Prediction of rock slope deformation is significantly important for stability assessment. In particular, if the deformation under a stable state of a rock slope is successfully predicted, the slope stability can be evaluated by comparison of predicted and observed deformations. Based on this point of view, some researchers have successfully shown that the rock slope due to floor excavation in a pit -type mine can be expressed by elastic deformation. However, rock slope deformation due to excavation in the case of mountain type mine has not been cleared yet. In this study, the elastic deformation due to excavation of a mountain type mine was investigated by 2 dimensional (2-D) finite element method (FEM). Considering the possibility that the characteristics of deformation measured by extensometer show the dependancy on its insertion direction and location, the displacements along horizontal, tilted and vertical lines assuming the extensometers at the different insertion locations were simulated for various Poisson's ratios. In the horizontal and tilted directions, the rock slope formed is always extended by the progress of excavation. It is found that the magnitude of displacement tends to decrease with the increasing distance from the excavated region and the magnitude of displacement at small Poisson's ratio is greater than that at large Poisson's ratio. In the vertical direction, neither apparent increase nor decrease in the displacement with depth can be found and the magnitude of displacement at small Poisson's ratio is greater than that at large Poisson's ratio. Two locations of measurement by an extensometer were considered at the top of the slope and at the lower part of the slope. The extended deformation of rock slope was always found by an extensometer installed into the horizontal and tilted directions on mountain type mine. In addition, both those directions showed that the magnitude of relative displacement decreased with the increase in depth and Poisson's ratio. In case of the vertical direction, the rock slope formed by excavation showed predominant contraction and relative extension by an installed extensometer at earlier and subsequent steps of excavation, respectively. Magnitude of the contraction and extension at v of 0.4 and v of 0.1, respectively, were greater. The extensometer became insensitive to excavation with the progress of excavation in all directions of displacement measurement.

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