Numerical study on blast-induced fragmentation in deep rock mass

Abstract

As drilling and blasting technique is applied in deep mining, its practical performance with respect to rock fragmentation becomes a serious concern because high in-situ stress significantly affects the evolution of blast-induced rock cracking, and troubles such as over/under break and insufficient fragmenting may be arisen in deep rock excavation, leading to secondary problems related to the construction costs, ore crushing costs and mineral loss. In this study, the dependences of the blast-induced rock fragmentation on the changes of stress magnitude and stress dimension as well as the depth are investigated using the combined Finite Element modelling and image-processing. After calibrating the numerical model against the blast-induced rock fracture and fragmentation size distribution (FSD) in laboratory blasting test, a series of four-hole models are developed to simulate blast-induced rock fragmentation under various uniaxial stresses, confining pressures, hydrostatic pressures, and 3D in-situ stresses calculated by depths. The corresponding crack patterns are image-processed to provide quantitative insights into blast fragmentation under various in-situ stresses. Following, based on the findings obtained by integrated numerical modelling and image-processing, the effects of in-situ stress on the average fragment size and fragment aspect ratio, and the implications of current findings for practical blasting in deep rock mass are discussed. The results indicate that the blast-induced fragmentation becomes coarser and rounder, and the FSD range gets broader with the increase of stress magnitude and stress dimension as well as depth.