A quantitative numerical assessment of blast-induced damage in an open pit bench blast using a propagating gas pressure boundary condition

Abstract

"One of the cost-effective methods used for rock breakage in mining is drilling and blasting. In open pit mining, blast-induced damage can reduce the level of stability of benches and pit slopes, which is a concern for the safety of mine personnel. Rock fracturing and fragmentation by blasting is the result of the coalescence of existing and new fractures (created by the blast) in the rock mass. The stress waves affect the rock mass in a few milliseconds while the effects of gas pressure last in the scale of hundreds of milliseconds and have a greater effect on rock fragmentation. The presence of in-situ fractures can have a significant impact on the extent of blast-induced damage beyond the intended area of the blast. These fractures are generally preferential paths of least resistance for the explosive energy. It is therefore necessary to account for the effect of the in-situ fracture network to reliably characterize fracture development and blast-induced damage. Discrete fracture networks (DFN) are representations of joint systems and can estimate the distribution of insitu fractures within a rock mass. The combined finite (FEM)/discrete (DEM) element method (or FDEM) is a useful tool to simulate the complex rock blasting process. FEM is used for calculating stress distribution and displacements before fracturing (static phase) and, once the fracture process begins, DEM is used for simulating the fractured medium (large displacement phase). The principal objective of this paper is to develop a DFN-based numerical FDEM model to assess the influence of gas pressure on blast-induced damage using a propagating boundary condition, which simulate the effect of gas pressure on a growing network of fractures. A two-holes open pit bench blast was simulated in 2D environment. In this simulation, gas pressure was applied on a propagating boundary (boundary of developed fractures). The numerical model is simulated based on rock and blast properties obtained from an operating open pit mine. The level of blast-induced damage was quantified based on the area of the blast damage zone and the intensity of blast-induced fractures. The results show that the propagating boundary condition provides a realistic simulation of blast holes interaction and blast-induced fracture development."