Influences of foliation orientation and lateral stress difference on the deformation and fracturing of a thin?layered rock around underground excavations: insight from multi?axial loading tests

摘要

Layered rocks usually show anisotropy in their deformation and failure characteristics. The anisotropy is mainly caused by the orientation of thin-layered structure (e.g., bedding or foliation). Thin-layered structures are likely to fail, thus jeopardizing the stability of underground excavations. Under different bedding or foliation orientations, the surrounding rock mass will represent different mechanical responses with changing depth. Due to the limitation imposed by testing machine performance, most studies focused on the mechanical properties of the layered rock under conventional loading conditions, which partially reveal the mechanical properties influenced by bedding (foliation) orientation of the layered rock subjected to multi-axial loading. To overcome these limitations, a series of true triaxial compression tests on a steeply-dipping thin-layered rock taken from a deep metal mine were conducted in two cases of foliation orientation in this research. The results show that the lateral stress differences (sigma(2)-sigma(3)) have significant effects on the strength and failure of this rock at different foliation orientations, and indicate that, in tunnel design, the angle between the tunnel axis and foliation strike should be as large as possible to maintain the stability of the tunnel to the greatest extent. The findings from this research show anisotropic rock behavior around underground excavations under various stress and foliation orientation states, and help designers to optimize tunnel orientation and prevent large anisotropic deformation.