Abstract

Sill pillars are used to divide vertically extensive orebodies into mining blocks to allow concurrent mining operations to occur. Sill pillars also provide regional stability to an area and are usually one of the last volumes of ore to be mined. This paper describes the decision process for positioning the overcut development within a sill pillar while considering operational and geotechnical issues.

There are three possible scenarios for the placement of the overcut development: in the sill pillar, in the backfilled stope directly above the sill pillar, or a combination of the sill pillar and backfill. Numerical modelling (finite element) was used to aid in the decision-making process for the location of the overcut development. In addition, this modelling was used to understand the potential failure mechanisms and forecast the mining conditions during development and production in a sill pillar. Results from the numerical modelling have shown that mining in the adjacent blocks caused a decrease in stress in the sill pillar. Potential failure mechanisms would include the deformation and unravelling of the overcut development and the failure of the longhole stope walls due to this decrease in stress.

To apply to an operating mine, the numerical model must be of sufficient detail to capture the mechanics of the problem yet be completed in a timeframe to support the decision-making process. Each of the overcut development scenario's operational strengths and weaknesses were evaluated alongside the numerical models to understand the implications of each development scenario. Using a combination of numerical modelling and operational considerations, the location of the overcut development can be decided to maintain safe access for underground personnel during the recovery of the sill pillar.