Influence of geotechnical conditions on explosive specific charge in Sri Lankan quarrying and tunnelling practices

Abstract

Quarrying and underground excavations carried out by drilling-and blasting is the most commen technique usued in sri lankan mining practice Although only a small amount of the explosive energy is efficiently utilized in rock blasting, the economics of subsequent processes such as loading, hauling and crushing are governed by the initial explosive impact on breakage of hard rock. Explosive consumption in the initial stage of rock breakage from the mass is expressed in terms of explosive specific charge or powder factor. Variations in geological and geo-technical parameters such as rock joint characteristics; strength of rock and rock mass rating (RMR) with varying geological characteristics is reflected in the variation of the specific charge of the explosive. Even though there is a large variation in geology over the Sri Lankan land mass only the metamorphic rock terrain has been considered, in studying the influence of geological and geotechnical properties on the determination of the explosive specific charge as an important parameter in blast planning and estimation. The paper emphasises the relationship of rock strength parameters and rock mass rating when estimating optimum explosive specific charge for economical quarrying and tunnelling practices in Sri Lankan conditions.