ORIGINAL PAPER Modelling of Longwall Mining-Induced Strata Permeability Change D. P. Adhikary • H. Guo Received: 18 September 2013 / Accepted: 26 January 2014 Ó Springer-Verlag Wien 2014 Abstract The field measurement of permeability within the strata affected by mining is a challenging and expensive task, thus such tests may not be carried out in large num- bers to cover all the overburden strata and coal seams being affected by mining. However, numerical modelling in conjunction with a limited number of targeted field mea- surements can be used efficiently in assessing the impact of mining on a regional scale. This paper presents the results of underground packer testing undertaken at a mine site in New South Wales in Australia and numerical simulations conducted to assess the mining-induced strata permeability change. The underground packer test results indicated that the drivage of main headings (roadways) had induced a significant change in permeability into the solid coal bar- rier. Permeability increased by more than 50 times at a distance of 11.2–11.5 m from the roadway rib into the solid coal barrier. The tests conducted in the roof strata above the longwall goaf indicated more than 1,000-fold increase in permeability. The measured permeability values varied widely and strangely on a number of occasions; for example the test conducted from the main headings at the 8.2–8.5 m test section in the solid coal barrier showed a decline in permeability value as compared to that at the 11.2–11.5 m section contrary to the expectations. It is envisaged that a number of factors during the tests might have had affected the measured values of permeability: (a) swelling and smearing of the borehole, possibly low- ering the permeability values; (b) packer bypass by larger fractures; (c) test section lying in small but intact (without fractures) rock segment, possibly resulting in lower permeability values; and (d) test section lying right at the extensive fractures, possibly measuring higher permeabil- ity values. Once the anomalous measurement data were discarded, the numerical model results could be seen to match the remaining field permeability measurement data reasonably well. Keywords Field monitoring  Numerical modelling  Cosserat continuum  Underground permeability measurement  Packer testing  Mining-induced permeability 1 Introduction Reliable prediction and management of mining-induced water inflows and aquifer interference are major emerging challenges confronting the mining industry. The Australian coal-mining industry is facing intense public and political scrutiny and hence is required to operate with unprece- dented environmental accountability. The absence of robust and reliable analysis tools may significantly affect the industry’s ability to gain mining approval and licences, where significant aquifers, surface water or flooded work- ings are involved. Groundwater flow during longwall mining is governed by complex interaction between longwall caving and sub- sidence, pore pressure and permeability changes, and is influenced by site-specific in situ hydrogeological, geo- logical and geotechnical conditions. Generally, numerical modelling is utilized to predict the probable impact of proposed mining on groundwater. However, the lack of site hydrogeological data (such as pre- and post-mining strata permeability) may significantly affect the reliability of the modelling results. The D. P. Adhikary (&)  H. Guo CSIRO Earth Science and Resource Engineering, PO Box 883, Kenmore, QLD 4069, Australia e-mail: deepak.adhikary@csiro.au 123 Rock Mech Rock Eng DOI 10.1007/s00603-014-0551-7