Review and interpretation of primary floor failure mechanism at a longwall coal mining face based on numerical analysis

Abstract

This paper describes the conceptual model of primary rock failure mechanisms in the floor ahead of the longwall coal mining face based on underground observations and numerical modelling. During longwall mining, the stress fields and displacements of strata are constantly changing. High stress concentrations ahead of the longwall face can initiate fractures in the rock floor that can, under unfavourable stress conditions, develop into secondary floor failure, where large displacements of strata can occur. Severely broken floor strata or floor heave can seriously interfere with mining operations. Underground observations indicate that the sub-vertical shear fractures and the shear failure along the bedding planes in stratified rock are the most common fracture types observed in the rock floor below the longwall face. To explain how these fractures occur, basic principles of rock failure mechanism are applied to an overstressed rock subject to stress concentrations typically found at the longwall face. The computational simulation of the progressive longwall mining operations was undertaken in stratified rock to model complex stress distributions ahead of the longwall face and to simulate the rock failure in the mining floor. The model indicates that the shear fractures and the bedding plane failure dominate the floor failure ahead of the moving longwall face, as was observed underground.