Borehole Radar for Delineation of Unapproachable Underground Coal-Mine Galleries below Grand Chord Railway Lines

There are chances of railway lines being unsafe and thus directly affecting the safety of persons and goods due to the presence of old, abandoned and inaccessible mine workings below them. In the past, about 21 galleries in the leasehold of Kunstoria and Satgram areas of the Eastern Coalfields Limited (ECL), West Bengal and 33 galleries in the leasehold of Mugma area of ECL were driven below the Eastern Railway on the Grand Chord Howrah-Delhi railway line between Andal and Dhanbad. The abandoned mine plans of most of these galleries are not available and as such the exact locations of the galleries were not known. Keeping the above points in view, the present study was taken up for delineating the inaccessible and unknown mine galleries using borehole radar near Ratibati Colliery, Satgram area. A borehole radar survey has been conducted using an antenna frequency of 100 MHz along the six proposed railway sites. Six mine galleries were delineated in a radial distance varying from 4.5 to 5.0 m from the investigation boreholes and at the depths of 24, 27.5, 36.5, 51.5, 53.5 and 54.5 m respectively, from the surface. These mine galleries have been confirmed using direct non-coring drilling. It is also suggested that all mine galleries should be filled up with sand for the safety of the Grand Chord railway tracks in future.