Impact of geotechnical factors on the secondary extraction of coal in the Witbank and Northern Highveld Coalfields, specifically related to safety.

Abstract

This report describes a literature review that identified geotechnical factors impacting on unplanned secondary coal extraction. These factors are grouped into nine broad classes of factors; namely, stratigraphy, rock /coal engineering properties, spontaneous combustion, discontinuities, igneous intrusions, collapse of previous workings, hydrology, stress environment and the primary mining parameters. It was found that for underground extraction stratigraphy, igneous intrusions, collapse of previous workings and the stress environment have the most impact on the rock mass behaviour (i.e. the roof caving and rock burst potential, rib and pillar stability, floor heave and roof / surface subsidence), roof support (both on a mine- and panelscale) and explosions/ignitions (gas conditions, as well as spontaneous combustion). For open cast extraction the stratigraphy, igneous intrusions, collapse of previous workings, the stress environment and the primary mining parameters had greatest impact on the rock mass behaviour (slope and high wall stability and floor heave) and explosions / ignitions. Selected collieries were then visited in order to quantify the impact the factors may have on resource/reserve estimation and safety.