Abstract
Rock mass is an anisotropic material because of its heterogeneity and presence of discontinuities. It is significant to consider the influence of rock mass anisotropy on geotechnical design in rock slope engineering. This paper presents a case study that applied anisotropic models to analyze the rock slope stability in a box cut excavation at a mine site in British Columbia.
A site investigation revealed that bedrock at the excavation location was fine-grained siltstone. Structural trends were identified based on core logs. Uniaxial compressive tests on the rock cores and direct shear tests on the rock joints were performed to investigate the strength of rock and joint.
The rock slope stability was evaluated using the 2D limit equilibrium method (LEM). Anisotropic models were applied in the LEM analysis to study the influence of the presence of jointing orientation on slope stability. The anisotropic model included a Hoek-Brown criterion, representing the rock mass, and a Barton-Bandis shear strength criterion, representing the joints. Various dipping angles of critical joints were assigned in the model. The slope stability was also analyzed without rock mass anisotropy for comparison. The results showed that the factor of safety (FoS) for the analysis, without considering the rock mass anisotropy, was generally greater than three, which indicated a stable rock slope. In contrast, the anisotropic models showed that the rock slope did not meet the required FoS and was potentially unstable, requiring slope re-design or slope reinforcement. Applying the anisotropic models in rock slope stability analysis provided a methodology for optimizing the slope design.