Case study: Stability assessment in underground excavations at vazante mine-brazil

Abstract

Currently, most studies on stability of underground excavations include two separate analyses: the elastoplastic behavior of rock masses and/or kinematic analysis of possible wedges and blocks formed in the excavation walls. This paper presents a case study carried out at the Vazante Zinc Mine in Minas Gerais, Brazil, where studies on stability of underground excavations in discontinuous media included survey reports, laboratory tests and in-situ collected data. In this context, where galleries and mining stopes are excavated in discontinuous media, collapse events caused by the presence of discontinuities are common. First, the spatial orientation, geometric arrangement and mechanical characteristics of the discontinuities intercepted by the core samples were collected. The spatial orientation was based on guide layers, which are discontinuities with known dip direction and variable and dip. The geotechnical characteristics of the discontinuities were obtained by correlation with the roughness degree and the nature and weathering degree of the filling material. From there, the geological-geotechnical models were developed, which were the basis for the finite element analysis in discontinuous media of the designed excavations in the sections 13225 and 13300, between levels 210 and 345 of the mine. For comparison and complementation, wedge kinematic analysis and finite element analysis in equivalent continuous media were performed and, later, an arrangement for the reinforcement system was suggested. The results of these studies show that, in general, continuous models tend to be more conservative and have wider deformation zones, while discontinuous models are able to show in more detail where the displacements occur, and how the families of discontinuities affect the stability of excavations.