The correct design of open pit mines depends, among other things, on the slope design at different scales, which must deal with the geotechnical stability and the safety of personnel and equipment. In this regard, the bench scale design procedures that rely on prediction of the spill length of failed wedges currently lack of a robust definition of the conversion from a solid volume of rock forming a wedge into a pile of broken material. At present, the assumption of a bulked density is the main consideration for estimating the maximum spill length of the broken material. This approach, however, disregards the inherent complexity of rock masses and the likely influence of the internal discontinuities and/or defects into the actual potential for disintegration of a failed volume.

The work presented in this article addresses a first approach to this issue by proposing the use of discontinuum numerical modeling codes (such as Itasca´s 3DEC) to estimate and define rules for the physical behavior of the spilled material once the kinematic failure mechanisms (planar in this study) are activated. The main objective of this study is an assessment of the final configuration of the spilled material, its volume, the final geometry of the slope, the spill length and establishing possible correlations of these variables with the rock mass characteristics. The study is applied to a limited number of rock masses, ranging from a very isotropic material with many joint sets within the failed wedge, to a very competent rock mass with only a few persistent discontinuities.

1. Introduction

The code KATS (Kinematic Analysis Tool for Slopes) is a tool developed by Itasca S.A. (the Santiago office of Itasca International Inc.), aimed at assessing instabilities caused by day-lighting wedges and planar failures formed when different structural sets interact with the orientation of a given slope [1,2].

The aim of this work is to check the geometrical assumptions adopted in KATS to calculate the spill length, which is "the extent of the spill that is originated by the failed (and broken) volume" [2] and it is frequently used as a reference to determine the berm width necessary for containment and therefore safety of the operation. A three-dimensional distinct element model (using the code 3DEC) [3] was developed to estimate the extent and pile shape of the failed material taking into account the rock mass strength and shape of the particles of material inside the planar failure.

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