The existence of geological discontinuity significantly affects deformation mode of rock slopes shaped at open-cut and open-pit mines. The aim of this paper is to evaluate the behavior of rock slope with geological discontinuity by using FEM with joint element. We conducted elastic analysis, elasto-plastic analysis and coupled-analysis of steady saturated flow and deformation of rock, considering how rock slope geometry, failure occurrence around the toe of rock slope and existence of underground water affect the frictional sliding of rock mass along discontinuity. In the analyses, Poisson's ratio of rock mass and friction angles of the discontinuity were considered as variables for open-pit and open-cut models, respectively. The elastic analysis showed that the sliding of discontinuity due to excavation was largely affected by both Poisson's ratio and initial stress state of rock mass. Elasto-plastic analysis showed that the sliding of discontinuity was largely affected by the friction angle of the discontinuity due to failure occurrence around the toe of rock slope. Furthermore, the coupled-analysis showed that underground water pressure also contributes to the sliding of discontinuity depending on Poisson's ratio. By the proposed method, we laid the foundation for understanding the rock slope behaviour with geological discontinuity.
The stability assessment of huge rock slope formed by OC (open-cut) and OP (open-pit) mining is of fundamental importance in terms of stable production and safety operation. The most important thing in the stability assessment is to evaluate whether rock slope is stable or not at present. Thus understanding the mechanical behavior of rock slope is indispensable. Especially, if the deformation behavior of the rock slope in the stable state is predicted, the comparison of the predicted rock slope behaviour with in-situ observations by such as extensometer, APS or GPS, could make us possible to access the stability. As one approach for such prediction, application of FEM (finite element method) analysis has been proposed by Kaneko et al. [1]. Generally, in the proposed FEM analysis, the rock mass was assumed to behave as homogeneous, elastic medium in a stable state. However, such assumption may not be applicable for the rock slopes with predominant geological discontinuity, which are found in some of OC and OP limestone mines in Japan where slate or schalstein exist under limestone as bed rock [2]. In the case, limestone is left to prevent the bed rock from weathering. Thus rock slope with geological discontinuity is no longer homogeneous and, thus, it is reasonable to evaluate the influence of the geological discontinuity on rock slope behaviour. Additionally, when the existence of geological discontinuity is considered, failure occurrence around the toe of rock slope and presence of underground water behind the discontinuity are also important. Thus, to analyze the rock slope behaviour with geological discontinuity, we developed a new numerical simulation code based on FEM with joint element. In the proposed code, it is possible to conduct elastic analysis, elasto-plastic analysis and coupled-analysis of fully saturated steady-flow and deformation of rock mass.
