This study has formulated a geotechnical and hydrogeological model of the Wintinna Coalfield which satisfies the following objectives: - to provide answers to the hydrogeological and geotechnical questions raised by Fluor in their mining study;...
This study has formulated a geotechnical and hydrogeological model of the Wintinna Coalfield which satisfies the following objectives: - to provide answers to the hydrogeological and geotechnical questions raised by Fluor in their mining study; - to provide confirmation of Fluor's mine design parameters; and - to provide sufficient information to allow further detailed mining studies. Fluor's mining study has provided design concepts and cost estimates for a 2 or 4 Mt/a underground mine and a 6 Mt/a open cut mine. Mining was assumed to commence in the area adjacent to the Arckaringa Homestead and to then progress in a north-easterly direction. For underground mining it was assumed access would be via shafts with the possibility of a decline if geotechnical and hydrogeological conditions were suitable. It was assumed that all coal seams except the Isolation (the top seam) could be extracted with development via continuous miners and coal mining by longwall techniques. Panel development would utilise single entries. Open pit mining would be carried out using a combination of methods. The Bulldog Shale, at the top of the sequence, would be drilled and blasted then excavated by an electric shovel into a mobile crusher and conveyed to the dump. Bucketwheel excavators would be used to remove the top 15 m of surface soils and weathered shale, and the Mesozoic sands. The coal measures would be drilled and blasted then handled by shovels and trucks for delivery to the dump (interburden) and in-pit crusher (coal). In-pit dumping would commence as soon as practicable. These proposed mining methods entailed a number of important assumptions and highlighted a number of areas where the geotechnical and hydrogeological aspects were critical. These were: UNDERGROUND MINING - all coal seams and surrounding strata are of sufficient strength for underground mining; - for underground mining, the low competence of the Permian rocks may prove troublesome; - groundwater inflow to an underground mine would not be excessive (greater than 4 Ml/day); - shaft sinking/decline construction is feasible in the bottom sections of the Mesozoic sands; - all coal seams could be extracted. OPEN CUT MINING - dewatering of the overburden is feasible to allow safe, efficient open cut mining and negate potential problems with pit walls and spoil dumps; - hydrogeological and geotechnical constraints permit overall highwall slopes of 38 degrees, and overall operating face slope angles of 12 degrees. Coffey's scope of work and resultant field, laboratory and office investigations were formulated to address these specific areas.
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