Methodology Development to Incorporate Anisotropy in Slope Stability Analysis at Los Bronces Mine®

Abstract

ABSTRACT: The rock mass strength depends on a combination of non-persistent discontinuities and blocks of rock mass. Currently, the representation of the strength for slope stability analysis includes the joints sets (structural domains) with preferential orientations that generate unfavorable stability conditions. For the limit equilibrium stability analysis of slopes the strength of the anisotropic rock mass is estimated by means of an anisotropic rosette and the respective rock bridge percentage. This work focusses on providing guidelines for Los Bronces Mine to estimate the directional resistance according to the structural domain and slope design. First, it is created a discrete fractures network (DFN) using a robust structural database that represents the probabilistic distribution of each joints characteristic, i.e., orientation, persistence and intensity. Once the DFN has been established, it is possible to characterize the structural condition of the rock mass and estimate the equivalent structure that controls the slope failure. This process is carried out through two-dimensional continuous numerical modeling with explicit structures and the obtained indicators of slope stability. Next, the results of the numerical model are compared with a two-dimensional limit equilibrium analysis, allowing to establish the characterization of the anisotropy rosette and the rock bridge percentage. 1. INTRODUCTION it is important that when studying rock mass geomechanical behavior in slopes, its characterization includes the effect of discontinuities and their possible effects on stability at both the inter-ramp and global scales in an open-pit mine. Structural domains play a significant role in this study, representing in some way the strength of the rock mass, whose preferential orientations promote the formation of instabilities. The orientations of the discontinuities create a kind of network that translates into a final rupture surface, where rock bridges define an equivalent structure or possible instability mechanism. The final rupture surface includes both discontinuities and rock bridges, allowing the definition of an equivalent structure (Fig. 1). Generally, to estimate the shear strength of these equivalent structures (which conditions slope stability), a stepped path simulation is developed considering the properties of structures oriented sub-parallel to the slope (unfavorable).