Red shale is widely distributed among the deep mine areas of Kaiyang Phosphate Mine, which is the biggest underground phosphate mine of China. Because of the effect of various factors, such as high stress, ground water and so on, trackless transport roadways in deep mine areas were difficult to effectively support for a long time by using traditional supporting design methods. To deal with this problem, some innovative works were carried out in this paper. First, mineral composition and microstructure, anisotropic, hydraulic mechanical properties and other mechanical parameters of red shale were tested in a laboratory to reveal its deformation and failure characteristics from the aspect of lithology. Then, some numerical simulation about the failure process of the roadways in layered red shale strata was implemented to investigate the change regulation of stress and strain in the surrounding rock, according to the real rock mechanical parameters and in-situ stress data. Therefore, based on the composite failure law and existing support problems of red shale roadways, some effective methods and techniques were adopted, especially a kind of new wave-type bolt that was used to relieve rock expansion and plastic energy to prevent concentration of stress and excess deformation. The field experiment shows the superiorities in new techniques have been verified and successfully applied to safeguard roadway stability.
In this study, a measurement system for gas generation of coal-rock under temperature–pressure coupling was developed by adding gas extraction, collection, and flow-monitoring devices to the original stainless-steel liquid seepage pipeline of an MTS-815 rock triaxial testing machine, which can be used to study the production mechanism of coalbed methane in a real geological environment. The system has the functions of axial loading, confining pressure loading, continuous heating, gas gathering, etc., and has the advantages of good air tightness, high accuracy and stability, long-term loading and heating, and controllable single variables. The preliminary test for the gas production of anthracite in the Shaanxi Formation of the Qinshui Basin under temperature–pressure coupling was carried out by the developed test system. The results show that the test system can provide accurate and effective measurement means for the study of gas production by coal-rock deformation and is expected to provide effective help for the control and exploitation of coalbed methane.
To study the mechanical properties and failure modes of the Brazilian disc under biaxial splitting loading, different stress ratios (i) (axial stress:lateral stress) i = 1:1, 2:1, 3:1, 4:1, and ∞:1 are experimentally applied in sandstone discs by a hydraulic servo-controlled testing machine equipped with a lateral loading device. Meanwhile, digital image correlation (DIC) and the FLAC3D are used to obtain the strain field and stress field evolution of the specimens. It was found that the presence of lateral pressure limits, the formation of horizontal tensile stress to varying degrees, and the axial peak loads decrease with the stress ratio. The failure modes that the rock discs underwent were shear failure, shear-tension mixed failure, and tensile failure as the stress ratio increased. The DIC results show that the maximum strain field gradually transitioned from the adjacent loading points of the discs to between two loading points in the axial direction with the stress ratio. In addition, the simulation results also demonstrated the transformation of the dominant stress in the stress field from tensile stress to shear stress with increasing lateral pressure.
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