Research on Macro-Micro Failure Mechanism of Interbedded Sandstone in the Deep of Lannigou Gold Mine

The surrounding rock of the Lannigou gold mine roadway is mainly sandstone, most of which contains thin interlayers of argillaceous and carbonaceous minerals. To explore the deformation and failure mechanism of interbedded sandstones under static load caused by surrounding rock stress, the macroscopic failure modes, macroscopic physical properties, and microscopic fracture surface characteristics of sandstones were studied from different inclination angles. Triaxial compression tests and scanning electron microscopy tests were conducted. The results show that the peak strength of the specimen changes in a “spoon”-shaped pattern with increasing inclination. With increasing confining pressure, the peak strength, peak strain, residual strength, and elastic modulus of specimens increase, which damages interlayers. The macroscopic failure mode is mainly affected by the interlayer without confining pressure, and both tensile-shear failure (0° and 90°) and composite failure (30° and 60°) occur. Under higher confining pressure, the effect of the interlayer is smaller, and the specimen shows shear-tensile failure (0°, 30°, 60°, and 90°). Furthermore, the propagation mode of microcracks and the microscopic failure mode of mineral crystals differ for different macroscopic failure modes. In this study, the microscopic mechanism of macroscopic failure of interbedded sandstone was identified, which is significant for practical engineering guidance.