clay and take the ultimate aim of reusing them in practice.

Large deformation finite element analyses have been performed to simulate the installation of offshore skirted foundations in clay with different strength heterogeneity. The influences of loading rate and remolding during installation have been incorporated on the undrained shear strength of the soil. The mobilized frictional resistance at the skirt–soil interface has been linked to the sensitivity of the soil. Following installation, the short-term compression and uplift capacities of these foundations are estimated at different levels of embedment. After validating the numerical methodology by comparing results with available theoretical and experimental studies, detailed parametric research has been carried out for all practical ranges of parameters. Closed-form expressions are presented for estimating installation resistance and short-term ultimate compression and uplift capacities of shallow skirted foundations. The proposed equations predict the undrained ultimate capacities with a maximum error limited to 5% and can be directly used by practicing engineers.

Cross-flaws are very common in natural rocks. To date, the understanding of the failure process of rocks with cross-flaws is very limited. In this research, we study the influence of the cross-flaws geometry on the rock strength and coalescence modes with rock-like specimens. In this work, three groups of specimens with pre-existing cross-flaws are investigated: two aligned cross-flaws, two step cross-flaws, and two collinear primary flaws. The crack propagation and strength of specimens containing two parallel flaws are also studied to compare the results with those of specimens with cross-flaws. The results demonstrate that the cross-flaw geometry influences the rock bridge coalescence patterns in rock-like specimens. Specimens with two aligned cross-flaws and two step cross-flaws coalesce with tensile cracks in the rock bridge areas, while specimens with two collinear primary flaws coalesce with shear cracks. Specimens containing two cross-flaws may have a higher uniaxial compressive strength than specimens containing two parallel flaws, and the number of specimens with a higher uniaxial compressive strength is influenced by the cross-flaws geometry in the different groups. The cross-flaws geometry influences the strength of the specimens. In this research, specimens in the group containing two aligned cross-flaws have the highest mean uniaxial compressive strength, and specimens in the group with two step cross-flaws have the lowest strength.

Hydraulic fracturing is extensively applied as an effective stimulation technology to enhance coalbed methane recovery. Coal strength and permeability play critical roles in the performance of hydraulic fracturing, and acoustic emission (AE) provides useful information to evaluate this. Coal strength, permeability, and AE are all governed by coal rank and stress condition. However, the influence of coal rank and stress condition remains unclear. In this work, the coal strength, permeability, and AE are investigated under different confining pressures for different coal ranks in the laboratory. The results show these properties are mainly controlled by coal structure, particularly the development of pores and cracks. The compressive strength of coal presents a U-shaped trend with the vitrinite reflectance. However, as the confining pressure increases, the compressive strength raises, but its increase rate declines. In the process of loading stress, the permeability, and AE activities can be divided into three phases: compaction and elastic deformation phase, nonelastic deformation phase, and macroscopic failure phase. The initial permeability of low and medium-rank coals is higher than those of high-rank coals. In addition, as the confining pressure increases, AE activities and permeability weaken. The occurrence of abundant AE activities do not always suggest the generation of new cracks, but it can be regarded as an indicator, where the coalbed reservoir exhibits high permeability. Finally, based on these results, a new damaged model and a constitutive relationship between AE counts and stress are proposed to describe the coal-damaged evolution and predict its stress–strain behavior.

The response of existing tunnels to adjacent excavation at an oblique intersection angle is still unclear. This study investigated the deformation of an existing tunnel when new excavation was conducted obliquely, based on a case history from Tianjin, China. In this project, a cutoff wall was installed to protect the tunnel from excessive horizontal movement. Finite element analyses were then performed to investigate the optimization of the cutoff wall design. The monitoring results show that due to the oblique intersection, the tunnel rings near the narrow and wide boundaries of the excavation ultimately exhibited heave and subsidence after excavation. The tunnel also underwent significant torsional deformation and horizontal displacement toward the excavation. The maximum horizontal displacement occurred at the tunnel ring closest to the midpoint of the wide boundary of the excavation. The numerical analyses show that as the intersection angle between the cutoff wall and the excavation increased, the efficiency of the cutoff wall first decreased and then increased. The effectiveness of the cutoff wall parallel to the tunnel was up to 122% greater than that of the wall parallel to the excavation, justifying the installation of cutoff walls parallel to tunnels.

In this study, the finite difference method (FDM) coupled with a discrete fracture network (DFN) was utilized to analyze longwall top coal caving (LTCC) behaviors. The integrated FDM–DFN model enabled the influence of the preexisting fracture, stress redistribution, stress rotation, caving material compaction, and periodic rupture of roof strata to be superimposed on the failure process of top coal. It was revealed the LTCC influenced both magnitude and orientation of the principal stress within top coal. The minor and major principal stresses experienced successive peak points as top coal approached the LTCC face, and the corresponding principal axes rotated toward horizontal and vertical directions, respectively. The concentration of the major principal stress and the release of the minor principal stress resulted in the shear failure of top coal ahead of the LTCC face. The failure mode transferred from shear to tension at the rear of the face line. The principal stress rotation led to continuous variation in internal cohesion of top coal and brittle fracturing of the main roof resulted in dynamic load at the LTCC face. The stress rotation and roof rupture greatly promoted the failure process of top coal. This type of promotion was also provided by the preexisting fractures and adjacent goaf.

Stone columns (SCs) and sand compaction piles (SCPs) are widely utilized as effective methods to increase the bearing capacity and reduce the settlement of soft ground. In this study, a physical model test was conducted to compare the performances of the SC- and SCP-improved Hong Kong Marine Clay (HKMC) grounds. Finite-element (FE) modeling was performed to analyze the settlement and stress increment. A practical equation related to the area replacement ratio and the friction angle of columns is proposed for determining the creep improvement ratio of soft ground treated by columns, which agrees well with the creep improvement ratios from the FE simulations.

It is important to control the permeability of a mixture of foam and solid in many fields such as civil engineering, petroleum engineering, and material processing. An analytical model to estimate the coefficient of permeability of a foam-conditioned soil was developed in this study, based on the permeation theory of pure foam. In the model, water flow in the permeation channel enclosed by foam bubbles was derived using the Kozeny-Carman equation, where the reduction in the number of effective permeation channels due to the contact angle between foam bubbles and soil particles was considered. To validate the analytical model, a series of large-scale permeability tests were carried out on 18 foam-conditioned soils with various gradations and conditioning parameters, and the results were compared with the calculated coefficients of permeability. Although the calculated values underestimated the experimental values for some cases, they were in general good agreement. The validated analytical model indicated that, for fully conditioned soils, the permeability increased with an increase in the porosity of the conditioned soil and the effective particle sizes of the foam and soil.