Assessment of Caving Behaviour of Strata and Powered Support Requirement for Safe Longwall Extraction Under Difficult Caving Strata Condition

A reliable assessment of progressive caving behaviour and rational support capacity requirement is essential for minimising the risk of planning and sustainable execution of productive longwall operation.

Successful implementation of such highly inflexible operation under unfavourable and challenging strata conditions requires a dedicated approach for proper evaluation of impending issues and their practically feasible solution. This paper presents the results of a numerical modelling based study for assessment of progressive caving behaviour and associated repercussion on strata control requirements in a longwall mining under difficult caving strata condition in presence of dolerite sill formation. The results obtained from numerical modelling have been used to assess the caving mechanism and delineation of dynamic loading potential due to en masse caving of strata. Further study has been done to assess the effect of softening of strata on the likely improvement in caving characteristics of strata and potential relief in severity of dynamic loading during progressive face advance. Further, the results of parametric modelling using different support capacities have been validated with the design function of powered roof supports to assess the rational support requirement for safer longwall working in the given geo-mining condition.

The study reveals that the coal seam was not suitable for longwall working under in situ strata condition.

The study also concludes that powered supports of 4 x 800 t capacity fitted with rapid yield valve having peak discharge rate of 1934 litre per minute can be a rational design for safe longwall operation provided the strata within the active caving zone is softened by 40% in such strata condition.