| Recent works in deep underground tunnelling have illustrated how the behaviour of the expected ground conditions can differ from those assumed (Kaiser 2005 & 2006). One of the reasons for this deviation is a result of structural features such as joints, bedding planes or foliations, facilitating the stress-driven rock mass disintegration process in areas that would not normally be considered.;This thesis focuses on the use of simple tools, namely the finite element program Phase2 to assess the influence of structural features on excavation stability. From this work, previously proposed joint orientation factors (i.e. Factor B in the stability number N') are assessed/back analysed and an Orientation Reduction Factor (ORF) based on a modification to the Stress Reduction Factor (SRF) proposed by Barton et al. (1974) is developed to assist in the design of circular tunnels in anisotropic rock.;In addition, modelling methodologies are presented which extend the conventional analyses carried out in Phase2 to incorporate joint networks. Relationships are also proposed to allow for continuum modelling to take rock mass bulking into account. |
