Análise empírica de maciços rochosos para rochas com fins ornamentais.

Abstract

The liberalization of international trade which was implemented by the Brazilian government in 1990 made possible to import sophisticated equipment for the ornamental stones industry. That fact had a positive influence helping the country to become an important player in the international market of the ornamental stone economic sector. The Northeast region, mainly in its dry portion, has a large exposure of crystalline pre Cambrian rock, which has great potential for production of dimension stone granitic rocks. At present, important progress has been achieved in the ornamental rock industrial sector, and there are more than a hundred different types of rocks of commercial value for exporting already cataloged. In spite of that, the overall performance of Brazil in the international market has decreased to seventh in rank, having the country been surpassed by Portugal and South Africa. This research has the objective of suggesting technical procedures for the empirical analysis of rock masses suited for the extraction of covering stones. Generic aspects are treated in the search of more rational quarrying methods, with emphasis in the following characteristics: regional geology and geomorphology; mineral and petrographic aspects; and geotechnical characterization of the rock mass. The methodology adopted consisted in bibliographic survey and field observations. It has been possible to define the present situation of the sector of row blocks from the commercial and economic points of view; principles and techniques for estimating in situ stresses; evaluation of methods for rock mass classification oriented to ornamental rock; observation of geologic aspects and state of stresses at eight quarries. In order to prepare quarrying plans it has been concluded that the following sources of information should be used during the early stages of prospecting: analysis of previous works about the structural geology of the region; petrographic study in oriented rocks; analysis of topographic characteristics of the area; and analysis of rock cores. It has also been observed that rock mass classification systems oriented to dimension stones should use RQD index with caution, since it is generally equal to 100 in that case, and that Hoek-Brown failure criteria is useful in establishing the maximum limit of stress that the rock mass can withstand. The usefulness of Laubsher classification system in estimating the mean size of blocks is highlighted. The final conclusions include recommendations of practical procedures, which may be adopted for geologic exploration of dimension stone granitic rocks, according to their different genetic types.