An investigation of the rock mechanics aspects of a system of short face in-seam development for subsequent longwall retreat extraction

Abstract

The research work undertaken in this study was sponsored by the National Coal Board and consists of an investigation into the rock mechanics feasibility of a method of in-seam development by short faces with a centre pack, creating two roadways for subsequent retreating. An elastostatic solution by an approximate analysis has been given for this method of advancing for roof behaviour and to obtain pack load with face advance and the ribside abutment pressure distribution. The elastostatic analysis for the short face advancing situation has been done for anhydrite (setting) and conventional (non-setting) packs. A method is given for assessing the ribside abutment loading during subsequent retreating and loads in the goat. The floor loadings obtained during short face advancing and subsequent retreating have been used for a floor stress analysis and for predicting the post-failure viscoelastic floor heave during retreating. Some anhydrite properties relevant to the analysis have also been investigated in the laboratory and a formula for estimating the in-situ strength of anhydrite packs has been given.