Numerical simulation on the mechanical and fracture behavior of bedding argillaceous sandstone containing two pre-existing flaws

Abstract

The overlying strata will move and generate flaws as the coal mining workings advance, and the development of flaws can affect the collapse process of the overlying strata, studying the fracture behavior under different pre-existing flaws conditions is crucial to maintain the stability of coal mining workings. In this work, a series of bedding argillaceous sandstone models containing two pre-existing flaws (i.e. bottom flaw length, included angle between upper and bottom flaw, and loading rate) were simulated under uniaxial compression experiments based on the discrete element method (DEM) under the moment tensor theory. The research results show that the increasing in included angle and loading rate lead to an increase in peak strength and a decrease in the angle of the main fracture plane. The variation of peak strength and b-value decreases with the bottom flaw length, with smaller tensile acoustic emission (AE) event and larger shear AE event for interlayer and bedding cracking, respectively. The crack-in-matrix presents a concave tendency with bedding angle, leading to a failure pattern change from matrix-dominated, matrix-bedding to bedding-dominated in a lower b-value. Loading rate promotes the change of AE event from tensile to shear mode with a wider fracture plane. In terms of brittleness, the range of brittleness is mainly between moderate brittleness and brittleness, and decreases and increases as the bottom flaw length and the included angle, respectively, exhibit a linear correlation in strength, independent of the loading rate to models. The research results could contribute to the comprehension of cracking mechanisms and improve safe production at coal mine workings of bedding strata.