Strata monitoring investigations around longwall panels beneath the cataract reservoir

This paper describes the extraction of longwall panels in the Bellambi West Colliery beneath the Cataract water reservoir in the Southern Coalfields of NSW. These longwall workings were designed in accordance with the statutory conditions imposed by the Reynolds Commission of Inquiry, 1978, and worked in accordance with the conditional permission given by the Dams Safety Committee. The major conditions under which mining was permitted included: (a) submission of periodic mining plans identifying the geological structures encountered, (b) monitoring of strata behavior around mine workings and (c) water balance studies to be carried out in the mine workings beneath the water reservoir. The main monitoring program consisted of monitoring of geological structures, observation of the water seepage into the mine workings together with their sediment contents, and the measurement of surface subsidence and sub-surface strains. In addition, piezometric levels in the boreholes overlying the production districts were measured showing the fluctuation of the ground water level. Stress/deformation measurements were made on the longwall chain pillars to indicate their structural stability. Strata monitoring during the first three years of workings under the Cataract reservoir have indicated that the surface and subsurface subsidence and the strata displacements were within permissible limits and no water inflow was encountered as a consequence of coal mining under the Cataract reservoir. Based on these studies, the life span of the mine has been extended by eight years. © IMWA Springer-Verlag 2001.