Pot-hole subsidence in Son-Mahanadi Master Coal Basin

Pot-hole subsidence is an abrupt depression of local ground surface, which occurs due to sudden collapse of the overburden into an underground void. Pot-hole subsidence is a common form of subsidence in Jamuna and Kotma, Hasdeo and Bisrampur areas of Son-Mahanadi Master Coal Basin. Data of 34 cases of pot-hole subsidence were collected from the above areas and analysed from stand point of their causative factors, prediction, mechanism, and suggested mitigative measures. Analysis of these cases revealed that shallow depth, geological discontinuities, weak and saturated overburden are the main causative factors for the pot-holing phenomenon. Movement of eroded materials from saturated and weathered overburden with water along a fault plane into the underground bord and pillar development led to the formation of a pot-hole. Risk of pot-hole subsidence is high when the pot-hole potential ratings of causative factors are between 80 and 100. Suggested mitigative measures of pot-hole subsidence in bord and pillar development as well as unapproachable depillared workings include maintaining a minimum of 15 m un-weathered hard cover, controlled width and height of drivages, installation of suitable support system, back-filling, grouting of underground voids, etc.