Numerical modelling of blast-induced fractures in coal masses under high in-situ stresses

Abstract

Borehole blasting is a technique widely applied to form fracture networks in coal masses. There are many original cracks in coal masses, such as bedding planes and cleat planes. Coal masses are also subjected to high in-situ stress deep underground. However, the effects of pre-existing cracks and in-situ stress on blast-induced fractures are not well understood. In this paper, the isotropic and kinematic hardening plasticity model considering compression and tensile failure is introduced to numerical models, and the contact interface is used to simulate the effect of jointed planes on coal-mass blasting. The effects of jointed plane, constant in-situ stress and lateral pressure coefficient on blast-induced cracks are explored, and the relative peak displacement (Δup) of jointed planes is considered as the basis for determining jointed plane failure. The results indicate that blast-induced cracks tend to expand along jointed planes in the coal mass; the in-situ stress enhances the compression effect and weakens the tension effect in the radial direction of the borehole; and the jointed plane failure zone in coal masses decreases with increasing in-situ stress. The lateral pressure coefficient also has a distinctive influence on blast-induced crack expansion.