Spalling failure and fracturing of brittle sandstone containing rectangular cavity based on biaxial compression test and discrete element method

Excavation of tunnel in hard brittle rock commonly induces disasters like spalling failure and rock burst, and numerous relevant theoretical, experimental and numerical studies are finished to detect the specific destruction mechanism. However, only a small number of researches focused on the excavation of underground mining stope, and the largest feature is the rectangular cavity and the gradient height of the cavity. Therefore, to mimic the failure procedure of the surrounding rock of the mining stope, six groups of rock samples containing various cavity heights are applied in the biaxial compression test (two types of confining pressures), and the PFC method is utilized to explain the failure mechanism in microscopic scale. The main results and conclusions are as follows: (1) The confining pressure directly affects the time relationship between the visible spalling failure and the typical AE burst incident. (2) As the cavity height increases, the spalling failure cannot cover the whole sidewall at once and transforms into localized destruction, which advances the corresponding initial appearance time. (3) The striped tensile failures distribute in the roof and bottom surrounding rock of rectangular cavity; tensile failures cover the whole spalling regions in sidewalls, while the shear failures are mainly concentrated in the lower part of the spalling areas. (4) When the cavity height is relatively large, the spalling failure in both sidewalls exhibits asymmetric distribution during the majority period of the test, and the final failure surface only shows an approximate symmetrical distribution.