Trait of subsidence under high rate of coal extraction by longwall mining: some inferences

Transformation in surface topography is a common phenomenon caused due to underground mining. With a view to focus outward, underground mining at a depth of 410 m although earlier considered as mothball is indispensable as on date to meet the production target. Subsidence investigation has been carried out over longwal panel no. 1 in Adriyala mine of Singareni Collieries Company Limited (SCCL) located in Godavari Valley Coalfield. The rate of face advance varied between 2.7 and 4.8 m/day. The present study envelops cementing relation of subsidence due to underground mining by longwall method with the active and old dumps, partially covered over the panel. Symmetric subsidence profile has been observed across the panel with higher angle of draw in dip side. Resettlement of dump led to higher vertical displacement and found to be an indispensable investigation for stability viewpoint. The angle of draw has been analyzed to be a controlling parameter with respect to the rate of face advance. The impact of subsidence on surface has been evaluated by constructing walls at maximum possible tensile zones and development of cracks after subsidence has been observed. Hydrogeological study has also been conducted, from seepage viewpoint, to evaluate the extent of damage in the strata for safe underground working. The investigation has been conducted during and after mining, with and without release of canal water, to assess the influence of seepage in ground. The assorted subsidence and hydrogeological investigations can be applied to interpret the extent of damage and for comprehensive understanding of the trait of cracks on the surface, in the strata and their continuity thereof.