Journal of Rock Mechanics and Geotechnical Engineering最新文献

Low-frequency vibrations can effectively improve natural sandstone permeability, and higher vibration frequency is associated with larger permeability. However, the optimum permeability and permeability evolution mechanism for uranium leaching and the relationship between permeability and the change of chemical reactive rate affecting uranium leaching have not been determined. To solve the above problems, in this study, identical homogeneous sandstone samples were selected to simulate low-permeability sandstone; a permeability evolution model considering the combined action of vibration stress, pore water pressure, water flow impact force, and chemical erosion was established; and vibration leaching experiments were performed to test the model accuracy. Both the permeability and chemical reactions were found to simultaneously restrict U⁶⁺ leaching, and the vibration treatment increased the permeability, causing the U⁶⁺ leaching reaction to no longer be diffusion-constrained but to be primarily controlled by the reaction rate. Changes of the model calculation parameters were further analyzed to determine the permeability evolution mechanism under the influence of vibration and chemical erosion, to prove the correctness of the mechanism according to the experimental results, and to develop a new method for determining the optimum permeability in uranium leaching. The uranium leaching was found to primarily follow a process consisting of (1) a permeability control stage, (2) achieving the optimum permeability, (3) a chemical reactive rate control stage, and (4) a channel flow stage. The resolution of these problems is of great significance for facilitating the application and promotion of low-frequency vibration in the CO₂ + O₂ leaching process.

Displacement-monitoring-based back analysis is a popular method for geomechanical parameter estimation. However, due to the delayed installation of multi-point extensometers, the monitoring curve is only a part of the overall one, leading to displacement loss. Besides, the monitoring and construction time on the monitoring curve is difficult to determine. In the literature, the final displacement was selected for the back analysis, which could induce unreliable results. In this paper, a displacement-based back analysis method to mitigate the influence of displacement loss is developed. A robust hybrid optimization algorithm is proposed as a substitute for time-consuming numerical simulation. It integrates the strengths of the nonlinear mapping and prediction capability of the support vector machine (SVM) algorithm, the global searching and optimization characteristics of the optimized particle swarm optimization (OPSO) algorithm, and the nonlinear numerical simulation capability of ABAQUS. To avoid being trapped in the local optimum and to improve the efficiency of optimization, the standard PSO algorithm is improved and is compared with other three algorithms (genetic algorithm (GA), simulated annealing (SA), and standard PSO). The results indicate the superiority of OPSO algorithm. Finally, the hybrid optimization algorithm is applied to an engineering project. The back-analyzed parameters are submitted to numerical analysis, and comparison between the calculated and monitoring displacement curve shows that this hybrid algorithm can offer a reasonable reference for geomechanical parameters estimation.

One of the major factors inhibiting the construction of deep underground projects is the risk posed by rockbursts. A study was conducted on the access tunnel of the Shuangjiangkou hydropower station to determine the evolutionary mechanism of microfractures within the surrounding rock mass during rockburst development and develop a rockburst warning model. The study area was chosen through the combination of field studies with an analysis of the spatial and temporal distribution of microseismic (MS) events. The moment tensor inversion method was adopted to study rockburst mechanism, and a dynamic Bayesian network (DBN) was applied to investigating the sensitivity of MS source parameters for rockburst warnings. A MS multivariable rockburst warning model was proposed and validated using two case studies. The results indicate that fractures in the surrounding rock mass during the development of strain-structure rockbursts initially show shear failure and are then followed by tensile failure. The effectiveness of the DBN-based rockburst warning model was demonstrated using self-validation and K-fold cross-validation. Moment magnitude and source radius are the most sensitive factors based on an investigation of the influence on the parent and child nodes in the model, which can serve as important standards for rockburst warnings. The proposed rockburst warning model was found to be effective when applied to two actual projects.

Through high-precision engraving, self-affine sandstone joint surfaces with various joint roughness coefficients (JRC = 3.21–12.16) were replicated and the shear sliding tests under unloading normal stress were conducted regarding various initial normal stresses (1–7 MPa) and numbers of shearing cycles (1–5). The peak shear stress of fractures decreased with shear cycles due to progressively smooth surface morphologies, while increased with both JRC and initial normal stress and could be verified using the nonlinear Barton-Bandis failure criterion. The joint friction angle of fractures exponentially increased by 62.22%–64.87% with JRC while decreased by 22.1%–24.85% with shearing cycles. After unloading normal stress, the sliding initiation time of fractures increased with both JRC and initial normal stress due to more tortuous fracture morphologies and enhanced shearing resistance capacity. The surface resistance index (SRI) of fractures decreased by 4.35%–32.02% with increasing shearing cycles due to a more significant reduction of sliding initiation shear stress than that for sliding initiation normal stress, but increased by a factor of 0.41–1.64 with JRC. After sliding initiation, the shear displacement of fractures showed an increase in power function. By defining a sliding rate threshold of 5 × 10⁻⁵ m/s, transition from “quasi-static” to “dynamic” sliding of fractures was identified, and the increase of sliding acceleration steepened with JRC while slowed down with shearing cycles. The normal displacement experienced a slight increase before shear sliding due to deformation recovery as the unloading stress was unloaded, and then enhanced shear dilation after sliding initiation due to climbing effects of surface asperities. Dilation was positively related to the shear sliding velocity of fractures. Wear characteristics of the fracture surfaces after shearing failure were evaluated using binary calculation, indicating an increasing shear area ratio by 45.24%–91.02% with normal stress.

Despite the extensive studies conducted on the effectiveness of microwave treatment as a novel rock pre-conditioning method, there is yet to find reliable data on the rock failure mechanisms due to microwave heating. In addition, there is no significant discussion on the energy efficiency of the method as one of the important factors among the mining and geotechnical engineers in the industry. This study presents a novel experimental method to evaluate two main rock failure mechanisms due to microwave treatment without applying any mechanical forces, i.e. distributed and concentrated heating. The result shows that the existence of a small and concentrated fraction of a strong microwave absorbing mineral will change the failure mechanism from the distributed heating to the concentrated heating, which can increase the weakening over microwave efficiency (WOME) by more than 10 folds. This observation is further investigated using the developed coupled numerical model. It is shown that at the same input energy, the existence of microwave absorbing minerals can cause major heat concentration inside the rock and increase the maximum temperature by up to three times.