Influence des discontinuités naturelles et des propriétés mécaniques dans la Fragmentation du marbre par abattage a explosif en Afrique centrale

Abstract

Natural discontinuities as well as mechanical properties are the difficult-to-control parameters that significantly influence the fragmentation of marble after blasting. In Central Africa, the Bidzar quarry is the only one producing marble, plagued for decades by block fragmentation problems, requiring multiple blasts that cause huge costs and environmental problems. The objective of this study is to predict the fragmentation of the Bidzar rock quarry and to improve its geological and mechanical knowledge using the Kuz-Ram method. Thus, blastability as a function of the dip of the discontinuity planes as well as fragmentation as a function of the powder factor, compressive strength and drilling mesh were studied. The results obtained show that, the rock quarry is heterogeneous, consisting mainly of fissured marble of medium hardness. Its dip is about 85°, its rock factor is 10.455 and it is class III, with a difficult blastability of 0.2654 kg/m . The marble from the Bidzar quarry is of excellent quality with an RQD of 93%. The fractures and discontinuity planes are spaced and of class ES2. The density of the fractures and discontinuity planes is low and of class ID2.The rock quarry is intercepted by a network of discontinuity planes marked by three families of direction, major (N30-40E, N40-50E, N160-170E), secondary (N10-20E, N50-60E, N80-90E, N140-150E, N150-160E, N170-180E) and minority (N00-10E, N20-30E, N40-50E, N70-80E, N100-110E, N110-120E, N120-130E, N130-140E). Finally, the variation in fragmentation intensity is caused by differences in the dips of the blasting planes, their compressive strength, and the variation in the drilling mesh. The level of fragmentation increases with the decrease in the dip of the blasting planes and inversely with their compressive strength. The result of the prediction of fragmentation after blasting in the Bidzar quarry as a function of blasting planes and the drilling mesh gives a productivity between 60.08% and 71.78% of the block that pass to the crusher. Blasting planes design whose compressive strengths are above 90 Mpa produce better fragmentation.