Strata deformation measurements on longwall coalfaces and their implications for design of powered support systems

Summary Recent developments in powered supports on British longwall faces include the advent of lemniscate designs, increased setting and yield loads, larger maximum extraction heights and a consequent rise in weight and cost. There was a requirement to examine the relevance of existing strata control theory to modern conditions. Measurements on five longwall coalfaces at four British collieries are described. Accurate measurements of support pressures, closures and inclinations, roof/floor convergence and lateral movement and hydraulic supply parameters were made with a digital data logging system. At one site magnetic extensometers were utilized to measure face and roof strains. Consideration of measured roof dilation and reclosure in conjunction with convergence provides a new perspective on the deformation mechanisms involved. The most important parameters governing strata conditions were identified as proximate lithology, foundation characteristics and adequate setting load densities. Recommendations are made regarding choice, design and operation of powered supports.