Strata behaviour of a wide and deep longwall panel under massive sandstone bed - a case study

摘要

Longwall technology is one of the principal underground coal mining methods widely used around the globe which is not fully emerged in India. However, since the introduction of first self-advancing powered roof supports, there has been mixed experience of longwall technology. History of failure of some longwall panels desponded the success stories of others. Majority of longwall downtimes and/or failure had been attributed due to poor capability of roof, inadequate capacity of supports, lack of knowledge on longwall caving mechanisms, less than adequate strata monitoring systems, etc.Strata around coal seams in India are dominated by competent beds, which do not normally cave in immediately after face advance, rather it remains in hanging condition for certain length and break into large discrete blocks. This type of caving mechanics is irregular and complex. Fracturing of competent bed in the immediate roof zone is certain to manifest itself on face as heavy load on supports, bleeding of hydraulic legs of supports, aggressive face spall and guttering in gate roads and in worst conditions longwall face stoppage and sometimes even structural failure of supports as the severity may be.This paper presents a case study of strata behavioural experiences gained while extracting a deep and wide longwall panel overlain by 3.0 to 3.5m coal roof as immediate roof and 20 to 28m thick competent sandstone bed as main roof with high capacity longwall equipment. While extracting the panel the precise strata monitoring and trigger action response plans are prepared and implemented successfully for negotiating all the strata control hindrances.