Influence of natural discontinuities and mechanical properties on the fragmentation of marble by blasting in Central Africa

Abstract

This research focuses on the influence of natural discontinuities and mechanical properties in the fragmentation of marble by blasting. These natural discontinuities and mechanical properties are the parameters which are difficult to control and which considerably influence the fragmentation of marble after blasting. This paper aims at predicting the fragmentation of the Bidzar quarry rock, the only marble quarry in Central Africa, while improving the knowledge on it. This quarry has been facing problems of fragmentation of marble blocks for decades, which requires secondary firing and incurs enormous costs. The Kuz-Ram method was used for this study. The dip of the discontinuity planes, the compressive strength, the distance between the discontinuities and the density of the discontinuities are the operational parameters that were used to study the influence of natural discontinuities and the mechanical properties of the rocks on the fragmentation after firing. This work consists precisely in studying the pullability as a function of the dip of the discontinuity planes, then the fragmentation as a function of the powder factor, the compressive strength and the drilling mesh. The results of this study were compared with those of the other authors. Qualitative and quantitative studies were carried out in order to highlight the influence of natural discontinuities and mechanical characteristics on fragmentation. The fragmentation pattern of the Bidzar quarry was examined and compared with those obtained in other regions of the world, namely, Northern Europe, Central America, South-East Asia and West Africa. The variation in the intensity of fragmentation caused on the one hand by differences in the dips of the firing planes and their compressive strength, and on the other hand by the variation in the drilling mesh was also discussed. The prediction test was carried out with seven plans of existing discontinuities in the Bidzar quarry and at different mesh sizes in order to estimate the distribution of the fragments of marble thatcan through the crsuher after being fired.Several suggestions were put forward for the evaluation of the fragmentation. Three practical tables were created to predict the result of the shot. The specific graphs, which were proposed to analyse fragmentation in this quarry, made it possible to assess the quantity of fragments passing through the crusher after firing. Predicting fragmentation by considering the dip of the firing planes and the powder factor can effectively optimise the fragmentation of the rocks by blasting and achieve the desired result..