Extraction at higher depth of cover: retrospection of geotechnical problems and a recent case study

Understandably at greater depth 360m or beyond, the pillar w/h (width-to-height) ratios exceed the dimension for which the most widely known strength equations (in Indian mining condition, the CMRI pillar strength equation) were derived. Indian Coal Mines Regulations, 1957 suggests a minimum size 48m X 48m, centre-to-centre for depth of cover more than 360m. it is however pertinent to know the optimum dimension of a pillar in such situation. Although with large w/h (for “squat” Pillars), researchers worldwide agree that the probability of pillar failure and loss of strength decreases. However, the determination of strength of such pillars is still a challenge and needs further research, field trials with a suite of geotechnical instruments and confidence-building measures. As detailed in this paper, stability of mine entries, rather than that of the pillars and assessment of geotechnical problems in right perspectives need sincere consideration. Mitigative measures of geotechnical problems likely to be encountered in an Indian deepmost coal mine is also discussed in this paper. ‘Mass production’ underground technology using continuous miner with stowing is found to be a feasible method for the huge (good grade) coal deposits at higher depth. Chinakuri mine no. I, Eastern Coalfields Limited can become a leader, provided we are able to successfully implement the suggestions as given in this paper at shop-floor level pro-actively