Estudo da fragmentação em desmonte com explosivos na pedreira Queimadas - Pedraq.

Abstract

The main objective of the present dissertation is to analyze the fragmentation resulting from blasting at a quarry located at Queimadas County, in the State of Paraiba. The quarry is owned by PEDRAQ company. The rock, classified as granodiorite, is used for the production of crushed stone, which is consumed at construction sites in the Campina Grande region. The research work consists initially of a condensed review of the technology of explosives engineering, treating mainly of explosives properties, propagation of shock and elastic waves, rock fragmentation mechanisms, and design of blasting rounds. The field works involved the measurement of oversize rock blocks (blocks with at least one dimension larger than 070m), encompassing a set of ten primary blast rounds. The data from the measurement of oversize blocks was organized in a set of tables. The relationship between the volumes of oversize blocks with respect to the total volume of rock for each blasting round varied from 28 to 73 percent, with values over 53 percent for nine, among the ten blasting rounds studied. A topographic survey of the whole quarry was conducted, followed by a detailed mapping of rock mass joints, at both benches. The data from the topographic and geotechnical surveys were plotted in plan views and vertical sections. From the hemispheric projection of joint poles, two sets of sub-vertical joints were detected. The direction of those joint sets are approximately normal, with joint spacing around 5 and 9 meters. The bulletins of round blasts supplied by the company were analyzed. For the sake of comparison, the quantities of different types of explosives were converted into dynamic and semistatic energy. The energy per volume of rock blasted was plotted against the percentage of oversize blocks for the ten blasting rounds analyzed. From those graphs it has been concluded the major influence of rock joints density into the generation of oversize blocks. In order to improve fragmentation a reduction of bench height is suggested. Also, it is emphasized the importance of selection of explosive type considering joint spacing for different domains of the rock mass. From this study it has been shown the excessive generation of oversize blocks, with the need of extensive secondary blasting, causing air blast and fly rock problems, in addition to high drilling, explosives, and manpower costs.