Analogy between indentation and blasting tests on brittle rocks

Abstract

Analogy Between Indentation and Blasting Tests on Brittle Rocks This paper presents a common mechanism of breaking quasi-brittle rocks either by drilling and blasting or by indentation. Only minor modifications, to account for the prevailing boundary conditions pertaining to either one of these cutting processes, are required. Rock breakage by drilling and blasting or by indentation is based on the formation of a heterogeneous stress field due to the application of concentrated loads either by the indentor or by the detonation of the explosives. Rock behavior varies according to the stress level generated into the material. In the high stress zone it is plastic or pseudoplastic. In low stress region, failure is of the brittle extension type. In indentation the formation of a confined plastic zone is essential before chipping. However, for blasting plasticity is not necessary to occur prior to chipping because the high pressure gases that are generated from the explosion are usually quite sufficient — under suitable conditions — to create failure by extension cracking. Energy consumed in these rock cutting processes is a function of the relative amount of fines produced and their size distribution (or degree of fineness). Further improvements in rock breakage efficiency can be achieved by the proper choice of the important parameters for the specific techniques. The above analogy can be extended to other well known rock testing and breakage techniques.