The crosshole seismic reflection method in opencast coal exploration

In opencast coal exploration in the UK, a dense grid of boreholes is drilled to provide the necessary information on the quantity and quality of coal reserves and on the geological structure. Typically, borehole spacing is 40- 60 m, but it may be reduced around faults or where there are old room-and-pillar mineworkings. Even with this density of boreholes, it is not possible to detect faults with throws less than 2-3 m, and these can pose a hazard to stability during excavation which may be particularly critical at site boundaries. Also, estimates of the quantity of coal reserves could be improved if old mineworkings were located more accurately.