Modelling Rock Bridge Failure And Brittle Fracturing In Large Open Pit Rock Slopes.

ABSTRACT:

As large open pit slopes increase in depth, it is becoming increasingly necessary to investigate nonconventional slope failure mechanisms. The existence of rock bridges can have a significant effect on rock slope stability therefore, it is necessary to further our understanding of the impact of rock bridges and brittle fracture processes. In the first part of this study, the 3D lattice spring code Slope Model allows evaluation of the effect of rock bridges on the stability of a pentahedral or “non-daylighting” wedge. The geometry adopted simulates a 3D equivalent of a conventional 2D bi-planar wedge. As a preliminary analysis, various rock bridge percentages were simulated by the location of intact rock along the basal surface of the wedge. The results demonstrated that 2% rock bridges on the basal surface were required to stabilize the wedge. In the second part of this study, the staged construction of a rock slope containing a pentahedral wedge was modeled to investigate damage at the toe of the slope and the depth at which the wedge would fail. Significant damage at the toe was noted prior to daylighting of the basal surface of the wedge.



1. INTRODUCTION

As large open pit slopes increase in depth, with feasibility studies now underway for slopes over 1.4 km, it is becoming increasingly necessary to investigate nonconventional rock slope failure mechanisms. In massive brittle rock slopes, both natural and engineered (e.g. open pit mines), potential failure surfaces are often assumed as fully persistent continuous planes [1]. However, this is not the case for most slopes and where a certain percentage of rock bridges are present along the discontinuity, which increases the stability, ignoring their existence may lead to conservative design Many authors have demonstrated the importance of rock bridges on the stability of slopes [2-8].