Estimation of the change in hydraulic conductivity above mined longwall panels

The change in hydraulic conductivity (K) above subsided longwall panels at underground coal mines is determined using a data base of pre-mining and post-mining K measurements made at multiple locations down the depth profile at each of a number of sites worldwide. Results show that, following caving of roof strata, there is a clear difference in the magnitude of changes in K above and below the top of the collapsed zone. Within the collapsed zone, relative increases in K are larger, even when taking account of measurements made in potentially unsaturated strata. A generalized conceptual model is presented for K change above subsided longwall panels. These results form a third independent database supporting the height of desaturation reported in an earlier study.