Influence of Joint Conditions and Blast Design on Pre-split Blasting Using Response Surface Analysis

Blasting is a major method of excavation in mining, civil construction and infrastructure projects. The integrity of the rockmass of the final wall after excavation is important for the stability and economics of the operation. Perimeter blasting achieves a planned surface of the rockmass. The pre-split is one such technique, deployed when there is no free face and, thus, involving several interactions of rockmass properties, including strength, joint spacing and joint orientation, with respect to blastholes, blast design, explosive configuration, blasthole deviations and other variables. The mechanism and models of the pre-split are perfunctory, particularly in defining interactions of pre-splitting variables. The basis of pre-splitting vis-à-vis dominant variables affecting performance is, accordingly, discussed here. Since the half cast factor, generally used for damage assessment, has its limitations, the index of blast damage has been compared while modelling performance. Models using response surface analysis for pre-splitting, for both blast damage index and half cast factor, were developed using historical data. The angle of the blasthole with respect to the major joint orientation, spacing of the joints, blasthole spacing, drill deviation, linear charge concentration and compressive strength has been used to compare the above-mentioned damage criteria. Blast damage index has been found to be a better predictor for determining rockmass damage due to blasting. The desirability of the variables deployed has been determined using optimization procedures. A fresh impetus to pre-split studies is expected to provide a ground for future research, particularly studies using advanced computational and numerical algorithms.