Physical stability of iron ore caves: geomechanical studies of a shallow underground cave in SE Brazil

Abstract

Caves hosted in iron formations are attracting considerable interest due to their scientific and environmental value. Some of these caves are located in or near iron ore mine sites, which represent an important source of income to Brazil. However, the Brazilian legislation requires speleological studies that currently have an impact upon ore reserves and environmental licensing processes. The aim of this study was to apply conventional geotechnical empirical approaches to a cave located within the grounds of an iron ore mine in the Iron Quadrangle and validate it with numerical modelling, to ensure the method’s applicability to natural caves under mining activity influence. These studies comprised the mapping of structural, geotechnical and geomechanical features of rocks hosting and surrounding the cave and to propose geotechnical domains. Field data collection covered the geotechnical parameters necessary to calculate the characteristic Mining Rock Mass Rating (MRMR) for each geotechnical domain, and to evaluate the stability conditions using the stability index or hydraulic radius of the cave. These geotechnical parameters were then used to calculate the physical parameters used in two-dimensional numerical simulations to verify the good stability conditions of the cave, corroborating the adequacy of Laubscher’s diagram. The results of this study, although comprising only one cave, suggest that Laubscher’s diagram is applicable for assessing the geotechnical behavior of iron ore caves.