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Old mine workings, mainly hidden galleries, goafs, shafts etc may pose a great threat to the local environment and also for future mine development. The present study mainly deals with delineation and mapping of old mine workings over Tikmani-Gareriya section, a part of east Basuria colliery, Jharia coal field, India using state-of-the-art 64 electrodes and 61 channel FlashRES-Universal electrical resistivity tomography (ERT). ERT data have been acquired along a line at 5m electrode spacing covering total profile length of 315m using Wenner, Schlumberger, Gradient and Dipole-Dipole arrays over a known old mine working. Further joint inversion of all combined arrays has also been carried out using 2.5D resistivity inversion program to combine the relative advantage of all arrays for producing superior results. The acquired data have been analysed using four different thresholds for all arrays with quality factors 15, 10, 5, and 1; each with 60mA current. 2D inverse resistivity models generated using Joint inversion of all combined arrays with quality factor 5 provides best result for delineation of coal pillars, galleries and goafs followed by Gradient, Schlumberger, Dipole-Dipole and Wenner arrays with same quality factor. Coal pillars have been identified with relatively high resistivity anomaly whereas galleries and goaf have been delineated with relatively low resistivity anomaly. The estimated range of resistivity variation of coal pillars have been well corroborated with published results. The results prove the efficacy of the ERT technique for detection of old mine workings.

Land subsidence is a serious problem in Indian coalfields due to old underground mine workings. Unfortunately, most of these are uncharted as no mine plans are available. The hidden galleries, goafs, shafts etc. may pose great threat for future mine development as well as to the local environment. The mine workings should be charted to undertake an effective preventive action. In the present study, 2D electrical resistivity tomography (ERT) technique has been used to detect underground mine workings, mainly air or water filled galleries. Initially, the whole exercise has been executed through a synthetic model study. Gaussian random noise of 5mV/A has been added with synthetic data to demonstrate field condition which provides realistic results. ERT survey was conducted over a part of Jogidih coal mine of Jharia coal field in India for a first time. Four electrode configurations, Wenner, Schlumberger, dipole-dipole and gradient were considered for this study. The results indicate the presence of sub-surface water and air filled cavity due to high resistivity contrast with surroundings.