Blast resistance of rocks–framework for the blastability classification of solid materials

Abstract

The rock blastability analysis reveals that the common blastability characteristic of rocks, namely, powder factor per fragmentation of 1 cubic meter of rock, is an indirect estimate of blast resistance. The review of the existing rock blastability classifications finds out that the comparison of these classifications is impossible due to different definitions of rock blastability, as the powder factor depends, ambiguously, on the rock hardness, explosion yield and blasting conditions. Explosibility of rocks is also often estimated as function of rock hardness factor on Protodyakonov’s scale. In this case, it is assumed that hard rocks are more difficultly blastbale than soft rocks with smaller value of hardness. In reality hard but brittle rocks, other things being equal, have smaller resistance to blasting and produce better fragmentation as against weaker clayey rocks. This is connected with sudden attenuation of blast-induced seismic waves in loose clayey rocks. The proposed method allows higher accuracy of rock blast resistance estimate thanks to inclusion of rock characteristics reflective of rock blastability. It s found that blast resistance of solids, including rocks, depends on the material constitution, structure and texture of a material. The blast resistance value is minimal in low-density and brittle rocks, for instance, coal, with low strength, and is maximal in dense and more plastic rocks. The proposed rock blastability classification grounded on the mechanics-based blast resistance index enables powder factor control and enhancement of blasting efficiency in surface and underground ore and coal mines.