Numerical Investigation on the Impact of Drift Geometry Representation on the Assessment of Wedge Formation Using DFN Modelling in Underground Hard Rock Mines

Abstract

ABSTRACT Geological discontinuities have a large impact on the rock mass behavior in underground excavations. Under low stress conditions, structurally controlled wedge failure is one of the most critical types of rock instability. The stability analysis, in this case, is essential to consider both the rock mass fracture network and the geometry of the opening. However, current wedge stability analysis tools do not typically examine the detailed geometrical characteristics of the rock discontinuities and the excavation shape in 3D. This paper reports on the development of a comprehensive and more rational numerical approach to assess wedge formation around underground mine openings. The approach considers the structural rock mass complexity using Discrete Fracture Network (DFN) modelling and the detailed 3D underground excavation profile obtained from surveying. The developed methodology was successfully applied to estimate the formation of wedges around an excavation in an underground mine. A detailed investigation on the 3D profile and shape of the excavation indicated that an oversimplification of the excavation geometry in the stability analysis can result in inadequate assessment of wedge formation. Further analysis allowed to identify elongated wedges that may not be critical from a stability perspective and wedges that were not entirely formed in the DFN model but may still be critical for the stability of the excavation. INTRODUCTION Under low-stress conditions, the stability of mining excavations is frequently controlled by rock discontinuities (Hoek et al., 2000). Wedges are formed by the intersection of more than two discontinuities on the walls of an underground opening. The structurally defined rock blocks can fall or slide toward the excavation. The most common wedges in the field are tetrahedral blocks defined by the intersection of three fractures and the surface of the underground opening (Windsor, 1999). Under these conditions, analyzing the size distribution and probability of occurrence of wedges is critical for the design and support of underground excavations.