ON THE EFFICACY OF SOME CONTOURING TECHNIQUE FOR COAL SEAM THICKNESS MAPPING

抄録

The Indian Standard Procedure for detailed coal exploration, to enable mine planning, translates into drilling of boreholes at 400m spacing on a square grid. Isochore maps depicting seam thickness variations are prepared contouring the seam thickness met in boreholes using, till recently, triangular plate or three point technique. With increasing availability of computerized contouring techniques, an exercise was undertaken to examine the relative efficiency of some of these methods. Actual measurements of vertical thickness of a fully exposed coal seam in an underground mine, made at spacing varying from 5m to 40m in an area of 0.96 sq.km. were hand-contoured to represent the ‘actual’ seam thickness variations. A transparent overlay of square grid at 400m spacing was prepared for the nodes to represent borehole locations. The grid-overlay was placed at six different orientations over the‘actual’isochore and the seam thickness in boreholes for each case were simulated at nodes.
These simulated borehole thickness data were, in each case, contoured through computer programs employing Triangular Plate, Polynomial Regression, Double Fourier, Cubic Spline and Krigging techniques. The results were evaluated qualitatively as well as quantitatively at sub-nodes at 80m intervals.
It was indicated that the krigging technique produced the most efficient contours with reference to‘actual’ isochore in all the cases. The change in the orientation of the borehole grid was not seen to substantially affect the accuracy of results.