Geotechnical Challenges and Failure Mechanisms in Indian Underground Coal Mines: Roof Stability, Pillar Design and Floor Behaviour under Complex Geological Conditions

Abstract

Underground coal mining in India is constrained by complex Gondwana geology, variable rock-mass quality, increasing extraction depths, and heterogeneous stress conditions. Weak laminated shale, jointed sandstone, high horizontal stresses, pillar degradation, floor instability, and mining-induced deformation frequently interact during underground extraction. This paper synthesizes the geotechnical evidence presented in the source report, focusing on roof and rib stability, pillar behaviour, floor response, stress redistribution, and associated failure mechanisms. Major Indian coalfields including Jharia, Raniganj, Singrauli, Talcher, Wardha Valley, and Godavari Valley are considered within the broader geological framework. Representative coal-measure rocks commonly exhibit fair-to-poor rock-mass quality, with RMR values generally ranging from 35 to 60. The reported high horizontal-to-vertical stress ratio of 1.5–3.0 at greater depths changes the dominant failure response from gravity-controlled instability toward stress-driven deformation. Field observations indicate roof convergence of 0.5–5 mm/day during development, increasing during depillaring. Numerical analyses demonstrate substantial reductions in roof sag and plastic-zone development following systematic reinforcement. Case studies from Jharia and Singrauli illustrate how delamination, wedge failure, rib spalling, interface shearing, moisture weakening, and abutment loading can combine into progressive instability. The synthesis indicates that site-specific characterization, calibrated numerical modelling, appropriate pillar dimensions, reinforcement, extraction sequencing, and continuous monitoring are necessary for reliable ground control under Indian conditions.