Simulation of ground support performance in highly fractured and bulked rock masses with advanced 3DEC bolt model

摘要

The design of effective ground support is critical to the success of the next generation of large cave mines. Typically, the behaviour of rock in this setting is controlled by shear and opening movements along fractures induced by the excavation and cycles of loading and unloading during mine development and operation. Support of highly stressed fractured rock shows two important aspects: (i) in blocky or fractured rock the majority of the support deformation is localised at fractures or joints and (ii) the resistance to fracture shear displacement offered by support is important. These observations have led to the use of the discrete element method based three-dimensional bonded block model (BBM) to represent the rock and the hybrid bolt model to represent the bolt support. The hybrid bolt model is an improvement on the classical cable bolt model, which features a more realistic resistance to fracture shear displacement and allows bolt installation in a fractured rock mass exhibiting open joints. This paper presents the application of the BBM and hybrid-bolt numerical model to study the performance of tunnelling at depth under a caving-induced stress path. The effect of support pressure, bolts presence, and partial debonding of bolts, is explored. The influence of rock mass quality and support installation timing on the support efficiency is also investigated. It has been found that a small surface pressure is critical for tunnel performance. When a rock mass experiences large deformation and joint opening, local axial and shearing straining of bolts at joints intersection become important and can lead to rupture. Intense axial straining can be mitigated through debonding and intense shearing can be reduced through the use of bolts with higher shear resistance, such as rebars.