International Journal of Geomechanics

Internal erosion by piping causes failure in earthen structures by widening the preexisted cracks that eventually lead to the breach formation being subjected to seepage. This complex behavior was studied by developing a new experimental device named groove erosion apparatus. Until now, the cohesive sediment detachments have been mostly modeled by using a linear excess shear stress approach. A recent study has shown limitations in predicting the erosional behavior of all soils with the available approach because of the varied soil response during erosion while modeling cracks. Therefore, the nonlinear excess shear stress and Wilson models came into the literature. Hence, an attempt was made to identify the reliability of both linear and nonlinear models and to measure the critical shear stress and erosion rate index of different soils at different water content values. It was observed that with the increase in fines the critical shear stress of the soil increases almost linearly for excess shear-stress models. However, the erosion rate index showed different trends when plotted against percentage of fines for linear and nonlinear models. Mutiregression analysis was employed to establish the relation between critical shear stress and engineering properties of soil. Results suggested that no single model can predict the erosional behavior for all soil types.

Recent investigations have opened the prospect of using stone columns in collapsible soils through the use of geofabric encapsulation. However, the effectiveness of this type of ground improvement in such soils is still inconclusive. The main objective of this paper is to investigate the geotechnical performance of encapsulated and stabilized sand columns installed in a collapsible soil layer and subjected to full saturation. Fully penetrating sand columns, encapsulated in a geofabric and stabilized with some cementing agents, were tested. A Terram T3000 geofabric was used as the encapsulating material. The cementing agents used were lime, lime with fly ash, and cement. They were used in different proportions, in this case 4%, 8%, and 12%, respectively. The carrying capacity and settlement characteristics of the reinforced and stabilized columns were examined. Furthermore, analytical models were developed to predict the carrying capacity and settlement of encapsulated and stabilized sand columns. Validation of the developed models with the experimental results of the present investigation and with some data reported in the literature was also considered.

The anisotropic shear strength of rough joints is examined from both experiments and numerical simulations in this paper. The rough joints in the experiment are prepared by combining 3D laser scanning and 3D printing technology. The direct shear tests are conducted in eight shear directions under constant normal load condition (CNL) with the normal stress of 0.2, 0.5, and 1.0 MPa. The dramatic variation of shear strength in different shear directions is observed from experimental results. Meanwhile, the numerical simulation based on the three-dimensional discrete-element method (DEM) is conducted, in which, the method to generate the identical rough joint by connecting triangular walls is proposed. With the calibrated microparameters from the unconfined compression test and direct shear test, the anisotropic shear strength is also observed in the numerical simulation, which is consistent with the experimental result. Accordingly, the topography anisotropy of the rough surface is analyzed, and the statistical parameter, $Z_2^{\theta }$, is found closely related to the anisotropic shear strength of rough joints. Based on this, the Barton model is modified to estimate the shear strength of artificial joints with an anisotropic effect involved.

Cement is often used to stabilize soft clay; however, it has some limitations in increasing clay strength and improving clay failure mode. To solve this, two different additives, i.e., polypropylene fiber and nano-Magnesium Oxide (MgO), were tested with the purpose of improving the mechanical performance of cement-treated soft clay. Four groups of samples with different mixture ratios of coastal soft clay, cement, fiber, and nano-MgO were first designed. Microscopy tests including X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS), as well as unconfined compression test was then carried out. XRD and EDS test results show that the cement hydration reaction is the main source of strength increase and the nano-MgO can generate Magnesium Silicate Hydrates (M-S-H) gelation, which helps to fill the pores of the clay and increase clay compactness. The unconfined compressive strength test results show that adding fiber or nano-MgO alone has a poor effect on the strength improvement for cement-treated clay with high water content. However, adding both additives lead to a significant increase in the clay’s unconfined compressive strength, which is verified by the microscopic observation of clay compactness in SEM images. Moreover, the fiber is found to increase the ductility of cement-treated clay based on the observed failure modes of modified samples.

Piled raft foundations (PRFs) below stepped high-rise towers are often subjected to nonuniform triangular-shaped loads with eccentricities. In this study, 20 rectangular piled rafts with different pile configurations and orientations, embedded in medium-dense sandy soil, are analyzed using three-dimensional nonlinear finite-element (FE) analysis in which the critical state–based Clay and Sand Model (CASM) is used as the soil constitutive model. Different triangularly distributed loads with and without eccentricities are considered in addition to uniformly distributed loads. A systematic parametric study is performed by varying the different design parameters based on which the PRF behavior is systematically investigated in terms of multiple performance parameters such as maximum settlement, differential settlement, angular distortion, tilt, and load distribution between the raft and the piles and between the individual piles. It is observed that the pile diameter, number of piles, and raft plan area control the differential settlement, angular distortion, and tilt the most. Based on the insights gained from the parametric study, a design optimization exercise is performed, in which the most optimal pile configuration is selected based on the criteria of allowable settlement and angular distortion with additional considerations for tilt, load distribution, and the volume of concrete required.

Previous studies have given little consideration to the influence of the soil unloading effect on compaction grouting. The theoretical relationship model between the soil unloading degree and the soil deformation modulus is first derived and verified. A compaction grouting diffusion model considering the soil unloading effect is proposed based on the previous soil unloading model, cavity expansion theory, and Unified Strength Theory (UST) under large strain conditions. The compaction grouting model is compared and verified with other theoretical models. The formula of ultimate compaction grouting pressure is established, and the analysis results show that the ultimate compaction grouting pressure P_u increases with increasing soil cohesive force c, soil internal friction angle φ, soil dilatancy angle ψ, soil initial static pressure p₀, and soil intermediate principal stress coefficient b. A parametric study with the proposed model is performed, and the characteristics of grout bulb diffusion and soil plastic zone development and the distribution of stress and displacement fields in the soil are analyzed.

The influence of the variation in the principal stress direction on the anisotropic and noncoaxial behavior was investigated through several hollow cylinder apparatus (HCA) tests that were performed on reconstituted soft clay specimens under a stress path with a fixed or continuous rotation of the major principal stress axis. In particular, the varying amplitude of the deviator stress (q) and intermediate principal stress coefficients (b) were focused upon. The results indicated that the shear stiffness and strength were strongly dependent on the fixed major principal stress angle. Furthermore, apparent noncoaxiality was observed between the orientations of the major principal strain increment and the major principal stress. Consequently, the noncoaxial behavior of the reconstituted soft clay was sufficiently and effectively described using rose and polar diagrams. Furthermore, the data fluctuation indicated that the noncoaxiality of soft clay was strongly dependent on both q and b during the pure principal stress rotation (PSR). The results obtained for undisturbed clay and sand are not expected to be applicable to reconstituted clay, because its behavior is in contrast to the former two. Regarding reconstituted soft clay, the degree of noncoaxiality was observed to increase during the second rotation (N = 2) compared with that during the first rotation (N = 1). However, this trend gradually weakened with an increase in q or b values. Moreover, regardless of whether N = 1 or 2, the degrees of noncoaxiality decreased with the increase in q for b = 0.5 whereas it increased with the increase in b values for N = 1. However, those for b = 1 were the smallest for N = 2. The results are expected to provide an experimental basis for the constitutive modeling of soft clay with fixed and continuous rotations of the major principal stress axes in ocean engineering.

The current practice for estimating the penetration resistance of suction bucket foundations requires breaking down the penetration resistance into tip and skirt resistance components. Cone penetration test (CPT)-based methodology correlates these components to the cone resistance measurements through empirical coefficients. In this study, an experimental campaign involving suction installation, jacking, and pullout tests on suction buckets with a large aspect ratio (i.e., L/D = 1, where L is the skirt length and D is the diameter) atop sand deposits of varying relative densities was performed to identify the important factors that are involved in the installation procedure but are not well understood. The following factors were studied: the influence of the friction area in caissons of round and modular shapes, the dilative behavior of sand, the soil–structure interface friction angle, and the penetration depth. The experimental results of the jacking installation tests indicated that a larger friction area significantly increased the penetration resistance; however, this effect was completely diminished when foundation suction-assisted penetration was used. Based on these results, modified friction resistance and tip resistance factors in the empirical expressions accounting for the relative density and penetration depth were proposed. Finally, the required suction pressure was back-analyzed by utilizing these empirical relations, reduction factors, and the critical pressure.

Investigating the in situ stress field is one of the primary tasks of the tunnel disaster prevention and design stage in a high geostress environment with a strength–stress ratio lower than four. Due to the limited measured data, inversion is the most mainstream method to obtain the in situ stress field in engineering areas. After discussing the influence of the tunnel longitudinal dimension effect on the inversion accuracy, this paper proposed a segmented single-borehole inversion (SSBI) method that uses multiple regression models to characterize the in situ stress field of the tunnel. This method was applied to four deep-buried (467–1,780 m) and super-long (7.2–16.3 km) tunnels in Southwestern China, and the distribution characteristics of the in situ stress field along the tunnel axis in the fault stratum and intrusive rock stratum were analyzed. The results showed that the SSBI method with several regression models had a higher inversion accuracy than the traditional multiple-boreholes inversion (MBI) method with one regression model, e.g., the inversion error decreased from 12.7% to 6.0% in the Muzhailing tunnel, and the inversion error decreased from 30.7% to 6.3% in the Lanjiayan tunnel. Furthermore, the average relative error between the calculated values and the measured values not involved in the inversion was 11.0%, verifying the reliability of the proposed method. The inversion of the in situ stress field in two tunnels with special strata showed that the magnitude and orientation of the in situ stress at the boundaries of the intrusive rock and the fault had changed drastically, and its distribution characteristics had a certain regularity.

Roadways with low embankments may undergo considerable postconstruction settlement under traffic loads, which can significantly threaten roadway safety. This study aimed to investigate the dynamic response of a low embankment subjected to moving traffic loads on Yangtze River floodplain soils. Dynamic earth stress sensors were installed to monitor the dynamic responses at different depths. Heavy and light vehicles were allowed to drive over these at speeds ranging from 20 to 80 km/h. To verify the effect of pavement thickness, field tests were conducted at two different stages in roadway construction. The spatial distributions and transfer mechanisms of dynamic stress under moving traffic loads were examined through measured data. In addition, a three-dimensional finite-element model was established to further analyze the vertical acceleration and displacement caused by dynamic traffic loading. The results indicated that, with the completion of a semirigid subbase, the significant-influence depth was about 1.6 m under the heavy-vehicle load. In contrast, the dynamic stress became negligible in the upper subgrade layers after completion of the pavement structure, indicating the dominant role of the pavement structure in dispersing dynamic stress. The dynamic responses intensified with increasing magnitude of vehicle load and vehicle speed, but the effect reduced with decreasing pavement roughness. Furthermore, the significant-influence depth of vertical displacement was markedly greater than that determined by dynamic stress.

The trapdoor/trapdoor-like model test has been widely utilized to investigate the evolution of soil arching. However, the primary focus of previous studies has been on the mechanical and deformation behaviors of the arching field under the single-trapdoor condition, while the interaction of soil arching between adjacent trapdoors has not been well understood. In this paper, a series of discrete numerical models based on the plane–strain laboratory trapdoor test were established to investigate the interaction effect, with respect to stress redistributions, particle movement, anisotropy of contact forces, and energy regime. The effects of motion mode, namely the simultaneous and nonsimultaneous movement, and the spacing (B) between adjacent trapdoors on the arching performance were examined. The numerical results revealed that the simultaneous movement of twin trapdoor slightly influences earth pressures resting on the surface of both trapdoors. The deformation pattern is deeply influenced by a narrow spacing of 0.25B and characterized by two arching fields interacting with each other, resulting in a noticeable subsidence at the crest. The subsequent lowering of the second-lowered trapdoor under the nonsimultaneous movement condition increases pressures resting on the first-lowered trapdoor, yields additional settlement within the former arching field, and distorts adjacent arched force chains. An increase in spacing from 0.25B to 1B is beneficial for reducing the pressure increment, decreasing the arching deformations, minimizing the rotation of the major principal direction, and decreasing the friction energy distribution density above the stationary supports.

The depressurization method that is used to produce methane gas can increase the effective stress in hydrate-bearing sediments and induce deformation and settlement of reservoirs, which has adverse effects on safe and stable exploitation. A series of isotropic consolidation and depressurization dissociation tests under high effective confining pressures on methane hydrate-bearing specimens were conducted to investigate compressive characteristics and deformation behaviors. Isoconsolidation test results demonstrated that the rise in effective confining pressure-induced increasing compressibility and particle crushing of sediment, while the presence of hydrates can suppress compressibility and crushing. The compression index tends to increase with increasing effective stress but decrease with increasing hydrate saturation. Dissociation test results suggested that higher effective stress during dissociation and higher deviatoric stress led to more significant deformation and particle breakage. A specimen can exhibit serious deformation (ɛ_v ≈ 20%) after dissociation when the effective stress is extremely high (17 MPa), even if the stress state is in the stable zone. During water recovery after dissociation, axial and volumetric strains may further increase under the combined effect of deviatoric stress and high effective confining pressure.

In this study, systematic investigations were conducted to solidify dredged marine sediments using the low-carbon composite binder made by mixing Ordinary Portland and calcium sulfoaluminate cement (OPC–CSA). A series of tests to evaluate physical and mechanical properties of samples, which indicated that the OPC–CSA composite binder could effectively improve the engineering characteristics of solidified dredged marine sediments, such as the immediate California Bearing Ratio (I-CBR) index, unconfined compressive strength, splitting tensile strength, and elastic modulus. In addition, simple models were proposed to correlate the unconfined compressive and splitting tensile strength with the elastic modulus of treated sediments. Importantly, the elastic modulus of treated sediments was defined by the local small-strain sensor method. In addition, the correlation between the strength and the three kinds of failure mode of the specimens was revealed. Lastly, simplified carbon footprint analysis indicated that OPC–CSA composite binder offers potential CO₂ emissions savings of 14%–41%. The laboratory tests have revealed that the mechanical and environmental behaviors of solidified dredged marine sediments meet the environmental and engineering requirements of the standards and regulations. Low-carbon and sustainable OPC–CSA composite binder-solidified dredged marine sediments could be reused as subbase or roadbed infill materials for low traffic.

Pile foundations are widely used in regions with expansive soils to transfer the loads from superstructures to a rigid soil stratum, thereby alleviating stability and deformation problems. However, current design procedures for pile foundations are typically based on saturated soil mechanics principles assuming drained conditions, despite the fact expansive soils surrounding the piles are typically in an unsaturated state. Volume changes of expansive soil induced by matric suction changes upon seasonal wetting and drying can significantly influence the pile load-transfer mechanisms. In this paper, using unsaturated soil mechanics as a tool, theoretical models are introduced for estimations of pile shaft friction and pile base resistance considering both the influences of matric suction changes and matric suction variation-induced volume changes of expansive soil around the pile. The commonly used shear displacement method for interpreting the pile mechanical behaviors is modified by including these models to extend their application to piles in unsaturated expansive soils. The proposed modified shear displacement method (MSDM) is interpreted and successfully validated using a pile infiltration test conducted in the laboratory along with another case study from published literature. The results of investigation studies using the proposed MSDM suggest that it can be a valuable tool for practicing engineers to make reasonable predictions of mechanical behaviors of piles in unsaturated expansive soils.

The classification and real-time identification of surrounding rock grades are of great significance to guide tunnel boring machine (TBM) construction. Taking a water diversion project in China as the background, this study evaluates the relationship between tunneling parameters, surrounding rock grades, and tunneling performance (TP) using actual TBM tunneling and geological data with the aim to create a novel surrounding rock classification method that is based on tunneling performance. The advance rate and specific energy of excavation are used as the measurement indexes of TBM TP to carry out the surrounding rock classification. The rationality of TP classification is verified by statistical analysis of the distribution of the thrust, torque, rotational speed, penetration, penetration rate, and utilization of surrounding rocks at all TP grades. Furthermore, a cross-validation support vector machine model based on mean interval value backpropagation is used to realize the real-time identification of TP grades, achieving an accuracy of 95%. Finally, the correlation between thrust and penetration rate under the basic quality index (BQ) and TP classification systems is analyzed, respectively. It is found that there is a positive correlation under the TP classification system and a negative correlation under the BQ classification system, indicating that the TP classification system is more suitable for guiding TBM construction than the BQ classification system. The proposed tunneling performance classification method and real-time identification model of TBM tunnel surrounding rocks provide a reference for guiding the safe and efficient tunneling of TBMs.

During tunnel excavations through shale formations in central and southwest China, engineering problems, such as large deformations and distorted arches, were encountered due to radial stress unloading and groundwater pressure. Few studies have been carried out on the issues exhibited by soft shale tunnels that have considered the comprehensive influence of unloading and water effects. To characterize the unloading behaviors, a series of conventional triaxial compression (CTC) tests and unloading confining pressure (UCP) tests were performed under drained conditions and compared. Based on theoretical and experimental analyses, deformation parameters from the UCP process were derived and compared with those from the CTC test. The stress–strain response, evolution of deformation and strength parameters, and postpeak mechanical behavior and failure modes were analyzed in order to reveal the unloading and water effects. To quantify the difference between the CTC and UCP behaviors in geotechnical practice, a tunnel excavation was simulated using the CTC and UCP models. The distributions of damage and displacement were analyzed in a numerical case study. The results showed the comprehensive dependency of shale behaviors on unloading and water effects. The numerical case revealed significant tunnel deformation and fewer plastic zones in the excavation when using the UCP model rather than the CTC model. To accurately simulate the deformation and damage distribution, this study provided a methodology for construction design using the UCP test and the model for unloading and water-affected geotechnical engineering.

The induced trench construction method has been in practice across North America for the last century, and the analysis and design of such structures are conducted in accordance with Marston’s theory and the indirect design method. Recent North American design standards have adopted the Standard Installations for Direct Design approach for the design of rigid culverts, which does not address induced trench installations. In order to advance the state of practice for induced trench design so as to align with modern design standards, it is necessary to first achieve a fundamental understating of their loading conditions as uncertainties remain with regards to the actual distribution of earth pressures around the circumference of induced trench culverts. In this study, finite-element modeling was employed to evaluate the distribution of earth pressures acting on induced trench culverts; numerical modeling techniques were validated with experimental data and parametric studies were performed to investigate the influence of key design parameters for culverts installed in both single and twin configurations. The results of this study suggest that the distribution of earth pressure acting on induced trench culverts differs significantly from that acting on positive projecting culverts and that the interaction between induced trench twin culverts is not insignificant.

In this paper, a thermoelastoplastic constitutive model integrating interparticle bonding is proposed to describe the fundamental thermal and mechanical behaviors for different geomaterials (e.g., soft rock, sand, and clay) within a unified framework. In the proposed model, the concepts of subloading surface and superloading surface are adopted to describe the effects of overconsolidation and structure on the mechanical properties of geomaterials. A state variable characterizing the degree of bonding strength is integrated into the yield function to supplement the description of interparticle bonding effects on the mechanical properties of geomaterials. To consider the effects of temperature, thermal expansion/contraction strain is taken as a part of the total strain, and the bonding strength and structure are correlated to temperature change to describe the mechanical properties of some geomaterials affected by temperature. Except for the conventional thermophysical parameters, the model here employs only eight mechanical parameters, five of which are the same as those in the Cam-clay model. The three additional parameters have clear physical meanings and can be determined by conventional tests. Through the calculation of element tests under different mechanical, hydraulic, and thermal conditions for different geomaterials, it is confirmed that the proposed model here can describe properly the general thermoelastoplastic behaviors for typical geomaterials. Moreover, by calculating a temperature-related boundary value problem (BVP), it is found that under a long-term cycling temperature condition, even thermal expansion/ contraction will cause the degradation of bonding in the soft rock.

The design and construction of concrete face rockfill dams (CFRDs) usually require a rapid and accurate prediction of deformation behavior to support dam optimal design and safety evaluation. Deformation prediction and control are key issues faced in the construction of CFRDs. This study collects measured data of 75 CFRD case histories. On the basis of the statistical review of the typical dam crest settlement behavior of CFRDs, a prediction model for dam crest settlement combining threshold regression (TR) and support vector machine (SVM) is established. A mixed weight coefficient is introduced to construct an adaptive hybrid kernel function with good learning ability and generalization performance. The particle swarm intelligent optimization algorithm is adopted to optimize model parameters for establishing an improved SVM prediction model. To further improve the generalization ability and accuracy of the improved SVM model, the multivariate TR theory is used to segment the dam crest settlement data according to the dam height. Then, an improved SVM prediction model is established in each dam height interval. The comparative analyses of the prediction results of different models show that the TR–SVM model effectively weakens the nonlinear mutation characteristics of the case data and achieves high prediction accuracy.

Concrete cutoff walls are becoming more widely used to control foundation seepage for earth–rock dams built on a thick soil foundation because of the urgent demand for hydroelectric energy. As the lifeline impermeable structure, the safety of the concrete cutoff wall is of great importance and deserves increased attention. However, such walls have often been analyzed through linear-elastic modeling and simulated as a continuous structure. The working behavior of the discontinued concrete cutoff wall with slurry cake is still unclear. This paper presents a three-dimensional (3D) nonlinear finite-element numerical analysis of the concrete cutoff wall in a thick soil earth–rock dam foundation considering the effect of slurry cake. The results indicate that the damage degree and range in the concrete cutoff wall are significantly affected by wall discontinuity and slurry cake thickness. Moreover, the panel joints may open at the downstream side of the wall under the action of lateral water pressure, which will reduce the effective thickness. The joint opening and tensile damage degree decrease with a reduction in panel width, while the compression damage at the lower part of the wall becomes more serious. The thickness of slurry cake should be controlled reasonably because of its obvious effect on damage behavior of the wall. The working behavior of the concrete cutoff wall can be improved by arranging the width distribution of the panel reasonably and dealing with the problem of the slurry cake. This study can provide useful basis and suggestions for the design of a concrete cutoff wall with slurry cake between panels in thick soil foundations.

This paper explores the characteristics of energy accumulation, evolution, and dissipation of sandstone samples under different confining pressure conditions in the triaxial cyclic unloading test. The characteristics of the stress–strain relationship of deformation and failure of rock samples are analyzed in detail. By utilizing the integral method for the area, the densities of total energy, elastic energy, and dissipated energy under different confining pressure are calculated. In addition, the energy evolution laws of rock deformation and failure with cyclic unloading times are researched. The results demonstrate that during the unloading cycle of confining pressure, the total energy density u, elastic energy density u_e, axial total energy density u₁, and axial elastic energy density u_e1 increase, the radial total energy density u₃ and the radial elastic energy density u_e3 decrease, and the dissipated energy density is almost unchanged. The total energy density u and elastic energy density u_e of rock under different confining pressure cycle unloading have a significant linear relationship. Meanwhile, the scanning electron microscope image shows the microstructure characteristics of the cracks in the sandstone samples. The image results are consistent with the analysis of the macroscopic failure characteristics. Under the same stress path, the higher the initial confining pressure, the more severe the failure of the rock sample. The experimental results are expected to enhance the basic research on the energy characteristics under the triaxial unloading behavior of rock.

This study proposes the novel geometrical design of open trenches in contrast to the traditional rectangular type of open trench, in order to improve the efficiency in mitigating the traffic-induced ground vibrations. The novel geometric design involves the variation in cross-sectional shape, cross-sectional area, sidewall inclination, depth of trenches, and the number of trenches. In addition, the efficiency of the multirow trenches with shallower depths, in contrast to the single-row deep trench, is also assessed for further mitigating the low-frequency ground vibrations. It is argued that these novel open trenches would change the wave propagation direction while also weakening the wave propagation capability in the original direction. A two-dimensional (2D) finite-element study is performed to investigate the isolation efficiency of novel open trench techniques with varying cross sections in a linear elastic, isotropic, and homogeneous half-space. A steady-state vertical harmonic excitation of the ground surface was simulated. The numerical results show that compared with the rectangular open trench, the part of the area behind the new cross section trench has better isolation efficiency, Cross section 6 seems to be the most efficient of the six cross sections, and the isolation efficiency is improved by nearly 10.2% compared. Increasing the cross-sectional area could not effectively improve the isolation efficiency of the open trenches. Selection of inclination of the hypotenuse to an appropriate angle, increasing the number and depth of open trenches could improve the isolation efficiency. The vibration isolation performance of the trenches in the soft soil was better than the stiff soil. Besides, an excessively high groundwater table is usually detrimental to the isolation efficiency of the trenches.

Analyzing the stability of slopes during rainfall can be critical in preventing landslide disasters. In this study, on the basis of the limit analysis method, a novel method for computing the safety factor of slopes considering transient unsaturated seepage effect is proposed, which considers the hydromechanical coupling effect. The proposed method is appropriate for vertical cut slopes which cannot be solved by the infinite slope analysis method. Two cases validate the proposed method. In the proposed method, the safety factor of slopes can be obtained by a simple optimization algorithm. The number of the independent variables of the proposed method is usually less than that of the limit-equilibrium method. The effect of hydrological parameters (the ratio of rainfall intensity to saturated permeability coefficient, desaturation coefficient, elasticity modulus related to suction), slope geometric parameters (slope angle and slope height), and soil shear strength parameters (effective cohesion and effective internal friction angle) on safety factor is also studied. The results show that the hydromechanical coupling has a great impact on slope stability, and the effect of shear strength parameters on slope stability is greater than that of geometric parameters. The hydrological parameters mainly control the degradation degree of slope safety factor over time. For actual slopes that do not completely satisfy the assumption of infinite slopes, too conservative results may be obtained by the infinite slope analysis method, resulting in huge economic waste in engineering construction.

Due to urbanization, development of society, and growth of population, there are new demands for tunneling technique to facilitate the public transport as well as high-rise buildings to accommodate an increasing population. Piled foundations are commonly preferred for the construction of high-rise buildings. It is, therefore, unavoidable that tunnels must be constructed near extant buildings resting on piled foundations. Inevitable movement of the ground due to stress changes induced by a tunnel can induce additional settlement and reduce the load-carrying capacity of nearby pile foundation systems. This numerical parametric study investigates the responses of two-by-two piled raft to twin side-by-side tunnels either near the mid-depth of the pile shaft or adjacent to or below the pile toe in stiff clay. In addition, it investigates the effects of different group configurations of the piled raft and elevated pile group. The ground in all the finite-element analyses was modeled using the hypoplasticity (clay) model because of its ability to capture degradation of soil stiffness at a small-strain level. Twin tunneling below the pile and near the middepth of the pile shaft caused the largest and smallest settlement of the piled raft, respectively. Unlike induced piled raft settlement, the most significant transverse tilting of the raft is induced after the advancement of the first tunnel. After the twin tunneling near the pile shaft was completed, the raft was separated from the ground, and a portion of the working load carried by the raft was transferred to the piles. The computed results have revealed that the induced settlement of the elevated pile group was significantly larger than that of the piled raft. A significant effect number of piles in the group was found on the piled raft responses to tunneling.

This paper presents a new method for the nonlinear analysis of rafts resting on multilayered heterogeneous soils using the Vlasov model. The finite-element and the finite-difference methods are employed to solve the governing differential equations for the flexure of the raft and the displacement within the supporting soil mass, respectively. The soil heterogeneity in the vertical direction or in the horizontal directions within each soil layer is considered, and the soil nonlinearity is taken into account through the reduction of the soil shear modulus as a function of strains within the supporting soil mass. Through a comprehensive comparative study, it is found that the present method is validated as reasonable by field measurements and is in good agreement with nonlinear three-dimensional finite-element analysis and other existing analysis methods. A study is carried out to investigate the effect of soil layering, soil nonlinearity, and soil heterogeneity in the vertical direction and in horizontal directions on the raft behavior. It is concluded that neglecting the real conditions of the supporting soils (e.g., soil layering, soil nonlinearity, and soil heterogeneities in the vertical or in horizontal directions) in the analysis of the soil–raft interaction leads to an unrealistic prediction of the raft behavior.

Semianalytical or analytical models for calculating active and passive earth pressure coefficients for undrained soil–wall systems subjected to head rotation are rare. To fill this gap, this study proposes a semianalytical theoretical model that describes the real failure features of wall–soil systems with head rotation and under undrained conditions. A continuous velocity field (CVF) that is decomposed into circular and radial velocity components is generated to characterize the movement of undrained soils in the plastic zone. The closed-form solutions of active and passive earth pressure coefficients are formulated based on the upper-bound limit analysis (UBLA) theorem. A comparison with numerical simulations and Rankine’s theory are performed to illustrate the importance of wall movement and the contributions of undrained cohesion. The analysis outcomes demonstrate that (1) the conventional stress-based method that ignores the head rotation of walls leads to an error of earth pressure coefficients up to 15.7%; and (2) the active and passive earth pressure coefficients have linear relationships with undrained cohesion. Finally, an application to shallow excavation is conducted, showing the good performance of the proposed model.

Approach slabs are commonly used to smooth the transition between an integral bridge abutment and its adjacent backfill-supported pavement where differential settlement may exist. This settlement can be aggravated by abutment cyclic movements caused by seasonal temperature changes. When the backfill surface settlement near the abutment is large enough to create a void under the approach slab, traffic loads on the approach slab are transferred to the abutment and the end of the approach slab near the adjacent pavement. Differential settlement may also develop at the joint between the approach slab and the adjacent pavement due to traffic loading. Sleeper slabs on geosynthetic-reinforced soil have been proposed to be placed underneath the joint to mitigate this differential settlement. However, no physical model test has been conducted so far to investigate the effects of traffic loading on the approach slab and the mitigation benefits of geosynthetic reinforcement under the sleeper slab. In this study, three physical tests were designed and conducted to fill this knowledge gap. This study found that compaction of the backfill by contact stresses under the approach slab and movements of the abutment due to traffic loading caused backfill surface settlement. As the backfill surface settlement increased, the contact stresses under the approach slab and the sleeper slab decreased. Geosynthetic reinforcements under the sleeper slab reduced the contact stresses under the approach slab, thus minimizing the settlement, but increased the contact stresses under the sleeper slab. In addition, the geosynthetic reinforcements significantly reduced the differential settlement between the two sides of the sleeper slab.

Rock heterogeneity is one of the most important factors when numerically simulating the rock failure process and crack propagation. This paper presents an approach for capturing rock heterogeneity that combines peridynamic theory, digital image processing (DIP), and low-field nuclear magnetic resonance (NMR) imaging. By processing the magnetic resonance images (MRIs) of the rock material, the microstructure distribution is obtained, and the attenuation coefficient is defined and calculated by the number and value of pixels of the rock MRI. Based on bond-based peridynamic theory, the density, bond constant, and critical stretch associated with the material point and bond are revised by the attenuation coefficient and have the same distribution with real rock microstructure. Then, this new approach is used to simulate the crack bifurcation of red sandstone under tension and the failure process of mudstone in an unconfined compression test. The influence of the element’s pixel number on the calculation result is discussed. Numerical results show that the crack propagation and the failure process based on the new approach are both distributed nonsymmetrically. In addition, the acoustic emission rule in the peridynamic simulation, which is defined by the number of broken bonds in each loading step, is consistent with the experimental results. The comparison of the numerical and experimental results reveals that the present approach can be used as a supplementary method for analyzing rock damage and failure.

Finite element analyses are performed to investigate the influence of layered clays on the undrained response of embedded strip footings under uniaxial and combined loading. A fully bonded footing–soil interface was considered to comply with the undrained condition. Transformation in failure mechanism under uniaxial (vertical, horizontal, and moment) loading due to the involvement of the soft/strong underlying clay is extensively studied. Analysis-based bearing capacity values of strip footing for different combinations of embedment, top layer depth, and shear strength ratio are provided. The present study accounts for the interaction between coupling of horizontal and rotational displacements and underlying clay layer properties while investigating the combined load response. Subsequent effect of this interaction on the maximum and ultimate horizontal and moment capacities are quantified. In addition, the contribution of different footing and soil properties in altering size and obliquity of the failure envelope is categorically studied.

Concrete piles are used conventionally to reinforce slurry trench against global collapse during excavation in surrounding soft soil layers. In this paper, the stabilizing forces acting on piles were analyzed with the framework of the upper-bound approach of limit analysis combined with a rotational failure mechanism in undrained soil conditions. A trench without pile reinforcement was considered first, and the results obtained in the proposed approach agreed well with those obtained through the limit-equilibrium and variational limit-equilibrium closed-form solutions. It was shown that the trench has a deeper critical excavation depth as the stabilizing force provided by piles becomes greater. In addition, the critical sliding surface tended to be shallower with a decrease in the ground surcharge coupled with a surcharge near the edge of the trench. Finally, the required stabilizing forces were needed to increase rapidly to enhance the safety factor of the trench to 1.0. However, due to the reinforcement of slurry pressure and soil self-stabilization, the stabilizing forces were not always required at all excavation depths; only when excavation exceeds a certain depth could the reinforcing effect of piles be exerted.