International Journal of Geomechanics

The current analytical solutions for axisymmetric active earth pressure are based on certain hypothetical relationships between the circumferential stress, the average stress of the meridional plane, and the main shear stress of the meridional plane. To get a stricter analytical solution, the strict mathematical relationship between them is derived based on the circumferential geometric condition, plastic flow theory, and plastic potential theory in this study. A new axisymmetric characteristics theory, which takes into account the friction angle, the dilatation angle of the soil, and the flow velocity, is established. A new analytical solution for axisymmetric active earth pressure is derived based on the new axisymmetric characteristics theory and the hypothesis of the active static state. The solutions developed in this study and the active static-state hypothesis are demonstrated to be reasonably accurate compared with a set of experimental data obtained from the literature. Various comparative analyses were conducted, and many interesting conclusions are obtained; it is found that the analytical solution is greater than the numerical solution. The analytical and numerical solutions for pressure caused by surcharge and weight fall between the solutions of Berezantzev ($\lambda =1$) and Cheng ($\lambda =K_O$), whereas the analytical and numerical solutions for pressure caused by cohesion are greater than those of Berezantzev and Cheng.

Seasonal conditions (e.g., rise in the water table, precipitation, freeze–thaw cycles, and wet–dry cycles) affect stabilized subgrade moisture conditions which, in turn, have a significant impact on in-service pavement performance. Studies have shown the effect of seasonal conditions on stabilized subgrade soils’ mechanical properties, including unconfined compression strength (UCS), modulus of elasticity (E), and resilient modulus (M_R). There have been a limited number of studies addressing the hysteretic behavior of UCS, E, and M_R in stabilized subgrade soils with moisture conditions. This study investigated the impact of moisture hysteresis on the UCS, E, and M_R values of stabilized fine-grained soils following wetting, drying, and wetting–drying cycles. The results of this study can help predict changes in the bearing capacity of pavements subjected to seasonal conditions. Cylindrical specimens were first prepared with optimum moisture content and maximum dry unit weight. After each specimen’s moisture content was altered to attain the target moisture content, the specimens were tested for UCS, E, and M_R values. The tests showed hysteretic behavior comparable to the soil–water characteristic curve; specimens subjected to wetting had lower M_R values than those subjected to drying. The hysteretic behavior of the mechanical properties in stabilized specimens can be explained by the following: (1) wetting and drying accelerates chemical reactions, (2) soil suction changes within the pores, and (3) hydration and Born repulsion create repelling/attracting. Scanning electron microscope (SEM) micrographs show increased cementation products within specimens subject to drying and wetting–drying cycles. Findings also showed that pavement distresses, namely rutting and AC bottom-up fatigue cracking, changed as moisture content varied. However, the impact of moisture variations was more evident in a thin-HMA pavement section compared to a thick-HMA pavement section.

The disturbed state concept (DSC) is widely used to capture the cracking, breaking, heating, softening, and hardening behaviors of geomaterials. In this study, a constitutive model for overconsolidated clays is proposed by incorporating the DSC. A new disturbance function describes the effect of the overconsolidation ratio (OCR) on the strength, dilatancy, and deformation of overconsolidated clays. This disturbance function is incorporated into the potential-failure and dilatancy stress ratios, potential-failure and dilatancy lines, and potential-failure and dilatancy surfaces at the current and referenced states. The plastic moduli also pertain to this disturbance function. With the assistance of this disturbance function, the proposed model can capture the strain hardening and volumetric contraction of normally consolidated or slightly overconsolidated clays, as well as the strain softening and volumetric expansion of highly overconsolidated clays under the drained condition. It can also capture the evolution of strength, excess pore pressure, and stress paths under the undrained condition.

The disturbed state concept (DSC)-based model for overconsolidated clay was proposed mainly in a previous paper that aims to analyze the influences of the model parameters on model predictions, calibrations of the model parameters, and the model validation through different overconsolidated clays. It is found that the disturbance parameter in the model predictions can greatly influence the evolution of stress, volumetric strain, undrained shear strength, and excess pore pressure with axial strain. Detailed calibrations of the model parameters, such as the disturbance parameter, potential-failure and dilatancy parameters, and plastic modulus parameters, are introduced. The comparison results demonstrate that the DSC-based model predictions are in good agreement with the test data of different overconsolidated clays on strain softening and volumetric expansion under the drained condition, as well as the evolution of undrained shear strength and excess pore pressure during the undrained shearing process.

Loess, a kind of special soil, is widespread in the seasonally frozen soil regions and featured with well-developed joints and pore structure. Notwithstanding, the permeability anisotropy nature of loess can badly impact the safety of construction in such regions. Despite many influencing factors, the effect of dry density and freeze–thaw cycles plays a major role in the permeability anisotropy nature. This study uses the Global Digital Systems (GDS) triaxial permeability apparatus to investigate the permeability anisotropy nature of the Q₃ horizontally and vertically cut loess specimens retrieved from an excavation pit in Xi’an, Shaanxi Province. The experimental results show that the loess possesses a distinct permeability anisotropy nature, and it is intensified when subjected to the effect of particle densification. The higher the initial moisture content, the greater the pore structure change, and the weaker the permeability anisotropy nature. The increasing cycle number promotes the growth of pore ice and subsequently the bridging pore structure, improving the pore connectivity. Despite the bridging impeding the groundwater seepage in the vertical direction, the freezing–thawing cycle of more than five times, in turn, mitigates this phenomenon, and the pore connectivity in the vertical direction outweighs the horizontal one in the end.

In practice, slopes with cracks are very common, particularly in earthquake-prone areas. The slope soil properties exhibit spatial nonhomogeneity because of the geological and environmental effects. This article investigates the stability of nonhomogeneous slopes with cracks under seismic loading. The failure mechanism of nonhomogeneous slopes with cracks is first proposed using the discretization technique. Cracks are considered to be formed as a part of the failure mechanism. The pseudodynamic approach is then adopted to analyze the influence of seismic forces. The present discretization mechanism is validated by comparisons with existing studies. Discussions are also carried out to (1) identify the differences between the pseudostatic and pseudodynamic approaches, (2) assess the effects of the seismic forces and existence of cracks on slope stability, and (3) analyze the influence of earthquake parameters and soil nonhomogeneity. The pseudodynamic approach can consider the time and space variation of the ground shaking in the seismic analysis, which is more realistic. The results obtained by the pseudodynamic approach were found to differ a lot compared with that of the pseudostatic approach for higher values of $k_h$ and amplification factor $f$. For steeper slopes, considering the presence of cracks also has a great influence on the safety factor with an increase in $k_h$.

The swell-collapse mechanism of residual basaltic clay in both untreated and stabilized with lime conditions was investigated. For treated specimens, the optimum lime content (OLC) was found based on swell potential reduction. Swelling and collapse potential were investigated using the virgin compaction surface, which is the backbone of the Monash-Peradeniya-Kodikara (MPK) framework. The suitability of the MPK was examined by applying different state paths. The swelling and collapse potentials were tested under a wide range of moisture contents and stress levels, with attention given to the effect of stress history and operational stress. Test results indicated that for the untreated and lime-treated clay (at OLC), the behavior of soil during loading, unloading, and wetting closely followed the MPK framework. However, the MPK did not extend to specimens with very low moisture content wetted under low stresses, and, consequently, a new improved model was suggested. Furthermore, a new method for predicting the swelling and collapse potential was proposed using the virgin compaction surface.

Seismic slope stability analysis is often limited by the ability to encompass specific earthquake characteristics, such as shaking amplitude, frequency, and time as well as varying soil properties, such as cohesion and friction angle across the depth with consideration of damping and amplification. In this paper, a simple procedure that combines the discretization-based kinematic analysis and modified pseudodynamic method is presented to offer a more holistic analysis considering earthquake and soil characteristics more appropriately. This is achieved by the implementation of the discretization-based kinematic analysis along with a modified pseudodynamic method. The discretization technique aids to generate a kinematically admissible failure surface with considerations to varied soil strength parameters. Its significance lies in the preprocessing to generate a unique failure mechanism dependent on the varied soil properties of the slope while also facilitating the work rate calculations. The use of the modified pseudodynamic method is adopted in this study to overcome the shortcomings of the pseudostatic and simple pseudodynamic method, enabling one to consider the complete time history of earthquake-induced ground movement, having also considered the amplification effect when shaking approaches the soil’s natural frequency. Equating the external and internal rates of work by integration of elementary rates yields the closed-form solution in yield seismic acceleration and/or slope-bearing capacity. A parametric study with a range of independent variables, accompanied with detailed discussion, is also presented to offer a more pragmatic perspective on the performance of nonuniform stratified slopes subjected to earthquakes.

The vertical load acting on a support structure is affected by the loss of self-bearing capacity of the rock inside the plastic zone. This load can then be accounted for by analytical calculation methods capable of evaluating the stresses in the tunnel support system to proceed with the tunnel design. Generally, the effect of the rock’s own weight in the plastic zone is considered in a simplistic way by evaluating an additional vertical load given by the weight of the rock due to the thickness of the plastic zone. This approach leads to a significant increase in the vertical load with the risk of overdesigning the support structure. In this work, the effect of the rock’s own weight in the plastic zone was considered by modifying the numerical solution of the convergence-confinement method for tunnels built in rock. In this way, through the intersection of the characteristic curve of the tunnel and the intersection line of the support structure, it is possible to determine both the vertical loads (with the effect of the weight of the rock) and the horizontal load (without the effect of weight of the rock). The application of the method to a project in the Alps allowed the detection of the magnitude of the percentage increase of the vertical load and a significant increase in the thickness of the plastic zone and determination of the consequences that this may have on the designing of the radial bolting length in that zone. Increasing the plastic radius led to an increase in the length of the bolts. This is interesting because, in the area of the crown where the weight of the plasticized rock is considered, the bolts are usually installed with a greater length. In the final part of the study, a new procedure was illustrated to define the vertical and horizontal loads acting on the support structures, starting from the convergence-confinement curves obtained for the crown and for the lateral areas (sides).