ORIGINAL PAPER Mine Site Specific Longwall-Induced Permeability Changes: A Case Study Manoj Khanal . Deepak Adhikary . Brett Poulsen . Hua Guo Received: 1 October 2018 / Accepted: 19 February 2019 Ó Springer Nature Switzerland AG 2019 Abstract Mine site specific numerical models using representative hydraulic properties of various over- burden strata have been developed to investigate the effect of underground excavations on change in permeability in overburden strata. The developed models have been calibrated and validated against the mine site subsidence and mine water inflow data. The paper compares results obtained from a 3D finite element modelling with a 2D discrete element mod- elling. Each technique is demonstrated to have unique capabilities; the continuum method has efficiencies that allow three dimensional simulation while the discontinuum approach allows for the initiation and propagation of fractures allowing for the calculation of permeability from first principles. The comparative results between 3D simulation and 2D simulation are in good agreement. It has been noted that a well- defined 2D model can also represent the 3D numerical model in order to quantitatively estimate the height of connected fractures. The increase on the longwall panel widths causes the height of enhanced perme- ability to increase. Keywords Permeability  Longwall extraction  Underground coal mining  Interconnected fracture 1 Introduction During the process of longwall excavation the over- burden strata undergo fractures, deformation, delam- ination, shear and movements, induces fractures in the surrounding strata and hence changes the permeabil- ity. This process may interconnect various water bearing zones (aquifers) within the overburden strata with the mining voids (Denkhaus 1964; Gale 2008). In order to understand the effect of mining on aquifers and changes in site specific hydraulic characteristics that are unique to mine sites, it is essential to develop a mine site specific numerical model with a represen- tative hydraulic properties of various overburden layers, and understand how the mining associated fractures are developed and interconnected. In general, the disturbed overburden strata can be technically divided into three to four zones which are characterized by distinctive fracture and deformation behaviour of each zones (Guo et al. 2007). Figure 1 depicts an example. Height of each zone is a matter of interpretation among researchers and observations based on site specific parameters and is generally considered dependent on the longwall width, mining height, geology, depth of cover and overburden strata properties. Of these three/four zones the highly disturbed zones are the first two zones above the goaf (commonly defined as caved and fractured zones), hence the permeability changes are maximum in these two zones, and the remaining overlying strata are M. Khanal (&)  D. Adhikary  B. Poulsen  H. Guo CSIRO Energy, Queensland Center for Advanced Technology, 1 Technology Court, Pullenvale, QLD 4069, Australia e-mail: Manoj.Khanal@csiro.au 123 Geotech Geol Eng https://doi.org/10.1007/s10706-019-00842-z