Experimental Study on Failure Mode and Fracture Evolution Characteristics of Red Shale in Kaiyang Phosphorus Mining Area

Abstract In order to study the failure mode and fracture evolution characteristics of red shale in Kaiyang Phosphorus mining area, conventional triaxial compression mechanical tests of red shale with different bedding dip angles were carried out by using DSTD-1000 electro-hydraulic servo rock mechanics experiment system. Based on the laboratory test results, the conventional triaxial particle flow simulation of red shale samples with different bedding dip angles was carried out using discrete element PFC2D. The results show that: (1) the failure mode of red shale is controlled by bedrock when the bedding dip angle is 0° and 60°~ 90°. When the bedding dip angle is 15°~ 45°, the rock failure mode is controlled by bedding. The compressive strength of rock is the minimum when the bedding dip angle is 30°and the maximum at 0°, which is about 2 times of the minimum. (2)In the failure process of red shale, the cracks with different bedding dip angles show slow growth stage, accelerated growth stage and stable stage with axial strain. The whole failure process is dominated by tensile cracks, accompanied by a few shear cracks. (3)The type of displacement field varies with the bedding dip angle: tensile failure and shear failure are the main displacement field types at 15°~ 45°, and mixed failure is often the main mode at 60°~ 90°and 0°. The research results provide the basis and reference for the safety control of red shale roadway.