Numerical Investigation of Squeezing in Underground Hard Rock Mines

Abstract

Squeezing ground is one of the major challenges associated with deep, high-stress mining. In underground hard rock mines, these conditions are often a result of the presence of prominent structural features such as foliation inside the rock mass, which imposes mechanical anisotropy and leads to a nonlinear and anisotropic response of the rock mass to mining. Understanding this response of foliated rocks to various mining conditions is essential for managing the squeezing ground conditions. The complex behavior of a foliated rock mass requires the use of numerical methods to investigate the response of the rock mass to mining. Discontinuum numerical methods are frequently used to simulate anisotropic behavior, as they can explicitly represent the fractures. However, these methods present time and computational restrictions for large-scale models and complex mining geometries. These limitations can be overcome by employing anisotropic constitutive models in continuum numerical methods. This paper presents a methodology to investigate the failure mechanism of an intact foliated rock sample and foliated rock mass around an underground excavation utilizing the ubiquitous-joint model in continuum numerical methods. The paper also presents an approach that can be used to investigate the influence of varying interception angles between the foliation and excavation walls on the severity of squeezing ground conditions. The ubiquitous-joint model employed in FLAC3D accounts for the presence of weakness planes such as foliations in continuum material and can successfully reproduce the observed displacements and failure mechanism. The numerical modeling results were in good agreement with the closure strains recorded underground.