Field and numerical modelling on the stability of underground strata in longwall workings

Abstract

The longwall method is one of the feasible and efficient underground mining methods for greater depth of workings. Recently, Singareni Collieries Company Limited (SCCL), the largest coal-producing government company in the Southern part of India, has deployed a high capacity (2 × 1152T capacity) power support system in its Adriyala Longwall Project (ALP) at a depth of 375 m. There was a concern about the stability of the longwall workings and the protective pillars. Thus, research work was carried out with the geotechnical instruments and numerical modelling tools to analyze the stability while retreating the longwall panels. The outcomes revealed that the convergence in the gate roads increased with the longwall face advancement and the area of exposure. The pressure of the powered support legs on the dip side was less than the rise side legs, which implies a stable roof condition over the longwall face. An abutment zone was identified ahead of the line of extraction up to 10–25 m and presumed from the Factor of Safety (FoS) criterion that within this zone, the longwall pillar possibly will be of better stability at every stage of extraction. The results obtained from this study would be helpful for the mining engineers to understand the behaviour of underground strata in longwall workings.