PONTES, J.C.; http://lattes.cnpq.br/4572073364963892; PONTES, Julio Cesar de.
Résumé:
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.
