Abstracts:A nonlinear consolidation model of soils with vertical drains was developed by combining the fact that well resistance varies linearly with depth and exponentially with time. In addition, three variation modes related to horizontal permeability in the smear zone were used to improve this model. The degree of consolidation, excess pore pressure, and settlement of soil layers under multistage loading were simulated by the finite-difference method. The proposed solution was verified through a comparison with the literature to demonstrate its validity. Ultimately, the effects of various parameters associated with well resistance, the ratio of compression index to permeability index, external loading, smear effects, and the distribution of initial average effective stress along the depth on consolidation behaviors were investigated in this study.

Abstracts:The changes in mechanical behaviors of soils after cyclic loading will lead to the generation of additional settlements. The postcyclic stiffness characteristics of soils are usually analyzed by using conventional cyclic triaxial tests, in which only cyclic deviator stress is applied under undrained conditions; however, the cyclic variations of both axial stress and horizontal stress under traffic loading were observed. Moreover, the pore water was permitted to drain under cyclic loading. Therefore, cyclic triaxial tests under partially drained conditions were performed to investigate the postcyclic stiffness characteristics of remolded laterite clay. The influences of variables, such as the cyclic deviator stress, number of cycles, cyclic confining pressure, and degree of reconsolidation, were evaluated. The postcyclic elastic modulus increases as the cyclic deviator stress, number of cycles, and degree of reconsolidation increase, while it decreases as the cyclic confining pressure increases. Nevertheless, the ratio of the postcyclic elastic modulus with and without cyclic confining pressure decreases as the cyclic confining pressure increases; the postcyclic elastic modulus ratio of the degree of reconsolidation to without reconsolidation increases linearly with the increasing degree of reconsolidation. Based on the result, an empirical formula for the postcyclic elastic modulus, considering the effects of both cyclic confining pressure and the degree of reconsolidation, was proposed. The predicted results match the measured data well, indicating that the formula is valid for the prediction of the postcyclic elastic modulus of laterite clays after cyclic loading.

Abstracts:Understanding gas migration behavior in host rocks is of importance to the safety evaluation of deep geological repositories for nuclear waste. Experimental results reported in the literature show that gas flow in saturated claystone is through a highly localized network of dilatant pathways and that water is barely displaced. To explain the specific gas migration behavior, a two-scale approach is developed. A subcritical criterion for microcrack propagation is proposed to represent the time-dependent damage at the macroscale. The passage from microscale to macroscale is implemented through an asymptotic homogenization method. The solid mechanics is coupled with the fluid flow through pore pressure variation and an intrinsic permeability model, which implicitly accounts for the fracture opening induced permeability change. The developed model is tested against both laboratory and in situ gas injection experiments in the literature. Some key experimental findings, such as the development of preferential gas pathways and the fully saturated state are explicitly captured by the poroelastic damage model. Model results explain that the highly localized fracture pathways are the major places where gas and water interact with each other, and as a result the whole rock is almost kept fully saturated, which helps us get in-depth understanding of this gas transport mechanism.

Abstracts:Achieving slope stabilization by placing anti-slide piles has become an effective slope-reinforcement technique in geotechnical engineering. Based on the limit analysis method, this study investigated the 3D stability of unsaturated inhomogeneous piled slopes, incorporating three failure patterns: toe-failure, face-failure, and base-failure. The suction and effective unit weight profile under different effective saturation were considered and the soil cohesion was assumed as varied linearly with depth. A theoretical analysis of the lateral force acting on a row of rigid anti-slide piles with the same spacing in a row through plastically deforming soils is described while considering the soil suction and inhomogeneity. In addition, a new formula was developed to calculate the lateral forces provided by a row of piles. The genetic algorithm (GA) was used to obtain the minimum value of the factor of safety F_S and the corresponding critical slip surface. The results of the study were compared with those of the existing literature to verify the feasibility of the proposed approach. In addition, the influences of key parameters on F_S of 3D piled slopes were investigated by parametric analysis. The numerical results indicate that piled slope stability will be underestimated when the 3D effects and suction are not considered, and soil inhomogeneity has a negative impact on piled slope stability. It was also found that the probability for the occurrence of face-failure increases with increasing inhomogeneity and decreasing suction-induced effect, and the occurrence of face-failure significantly reduces the pile reinforcement effect. In addition, when the anti-piles are located at the slope toe, the base-failure mechanism yields the critical values of F_S in most cases. This study can provide several reasonable suggestions for engineering applications and a theoretical basis for further studies on the stability of slopes reinforced with piles.

Abstracts:Hot dry rock (HDR) geothermal energy is clean energy that can meet people’s demand for low carbon. The traditional hydraulic fracturing method is challenging to break HDR dominated by granite, mainly because of HDR’s high temperature and hard characteristics. Microwave irradiation is considered a proven approach to breaking granite. This study investigates the failure mechanism of HDR at 500°C–800°C under microwave irradiation. The experiments cover preheating, uniaxial compression, granulometric analysis, binocular vision monitoring (BVM) technique, and X-ray powder diffraction. The result shows that the uniaxial compression strength of granite decreases the most at 500°C–600°C, which is 62.77% on average. The failure form is from the brittle failure (untreated) to ductile failure (800 °C) with the rise of the microwave irradiation temperature. The microwave makes a particle size in the range of 0.6–2.36 mm the most apparent particle size of granite after uniaxial compression. The BVM technique reconstructs the surface deformation with a 0.7% error. Microwaves cause heat accumulation near the rock near the magnetron, resulting in the formation of crack networks and a molten cavity. The possibility of microwave-assisted fracturing of HDR is discussed at the end of the article.

Abstracts:Thermal operations threaten the safety of geological engineering, especially the rock–concrete interface, as the link of in situ stress transmission is crucial to structural stability. In this study, three-point bending experiments were conducted on sandstone–concrete binary specimens to investigate the thermal effect on fracture behaviors of the rock–concrete bonding interface. The deformation evolution characteristics were analyzed by digital image correlation (DIC). The results demonstrated that the temperature has a remarkable degradation for the bonding capacity of sandstone–concrete interfaces, which can be classified into the rapid-damage stage and steady-damage stage with a critical temperature of 300°C. The phased degradation is closely related to the decline in interfacial adhesion and the thermal damage to concrete, instead of sandstone. By determining the strain inflection point of different positions on the crack path, a new idea is proposed to reveal the crack propagation process. During the loading process, the crack propagates slowly to a certain length and then coalescences violently when subjected to a small load increment. In addition, the crack initiation load is weakened by the elevated temperature or lower interface roughness.