Stability Assessment of Stopping Operations in Friable Ore Bodies under an Open Pit Mine using Strength-based Mining Sequence Factor

A novel underground mining method is proposed to extract friable chromite ore bodies in weak and weathered limonitic host rock below an open-pit mine. The conventional underground methods do not instil confidence since GSI (Geological Strength Index) of ore bodies and host rock lies below ۳۵. Series of dimensions of transverse stopes along the strike are suggested based on a detailed analysis of multiple mining and backfilling operations by simulating ۳۶ three-dimensional numerical models. For each operation or sequence, a strength-based “Mining Sequence Factor (MSF)” is devised that helps quantifying its equivalent strength compared to in-situ conditions. This factor along with the average equivalent plastic strain (AEPS) developed on the pillars as obtained from numerical models is used to determine the safe operations with desired yearly production target. The paper provides an in-depth analysis of this method and suggests minimum pillar dimensions of ۴۰ m, whether in-situ or backfilled. The paper, in addition, lays the design of underground drives and their support system as per NGI (Norwegian Geotechnical Institute) guidelines and ۳D numerical studies, the performance of which is analysed considering distribution of stress and equivalent plastic strain.

کلیدواژه ها:

Friable ore and host rocks ، Mining under open pit ، Novel mining method ، Mining Sequence Factor ، Support system