The Influence of Caprock on Blast Fragmentation Distributio

This dissertation describes the development of a small-scale model of a caprock-laden quarry blast and discusses the results from that testing. The purpose of this testing was to provide insight into the reasons for poor caprock breakage during blasting.;Small-scale test blocks were poured using a weak mortar mix to represent a limestone formation at a small scale. A cold joint was created in the upper portion of the test specimens to represent the bedding plane that separates caprock and substrate layers in a caprock-laden limestone bench. The scale-model test blocks were blasted using detonating cord. The primary configuration for this work was a single blast hole at a 4" burden and spacing from the outside corner of the test block. The blocks were loaded with detonating cord, and initiated from the bottom. Following blasting, surface breakage of the cap layer was photographed and collected for sizing. Following collection of the cap fragments, substrate breakage was photographed and collected for sieving as well.;Test blocks fragmented well in the substrate portion and poorly in the cap layers. Cap breakage was typically limited to single-digit fragment populations. Annular fracturing sometimes created uncharacteristically large fragments that exceeded the burden and spacing of the blast hole and explains the presence of uncharacteristically large boulders in the field.;This testing provided insight into how a massive, solid layer reacts when blasted from below. Cap breakage remained poor regardless of typical blast hole design. The results of this work indicated that the caprock fragmentation and the substrate fragmentation need to be treated separately by blasters and engineers.