Numerical simulation of blasting-induced fracture expansion in coal masses

Abstract

Bedding planes are common in coal seams, and have a significant influence on the crack expansion of coal masses. In this paper, the fracture patterns of coal masses during the blasting process are explored. Firstly, the damage zone at the tip of beddings is calculated based on the Kachanov equation, and crack connections among bedding planes are also discussed. Secondly, a constitutive model considering dynamic compressive and tensile failure is applied to analyze blasting-induced fracture propagation in coal masses using LS-DYNA software. The bedding plane, which is 0.2m, 0.4m and 0.6m from the borehole respectively, is inserted into coal masses to explore its effects on the reflection and transmission of blasting stress waves. Parallel bedding planes and cross-joint planes are simulated to study fracture patterns during the blasting process. The results indicate that the transmission coefficient (Tcoe) of stress waves at a bedding plane constantly decreases with increasing distance from the bedding to the borehole, and an increased number of beddings can result in decreased transmission at beddings. The effects of double-borehole blasting are also studied at 0ms, 1ms, 2ms and 3ms of delay time, respectively. The results indicate that crack initiation and propagation between two adjacent boreholes are closely related to detonation delay time, and fracture networks between two boreholes form when the delay time of adjacent boreholes is more than 3ms.