The Deformation Modes of Rock Slopes due to Excavation in Mountain-Type Mines

摘要

This paper discusses an investigation of mining-induced elastic deformation of a cut rock slope formed in a mountain-type mine using a two-dimensional finite element method. The horizontal elastic deformation mechanism is discussed, including the effects of the Poisson's ratio, slope angle and progression of the excavation. The results show a clear dependence of the deformation modes characterized by extension, contraction or shear distortion of rock mass, on these three effects, in which the direction of rock movement at the surface due to excavation was opposite. Four effects contribute to the deformation mechanism in mountain-type mines: the Poisson effect (PE), the distributed load effect (DLE), bending effects and shear distortion. Forward surface displacement of the cut rock slope was found to occur during the early stages of excavation due to the release of horizontal compressive stresses due to bending effects around the middle of the mountaintop. As the excavation progresses, forward or backward horizontal surface displacement was found to occur due to PE or DLE, respectively, which depends on the Poisson's ratio in the subsequent stages of excavation. Asymmetric stress release due to excavation affects the horizontal deformation of the mountain, and induces a moment enhancing the backward displacement due to shear distortion. It should be noted that the direction of the surface displacement of the rock slope could change from forward to backward as the excavation progresses, even though the rock slope may be stable. This is very important in the interpretation of surface displacement monitoring using the Automated Polar System and/or Global Positioning System. In the interpretation of the internal displacement measured using extensometers, we should consider extension during the early stages of excavation, followed by slight contraction during the latter stages, as a sign of a stable cut rock slope in a mountain type mine.