International Journal of Geomechanics

Karst caves are often encountered during karst tunnel excavation, and the shape of the karst cave has an impact on the stability of the tunnel surrounding rock. This paper focused on the effects of karst cave shape on the stability and minimum safety thickness of tunnel surrounding rock. First, the 3D water-filled karst cave and tunnel models were established, and the tunnel excavation simulation under the different height–span ratios of the karst cave was carried out. Second, the stress and displacement fields of the surrounding rock were analyzed, and the change laws of stress and displacement with tunnel excavation were revealed. Third, on the basis of simulation results, the formulas for the minimum safety thickness of surrounding rock resisting water inrush were derived based on the catastrophe theory and strength theory. Finally, the numerical simulation and theoretical formulas were verified by contrastive analysis of the specific engineering project. The results showed that (1) as the height–span ratio of the top karst cave increases, the principal stress of the surrounding rock increases gradually, as well as the Y-displacement of tunnel vault and bottom; (2) the influence of height–span ratios of the top karst cave on the maximum principal stress and displacement of the tunnel vault is the largest; and (3) the formula for the minimum safety thickness of rock resisting water inrush is obtained based on the catastrophe theory. The research results have certain reference significance and engineering application value for the prevention and control of water inrush disasters in karst tunnels and other similar underground engineering construction.

Having a grasp of the variation in the fracture contact area is a kernel in the understanding of the permeability evolution of fractured rocks. However, the number of studies that focus on measuring the long-term variation in the fracture contact area under different conditions is insufficient. In this study, a series of short- and long-term permeability tests under coupled conditions is performed to check the performance of permeability. The results reveal that the permeability measured in the short-term tests shows reversible behavior and a dependence on the applied confining pressures and temperature. In contrast, the permeability in the long-term tests displays irreversible behavior and an irregular change under the constant confining pressure. In order to verify the evolution of permeability, microfocus X-ray computed tomography (CT) is developed to observe the changes in the internal fracture structure under the same conditions as those in long-term permeability tests by assembling a triaxial cell with heating capability. The fracture aperture and the fracture contact-area ratio are calculated by a CT image analysis technique. The image analysis results show that the estimated aperture is seen to decrease with an increase in the confining pressure and to also decrease with time under a constant confining pressure. Moreover, the increase in the fracture contact area under the constant confining pressure observed by X-ray CT is confirmed. This also corresponds to a decrease in permeability in long-term tests. The hydraulic aperture calculated from the permeability tests and that evaluated from the CT observation have a similar decreasing trend. Therefore, the CT observation can better capture the evolution of the internal fracture contact area. These experiments underscore the importance of mechanical compaction and/or mineral dissolution at contacts in determining the rates and the magnitude of permeability evolution within rock fractures.

In this paper, a semianalytical approach is presented to formulate an excavated cavity in Mohr–Coulomb soils subject to biaxial initial stresses. The response of cavity expansion within the plastic region was investigated by combining the Mohr–Coulomb criterion with the equilibrium equation. The elastic–plastic (EP) boundary was expressed by a new conformal mapping function with three unknown parameters, which were determined by the stress continuity condition at the EP boundary and the volume-conservation condition. In the elastic zone, the stress function was expanded into Fourier series for convenience of application and the coefficients of Fourier series were determined according to stresses at the EP boundary. An unassociated flow rule with a dilation angle of 0° was adopted in the plastic zone, and Hooke’s law governed the behavior of soil within the elastic zone. Comparisons between the proposed solution and Galin’s solution showed good agreements, which validates the proposed framework. Extensive parametric studies were also performed to explore the effects of the internal friction angle, cohesion, and coefficient of earth pressure at rest on responses of cavity expansion. The results suggested that an increase of the internal friction angle, cohesion, Young’s modulus of soil, and coefficient of earth pressure at rest all leads to a higher expansion pressure at the cavity wall, while the extent of the plastic region around the cavity shrinks with an increase of the aforementioned three parameters.

Joints with different angles in rocks have significant impacts on their fracture mechanisms. In this study, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and microcomputed tomography (Micro-CT) were used to study the microstructure characterization of sandstone, and digital image processing (DIP) technology has been applied for the characterization of sandstone mesostructures. DIP technology has been combined with RFPA2D to numerically investigate the mesoscale fracture behaviors of jointed sandstone with different dip angles. On the basis of the box dimension theory and digital image storage principle, Matlab was applied to develop a mesoscale fracture box dimension algorithm based on digital imaging, and therefore, an analysis method was established for the evaluation of mesoscale fracture damage degree based on fractal dimensions. Previous studies have revealed that the elastic modulus and compressive strength of the sandstone had significant anisotropy, and the compressive strength of sandstone had an approximately power exponential relationship with fractal dimensions; therefore, fractal dimensions could be applied to describe sandstone compressive strength. There were found to be five final failure modes in joint specimens with various inclination angles. Failure mode and damage degree could be determined by fractal dimensions and mesoscale fracture damage degree, respectively. As the fractal dimension became greater, failure mode became more complicated and mesoscale fracture damage was enhanced, resulting in more serious damage. This study is helpful in understanding the mechanical properties of sandstone in complex structural areas and provides a novel method for studying the evolution law of mesoscale failure in rocks.

Particle fracture significantly influences the constitutive behavior of sands and impacts many geotechnical engineering applications, such as hydraulic fracturing, pile driving, blast loading, and stability of dams. When a confined specimen of sand is loaded in 1D compression, particles ultimately fracture, causing permanent microscale deformations that contribute to the yielding behavior of the sand. The most common constituent of sand particles is silica mineral (quartz), which is well known for its natural abundance and high compressive strength. Such excellent properties make silica sand particles an excellent proppant for high-pressure hydraulic fracturing in the oil and gas industry and many other applications. This paper investigates the fracture characteristics of silica sand particles using 3D finite-element (FE) simulations of single particle crushing and confined 1D compression experiments. The 3D FE simulations were generated using digital image processing of in-situ synchrotron microcomputed tomography (SMT) scans, unique 3D meshing algorithms, and coding development in ABAQUS FE software. In-situ SMT images were processed to produce 3D meshes that accurately resemble the complex morphology of the natural sand particles. A material point user-subroutine was developed and implemented in ABAQUS to simulate the constitutive and fracture behaviors of the 3D meshed particles. The user-subroutine incorporates the anisotropic linear elastic behavior of silica mineral and models particle fracture using the principles of continuum damage mechanics. In single-particle crushing, the fracture stress of the sand particle was mostly dependent on the nature of contact between the particle and loading platens. The fracture pattern of the sand particle was mainly influenced by microstructural imperfections and the direction of loading relative to the crystal lattice orientation of the sand particle. In confined 1D compression, the fracture stress of the sand particles correlated well with the particle coordination number and the aspect ratio. Sand particles within the specimen were found to fracture at higher stress levels when they established more contacts with their neighboring particles and exhibited mostly spherical shapes rather than elongated ones. The paper demonstrates the fundamental contribution of micro- and crystalline-scale properties to determine the constitutive and fracture behaviors of silica sand particles.

The purpose of this study is to examine the behavior of simple soil slopes reinforced with geosynthetics using deterministic and stochastic as well as circular and noncircular limit equilibrium method (LEM) of slope stability analyses. Two particular types of stochastic analyses, namely single random variable analyses and spatial variability analyses based on the random limit equilibrium method (RLEM), are performed in order to render probability of failure (P_f). Bishop’s method is used as the circular LEM approach, and the GLE/Morgenstern-Price method together with a global metaheuristic optimization method (Cuckoo search) and a local optimization technique (surface altering optimization) are then used as the noncircular RLEM. Three different failure mechanisms (external, internal, and transitional) are defined in this study. The threshold values of the reinforcement length and tensile strength are presented for both the external and internal failure mechanisms. Contour plots are drawn with noncircular slip surface assumption for different deterministic F_S values corresponding to the external, transitional, and internal failure mechanisms as introduced by previous researchers. This investigation evaluates, for the first time, the stochastic F_S values for the geosynthetic-reinforced slopes with the noncircular slip surface assumption using LEM, with and without spatial variability. Finally, relevant stochastic design charts for a wide range of the deterministic (mean) F_S and internal friction angles are presented for the external and internal failure mechanisms.

In the present paper, the modulus of subgrade reaction or subgrade modulus for sand–clay layered soil (granular fill over clay) with or without geogrid reinforcement is determined under vertical loading by a series of model-scale plate load tests (PLTs). Various parameters such as thickness of the sand layer over clay, shape and width of the test plates, number of reinforcement layers, and spacing between two closely spaced plates (to simulate the interference effect of foundations) are included in the study. Five model plates with different aspect ratios (length to width ratio, L/B) are used to investigate the effect of aspect ratio and width of the plate on modulus of subgrade reaction for layered soil. The modulus of subgrade reaction for unreinforced soil increases significantly when the sand thickness increases over clay even if the thickness is more than twice the width of the test plate. However, marginal increment in modulus of subgrade reaction is observed when the sand thickness to plate width ratio is greater than 1.25 for geogrid-reinforced sand–clay layered soil. The maximum improvement in modulus of subgrade reaction due to inclusion of geogrid is observed when the thickness of the granular fill over soft clay is 0.75 times the width of the test plates. For an unreinforced bed, the modulus of subgrade reaction can be reduced up to 16% due to interference effect when the spacing (S) between the plates is less than 1.33 times the width of the plates. For reinforced sand–clay bed, 12% reduction in subgrade modulus can occur due to the interference effect. The subgrade modulus decreases with aspect ratio of the plates for both single and dual plate cases.

The recently developed framework for modeling grain breakage in granular materials is shown to be valid for saturated/unsaturated conditions. The model describes the initiation, development, and stabilization of breakage using three parameters, all depending on the strength of a representative particle size. When water is introduced, the strength of the soil's particles is expected to weaken, which leads to increased breakage intensities. The model is able to predict the early onset of crushing and the increase in particle breakage rate, both considered characteristic behaviors of a crushable granular medium in wet conditions. Initially dry and saturated model lines limit the evolution of the model parameters in the intermediate saturation states. A mid-loading change in the saturation of the granular medium results in an increased rate of particle breakage. The experimental data available in the literature is analyzed in light of the proposed model, which allows a better understanding of the development of particle breakage under the influence of water.

Expanded polystyrene (EPS) geofoam is commonly used as lightweight fill materials in wide range of geotechnical engineering applications including protection of buried utilities and pipelines. EPS blocks are usually placed next to buried pipelines to reduce the overburden and traffic-induced pressure on them. In this paper, a new configuration of EPS blocks around the buried utility is defined and its performance under traffic loading examined. The proposed configuration consists of three buried EPS blocks. Two blocks (posts) are vertically oriented, while a capping EPS block (beam) is placed atop, leaving a void to protect the buried utility. Finally, soil cover is placed and compacted above the beam. By considering sufficient void space, the protection system will carry all the imposed load, and no stress will be incurred to the protected utility. The effects of beam thickness, soil cover thickness, EPS density, free span length between the posts, and soil cover reinforcement on the system's behavior under cyclic loading were explored through large-scale laboratory model tests. System performance enhanced when high-density EPS blocks, thicker beam and soil cover were used. The results also showed that reinforcing the soil cover with a single layer of geogrid could significantly lower the blocks' deformations and control their dynamic strain rate under cyclic loading. Finally, a three-dimensional finite-element model was developed, validated against experimental results, and used to gain more comprehensive insight into the protection system's performance under loading.

Engineers often face the challenge of constructing on soft soils that are associated with low bearing capacity and severe post-constructional settlements. In the subsurface zone, volume-change behavior of saturated soft soil is important in predicting the potential settlements. In this study, laboratory experiments have been conducted to monitor densification and consolidation processes of two soft geomaterials under incremental surcharge loading. During these experiments, densification of the geomaterials have been evaluated through a noninvasive scheme using electromagnetic (EM) methods. For this purpose, a time-domain reflectometry (TDR)-based approach has been accomplished by means of rod probe sensors. Changes of TDR waveforms under several surcharge loadings have been analyzed to establish soil properties, such as dielectric permittivity, volumetric water content, density, and porosity. Translating this laboratory-based nondestructive monitoring scheme to the field would potentially facilitate in management of ground improvement trials prior to, during, and after construction on soft soil deposits.

The performance of large diameter pipes under construction loads is inherently coupled with knowledge of the complex soil–pipe system. Current methods do not cover all the different combinations for material, trench width, and native soil properties, and were developed based on limited experimental studies. In this work, a comprehensive parametric study using nonlinear finite-element analysis was conducted to predict the deformation and forces of buried large diameter steel pipes during construction. Different parameters, including pipe diameter, diameter-to-thickness ratio, soil properties, trench width, and burial depth, were considered. Results were used to develop equations inspired by the modified Iowa formula to estimate changes in pipe diameter and internal forces during construction that directly include the mechanical properties of the pipe, embedment, trench, and backfill material, as well as the pipe and trench dimensions and the applied loads. They were further validated by estimating the available data from previous studies with acceptable accuracy. These equations can act as a tool for engineers to calculate the desired outputs, without the need for a sophisticated finite-element analysis program.

Field measurements and laboratory tests were carried out to study the mechanical behaviors of soil in response to earth pressure balance (EPB) shield tunneling in mixed-face conditions, i.e., layers of granite and sand. Specifically, an experimental investigation was carried out using a laboratory-scale model to replicate the EPB tunneling operations in such ground conditions. The effects of the ratio of rock/sand at the tunnel face (T_r/T_s) and the cover-to-diameter ratio (C/D) on the soil pressure in the chamber, ground displacement, and volume loss were examined. The results show that the soil's response to the mixed-face conditions differs significantly from that in the homogenous ground and highly depends on the ratio of rock/sand, especially for relatively shallow tunnels. As the ratio of rock/sand at the tunnel face increased, the pressure gradient in the chamber became more inconsistent. The translated cumulative curve does not always provide a good fit in the mixed-face conditions, particularly in cases when the rock/sand ratios are high. A smaller width of settlement trough has been observed for cases with a large rock/sand ratio compared to that in clay and cohesionless soil.

The numerical simulation of a 3D complex reservoir has been an important but difficult problem. One of the biggest challenges is how to deal with the large number of natural fractures with consideration of hydromechanical coupling effect in those fractures. To address this problem, a 3D hydromechanical coupled element partition method (3D-EPM) is developed. The 3D-EPM allows a fracture to run through an element without any extra degree of freedom. It can embed any number of fractures in a background mesh without mesh modification. This brings great convenience to 3D reservoir simulation. To represent the permeability of a cracked element, the equivalent permeability of this cracked element is derived based on the cubic law. To account for the hydromechanical coupling effect in a fracture, the coupled equation of 3D-EPM is developed. It is verified by the analytical model. The simulation results suggest that this method can simulate the 3D hydraulic fracture propagation, its interaction with natural fractures and the impact of in-situ stresses. This paper provides an alternative method for the 3D hydraulic fracture simulation in a complex reservoir with consideration of hydromechanical coupling effect in a fracture.

Weak subgrade condition generally develops large settlements in ballasted tracks, leading to adverse performance. To ameliorate such problems, a commonly adopted technique is to provide a thick cushion of granular subballast/blanket over the subgrade. Owing to scarcity of natural resources, this is often a costly proposition. In the present study, application of geogrid reinforcement for possible reduction of the subballast thickness has been explored through large model plate load tests. The investigations include both single and multiple layers of reinforcement in the subballast. With geogrid reinforcement, stiffness and resiliency of track beds were found to have increased markedly. Optimum depth of single-layer geogrid in the subballast giving maximum performance improvement was about 0.33 times the loading diameter. The corresponding improvement in stiffness of the track bed was about 77%. With multiple layers of geogrid in the subballast, the improvement in stiffness was as high as 99%. It is observed that with just one layer of geogrid in the subballast, its thickness can be reduced by 33% (i.e., from 600 to 400 mm).

The foundation bearing-capacity characteristics and differential settlement have become the vital issues of high-speed rail study. Because of the collapsibility around loess foundations, the bearing characteristics as well as differential settlement are significantly different from other soil foundations. At present, there are many studies on other types of soil foundations, while the bearing capacity characteristics and differential settlements of the column-hammered and thrusted-expanded pile (CHTEP) composite foundation in the collapsible loess area are rarely involved. Therefore, based on the current codes, field tests and finite-element method (FEM), the variation in the differential settlement and bearing capacity characteristics of composite foundations with CHTEP is studied in collapsible loess areas. This paper mainly obtains the changing law of pile body stress, pile–soil stress ratio, pile side-friction resistance, differential settlement about the pile, and the soil between the piles of the composite foundation with CHTEP during different construction conditions. The result also shows the bearing capacity and settlement about composite foundation with CHTEP is up to code. This paper can provide some important rule to the design or construction about composite foundations with CHTEP at collapsible loess areas or other similar cases.

In this study, analysis of real-scale field pile loading test results on 20 fully instrumented steel pipe test piles will be carried out, to propose a modified empirical formula to estimate the bearing capacity of the steel pipe prebored and precast pile. In addition, to overcome the limited consideration of the surrounding soil capacity of the existing formula, the proposed formula will be based on an expanded standard penetration test (SPT) N value that will consider the realistic conditions of the ground. The formula will be proposed based on a statistical approach to the data points from the field pile loading test, to ensure safe engineering practice and find a reliable formula. The statistical analysis of the data points indicated that the existing formula underestimated the bearing capacity of the steel pipe prebored and precast pile. The proposed formula estimated a 20% higher pile tip bearing capacity and shaft resistance compared with the existing formula. The accuracy and the stability of the proposed formula will be verified by comparing the estimated results with additional field test data. The verification process showed that the proposed formula gave more realistic results and did not exceed the actual bearing capacity of the test piles.

This paper analytically investigates the postconstruction load-carrying capacity of a cast-in-place pile in clayey soil. The stress release induced by borehole excavation, the slurry supporting effects, and the dissipation of the negative excess pore-water pressure after construction, all of which have significant effects on the effective stresses of the soil around the pile, are the main concerns of this study, which aim to establish a method to reasonably evaluate the load-carrying capacity of a cast-in-place pile after construction. The stress release due to borehole excavation is modeled by cylindrical cavity contraction theory, which employs a K₀-consolidated anisotropic modified Cam-clay (K₀-AMCC) model to represent the mechanical behavior of the soil. Considering the dissipation of the negative excess pore pressure, the load-carrying capacity after construction is determined by the total stress method, with consideration of the three-dimensional strength of the soil adjacent to the pile. The proposed method was verified by finite-element (FE) numerical simulations. The results indicate that the soil properties and the factors involved in pile construction, such as the stress release due to borehole excavation, the slurry supporting effects, and the dissipation of negative excess pore-water pressure, have substantial influences on the postconstruction load-carrying capacity of the pile.

In this study, the Taguchi design of experiments (TDOE) is employed to enhance the bearing capacity of geotechnical structures. To this end, two different case studies, including tapered helical piles as a novel kind of deep foundation (Case 1) and a shallow foundation resting on braid-reinforced soil as a new type of soil reinforcing technique for shallow foundation beds (Case 2), are studied. A series of large-scale tests, including pile loading tests in frustum confining vessel (Case 1) and standard plate load tests in test pit (Case 2), have been conducted in conjunction with numerical analyses. To the best of the authors’ knowledge, this study is the first of this kind that uses the capability of the TDOE method to evaluate and improve the bearing capacity using large-scale tests. After conducting the tests, analysis of signal-to-noise, analysis of means, and analysis of variance were used to interpret the experimental results, to obtain the optimum condition, and to determine the percentage of each factor’s participation in bearing capacity. Moreover, the Taguchi method output predictions are compared with the test observations and numerical modeling results. The comparison between test results and TDOE method predictions confirms that the Taguchi method can predict the bearing capacity well (R² > 0.95). Additionally, verification tests on optimum models show a low level of relative error (RE < 5%) between the TDOE predictions and test results for both the case studies. Therefore, the results prove the ability of the TDOE method to predict and determine the optimum condition in geotechnical bearing capacity problems.

This study mainly focuses on the transport process of broken rocks in geological fractures, faults, and karst conduits. Because previous research mainly focused on the influencing factors of adverse geological conditions, there is no clear understanding of the migration behavior of fillings and the formation process of pathways in the process of water inrush. An experimental testing apparatus was designed and developed to perform systematic research on the transport process of granular soils subjected to seepage flow. This system was comprised of a water supply system, acrylic glass holding device, and collection system, which could effectively be used to study the influence of discontinuous gradation and flow velocity on the permeability characteristics of loosening fillings. The experimental results show that the water inrush induced by seepage failure results from the gradual migration and loss of particles by water seepage. According to the fine-grain content and loss characteristics of the samples, the samples are divided into three types: those with a nonskeleton structure, with a dense-suspension structure, and with a void-skeleton structure. With an increase in the content of fine particles, the porosity and permeability decrease whereas the time required for water inrush of the sample gradually increases. With an increase in flow velocity, the time required for water inrush and its rate of change gradually decrease. However, the mass loss of particles does not increase with the increasing flow velocity during the same period. The research results provide a valuable reference with which to further study the mechanism of variable mass seepage in faulted and fractured rock.

For a vertical plate emerging on the surface of undrained cohesive soil, the adhesion between the plate and soil considerably impacts the lateral soil pressure on it. However, very few closed-form solutions have been published to address this seemingly simple problem; they either are restricted to certain conditions or overpredict the ultimate lateral pressure. This paper applies both the lower-bound and upper-bound methods of plasticity to develop a rigorous analytical solution to the ultimate lateral pressure, allowing for the undrained shear strength of soil to increase linearly with depth and a general adhesion on the interface. A method is presented to extend the static stress field throughout the soil mass to validate the lower-bound values. The developed solution is found to be an exact solution for homogeneous soil; the predicted results for nonhomogeneous soil fall within a narrow range bounded by the lower and upper limit values, with the range of errors mostly being within 1%. The solution reduces to the classic Bell’s relationship in the undrained condition if ignoring the adhesion on the interface. When the full active pressure behind the plate is mobilized, the upper-bound solution is rigorous but the lower-bound one is not unless examining a smooth surface. However, the predicted results are close enough to more rigorous ones to be used in engineering practice.

Piles are sometimes unavoidably embedded in slopes for supporting buildings on hills. In contrast to a pile on a horizontal ground, a pile in slope is acted on by additional sliding force from the slope, impairing its load-bearing capacity and buckling resistance. Nevertheless, proper assessment for the buckling of piles in slopes is difficult because of the simulation of distributed sliding forces and nonlinear pile–soil interactions. This paper refines the newly developed Euler–Bernoulli pile element formulation for the nonlinear buckling analysis of single piles in slopes by including the sliding force in element formulation, enabling a rigorous consideration of soil–pile interactions. Detailed mathematical derivations are provided. The numerical implementation is illustrated with a flowchart. Four examples for verification are demonstrated to reveal the robustness of the proposed method and the importance of considering the sliding force.

The facing design of soil nail walls against flexure, punching shear, and headed-stud tensile limit states has been rarely studied within the reliability-based design framework. This study presents reliability analyses of both temporary and permanent soil nail walls against facing limit states using the default and improved Federal Highway Administration (FHWA) facing load models and the default FHWA resistance models. With consideration of model uncertainty and variability of soil shear strength, reliability analyses are conducted on the facing that is first designed to achieve a set of prescribed factors of safety using conventional deterministic allowable stress design approach. Results show that the current deterministic design practice typically leads to a facing design with minimum reliabilities of 1.0–2.5 against the limit states. A factor of safety of 3–4 is warranted for a minimum reliability of 3.54. The punching shear limit state has the least reliability. Statistical correlations among the limit states are investigated and the facing system reliability is evaluated, where system reliability is defined as the reliability that none of the three limit states is reached. Finally, sensitivity analyses are carried out to examine the influences of several design parameters on the computation outcomes of reliability.

The excessive load from the high embankments of high-filled cut-and-cover tunnels (HFCCTs) threatens the safety and stability of HFCCTs. Relatively low-compacted (RLC) soil can reduce such loads in the short term, but the long-term ability of RLC soil to reduce the load on HFCCTs is unknown. The changes in the soil arching effect that are resulted from soil creep needs to be considered carefully in HFCCT design. Three stages of analysis were conducted in this study: immediately after backfilling (0 month), during backfill creep, and after the soil deformation has stabilized (240 months/20 years). A finite difference program, FLAC3D, was employed to investigate the soil’s vertical earth pressure and displacement distribution around a cut-and-cover tunnel (CCT). The Burgers model was used to simulate the creep behavior of the soil. In addition, parametric studies for different dimensions and locations of RLC soil were conducted. The results show that the soil arching effect that is due to the inclusion of RLC soil works well initially to reduce the load but eventually disappears, which can result in a significant load rebound greater than 100 kPa and jeopardize the stability of the HFCCT.

Meadow soil is rich in fresh plant roots and differs considerably from general soft soil in terms of its engineering characteristics. Previous studies have shown that reticulated roots can produce a reinforcement effect and thus improve the overall bearing capacity of foundations. In accordance with the actual conditions of the Tupo Highway Project, Xinjiang, China, the meadow soil for the model test was prepared by employing similarity theory. The model box tests of 0, 1, 3, and 6-cm meadow soil on soft soil foundation were performed. The distribution of the vertical additional stress under the highway and the settlement of the foundation at different locations were measured. It was verified that the meadow soil foundation undergoes an evident stress diffusion effect, which can effectively reduce the vertical additional stress and settlement in the foundation. However, it would also increase the distribution area of the additional stress. Finally, according to the stress distribution characteristics of the meadow soil foundation, a calculation method for determining the ultimate bearing capacity of a meadow soil foundation was developed. The calculation results were found to closely agree with the measured values.

This research will investigate the numerical simulation of rockfill materials using a combined scaled boundary finite–discrete element method (SBFEM/DEM) with two breakage models. Two rockfill specimens that are subjected to biaxial compaction will be simulated. The influence of breakage on the macroscopic stress–strain behaviors will be investigated by comparing the results obtained when breakage and no breakage were considered using two different models. Further investigations will be carried out to identify the effect of particle breakage on the stress–strain relationship, particle size distribution (PSD), and the force chain transmission of the rockfill specimens under different breakage models. The simulation with Breakage Model 2 (BM2) generated more small particles than when Breakage Model 1 (BM1) was used; therefore, it had the lowest shear strength, the most contractive behavior, and the lowest interparticle contact forces. Because one particle will be crushed into many small particles in practice, BM2 was recommended as the first option.

Unsaturated soil is widely distributed in geotechnical projects, of which the consolidation and settlement are of great importance. Based on the consolidation theory of unsaturated soil, proposed by Fredlund and Hansan, this paper deals with one-dimensional consolidation of single-layer unsaturated soil with six types of boundary conditions, which can be denoted by arbitrary specified time-dependent functions. The analytical solutions in the time domain are provided directly, by homogenization of nonhomogeneous boundary conditions and the eigenfunction expansion method. Until then, the solutions for excess pore-water pressure and excess pore-air pressure in the single-layer unsaturated soil with all possible Dirichlet or Neumann boundary conditions are provided. Finally, the analytical solutions in this paper are validated against published results, and responses of excess pore-water pressure and excess pore-air pressure in the soil layer subjected to different time-dependent boundary conditions are investigated.

In the past, the capillary effect is rarely considered for microcontact models when two adjacent particles are separated by a certain distance. In this paper, a liquid-bridge contact model of unsaturated particles is presented, which is applied to the discrete-element software PFC. Based on this, simulations of uniaxial tensile for unsaturated soils under (2D) situation are carried out, and influence of a water retention angle on uniaxial tensile strength are studied. The simulation results show that the uniaxial tensile strength of unsaturated soil decreases gradually with the increase of the water retention angle, obvious cracks generate at both ends of the soil samples, and the soil sample possesses a residual strength. According to the particle displacement field, velocity field, and contact force chain, the failure forms of samples with different water retention angles are determined. Based on the rose diagram of normal contact force, the changes of its direction and value during failure process are observed directly, so as to analyze the evolution law of contact force for unsaturated soils.

Soft marine deposits are widely distributed in the coastal region of China. The marine soft clays have high water content and high sensitivity, which shows high compressibility and low strength. The installation of precast piles for wind turbines over soft marine clay will generate high excess pore water pressure (EPWP) with very low dissipation rate, resulting in low bearing capacity and large postconstruction settlement, which will affect long-term stability. This study investigated the generation and dissipation of the EPWP correlated with the change in soil structure during the installation of pile foundations in a project of 100 MW wind-power generation in Lianyungang, Jiangsu, China. The results show that the marine soft clay soils feature strong natural structures based on the intrinsic compression concept. The EPWP decreases with increasing distance from the pile, whose influence reaches a distance of 6 m (about 10 times the pile side length). The structural strength of natural sedimentary clay has a remarkable impact on the generated EPWP. The dissipation rate of the EPWP is very slow in mucky clay with more than half the residual value after 30 days, which is mainly attributed to the sharp decline of consolidation coefficient induced by the disturbance of natural clay soils from pile driving. Moreover, hydraulic fracturing can well explain the dissipation characteristics of the EPWP in clay. This phenomenon is actually an ongoing process especially in marine soft clay soils with a strong cementation effect.

Soil conditioning technology is commonly applied to prevent mud caking and soil clogging in earth pressure balance (EPB) shield tunneling and to ensure continuous and efficient construction in highly viscous clay and weathered mudstone strata. In the note, the properties of soil conditioning agents and their interactions are investigated through a series of experimental tests and field construction applications in Changchun Metro Line 2, China. Tangential adhesion tests are carried out to learn the adhesion strength and the torque change relationship between the soil and the metal disk, by which the soil conditioning effect is evaluated. The results indicate that there is a certain interaction between the commercial foam agent and the customized anticlay agent and that the foam agent solution’s concentration and anticlay agent amount play an important role in determining the foam expansion ratio (FER) and the half-life time (HT). When the foam agent solution’s concentration is low, the anticlay agent can increase the FER and decrease the HT. When the foam agent solution’s concentration exceeds 4%, an opposite pattern is observed. It is also found that the composite application of an anticlay agent and a foam agent can significantly decrease the torque and adhesion strength of the weathered mudstone. Torque and adhesion strength can reflect the adhesion of chemically conditioned soil better than the consistency index, which has a good effect on the evaluation of unconditioned soil. Finally, field implementation indicates that mud caking and soil clogging were avoided by the application of the two conditioning agents in the EPB shield tunneling construction of Changchun Metro Line 2, China, and the thrust and torque of the shield were reduced.

Slope stability has always been a concern of the geotechnical engineering community, and geotechnical scholars have continued to explore the reasonable failure mechanism of slopes and make the theoretical models of slope stability more reliable. This work established a novel model for limit-equilibrium (LE) analysis of slope stability with a nonlinear strength criterion. In this theoretical model, the thrust line of interslice force and corresponding increment are reasonably simplified. Then, the formula of normal stress on slip surface is derived by assuming the increment of normal interslice force. Meanwhile, strength reduction technology is applied to reduce the shear strength of the geotechnical body on the slip surface with slope factor of safety (FOS) to obtain shear stress on the slip surface. Thereafter, mechanical equilibrium conditions satisfied by the whole slope sliding body and newly introduced equation about increments of interslice force are used to solve LE stability of the slope. For stability analysis of a slope with a nonlinear strength criterion via a simple and feasible calculation process, an iterative loop solution strategy is adopted in the analysis. After comparison and analysis of several slope examples, the feasibility and rationality of the present method are verified. Moreover, the present method has high efficiency in terms of calculation speed.

Columnar jointed rock mass (CJRM) has a special joint structure formed during the cooling of lava. The self-oriented joint structure can induce mechanical anisotropy of the rock mass, which poses a challenge for geotechnical engineering. To understand the mechanical properties of CJRM, conventional triaxial compression tests were conducted on the artificial CJRM specimens. It can be found from the experiment results that the orientation of columns has a distinct impact on the strength and deformation modulus. Four failure modes of CJRM specimens at different dip angles of columns under different confining pressures can be observed. The anisotropy degree in strength and deformation modulus is estimated, where it is found that the increase of confining pressure decreases the anisotropy in strength and increases the anisotropy in deformation modulus.

A completely decomposed granite (CDG) soil containing a significant amount of sand and silt was tested on a triaxial apparatus to determine whether it complies with the critical state framework or shows a transitional behavior. The test results revealed that the parallel normal consolidation lines (NCLs) and the critical state lines (CSLs) can be identified in the volumetric plane, whose position depends on the initial specific volume of soil at the time of its creation. Various stress paths, including drained preshearing before undrained tests, did not alter this behavior. The distance between each NCL and its corresponding CSL was found to be fixed. However, a unique CSL was found in the q−p′ plane with a gradient of 1.38, and the stress ratios of soils at the end of the test did not show a clear trend with the initial density. The paths of undrained tests showed dilative tails, and even preshearing failed to eliminate these tails. This is another feature of this transitional soil, which may be due to initial fabric. In addition, the compression characteristics and shear behaviors of some other CDG and completely decomposed volcanic (CDV) soils in the previous studies were compared with those of the CDG soil in this study to show the similarities and differences.