Abstract:

Crush pillars are commonly used in the intermediate depth platinum mines in South Africa. These pillars are designed to crush in the stope faces. This generally leads to stable conditions by preventing "back breaks" whilst allowing for higher ex-traction ratios. In most mining operations, the design of the crush pillars is based on trial and error. As the pillar strength is unknown, the pillar sizes are adjusted to obtain the desired behaviour. Pillars of different sizes, resulting in unfavorable behavior, are nevertheless found on most operations. Occasionally these pillars fail violently in the back areas, resulting in damaging seismicity. The objective of this paper is to simulate the behavior of crush pillars to obtain a better understanding of the key components determining their behaviour. Furthermore, it was aimed to develop a simple and effective tool which can simulate crush pillar behaviour on a mine wide scale. An analytical model was derived to calculate the residual average pillar stress values of the crush pillars. The values predicted by this model were compared to the numerical simulations and actual underground crush pillar stress measurements. The simulations illustrated the impact of mining depth and pillar size on pillar behaviour.

1 INTRODUCTION

During the past four decades, several studies regarding the behaviour of crush pillars were conducted in an attempt to better understand and predict the behaviour of these pillars. Crush pillar layouts nevertheless remained essentially unchanged during this period. In this paper, the behaviour of crush pillars was evaluated using a specialized numerical modeling tool. Various parameters were assessed including mining depth, pillar width, pillar height and pillar size.

2 TYPICAL CRUSH PILLAR LAYOUT

A typical mining configuration for a crush pillar layout consists of pillars being positioned either adjacent to raises / winzes (dip mining) or strike gullies (breast mining).

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