State of the art dimensioning of shield support to optimise longwall roof control

Basic rock-mechanics research has always set itself the target of improving roof control measures at the coal face. The results of this work frequently led to the development of new support equipment. Between 1999 and 2003 a series of underground investigations was carried out as part of a DSK RD only if this critical tip-to-face distance is exceeded can roof falls occur. In order to prevent roof falls the shield supports have to be specifically chosen for each face in such a way that the critical tip-to-face distance is never exceeded under any operating conditions. If the tip-to-face distance is allowed to exceed the critical threshold, the frequency with which roof falls occurs can be predicted using an empirical equation. From time to time, however, the strata are stressed to such a degree that the technical capabilities of the support system are not sufficient to keep within the critical tip-to-face distance. Roof falls will then be unavoidable. This set of circumstances produces a further set of planning requirements. Where in the strata is there a suitable layer of rock above the coal seam for optimum roof control? Will the extension range of the supports still be suitable for this strata layer? The paper provides answers to these questions, presents the results of the recent R&D work and uses practical examples to explain how these state of the art calculation methods can be used.