Análise de tensões no método de lavra abatimento em subníveis, mina Ipueira 4, Andorinha, Bahia.

Abstract

This research concerns stress analysis at a panel in Ipueira 4 Mine. The mine is located at Andorinha County, State of Bahia, Brazil. Chromium mineralization occurs in a sill about 8 meters thick. The orebody dips steeply, and is crossed by a complex faults system, that causes its discontinuity, and may render it sub horizontal in some sectors. The mining method sublevel caving is adopted. Immediate caving does not occur in some panels, particularly in those exhibiting low dips. The panels are blasted in fans, longitudinally in retreat, from the borders to the center, where is located the access ramp. The panel analyzed is located at a depth of 320 meters, where the orebody is sub horizontal, dipping about 8 degrees east. The development of the panel has been accomplished by means of six drifts, separated by long pillars, 8 meters wide by 4 meters high, approximately. The panel is about 200 meters long by 70 meters wide. Production in the panel started in 2003, and is expected to continue until mid 2006. Numerical modeling has been done in the two dimensional geometry, under elastic regime, using the boundary element Examine2D program. For the three dimensional analysis the boundary element program Examine3D has been used, also under elastic regime. The mechanical properties of the rock mass have been estimated from laboratory data combined with geo-mechanical rock mass classification. The in situ rock mass stress is assumed to be of the gravitational type, with K factor of horizontal stress components taken equal to 1.0. Stresses and Hoek-Brown factors of safety distributions are analyzed for two mining stages. The results indicate overall pillars stability and zones of high stresses concentrations close to the access ramp and to the stopes. The results of 2D and 3D numerical analysis have been compared, in order to establish the conditions of applicability of bidimensional models for anticipating the stress distribution around the drifts, especially in the critical regions, which are close to the stopes and to the intersections with the access ramp.