Reliable assessment of caving behavior of strata and support capacity requirement has been an issue of great demand for reducing the strata control risk while planning of longwall workings specially in difficult to cave strata conditions. This paper describes the findings of an integrated modeling approach for assessment of roof capability and estimation of optimal support capacity for longwall workings in a given geo-mining and strata condition. The modeling approach for support selection is suggested for regular as well as en masse caving conditions integrating the results of numerical modeling and field observation of 23 longwall panels worked in different coalfields of India. A mathematical approach is used to assess the effect of dynamic loading due to en masse caving and to estimate the design requirement of rapid yield valve. The modeling results of a case study of Churcha mine, a mining site well known for its difficult caving strata characteristics in Sonhat coalfield of India is also described.
The economic development of India is being planned to achieve a sustainable growth in pace with some of the fast developing countries of the world. It requires boosting its clean coal production through large scale adoption of high production underground mining technology. Longwall is a globally proven technology to meet this challenge. Unfortunately, majority of workable coal seams in various coalfields of India are overlain by difficult caving strata (Ray 2006). Uncertain strata behaviour in terms of uncontrolled roof caving and face instability coupled with damage of face supports have been witnessed as the major bottleneck in successful implementation of longwall technology in this country. There are numerous examples where improper planning has resulted in wrong site selection and under-rated capacity of supports giving rise to a lot of problems like threats of face instability, frequent face stoppages, irregular face advance, poor face productivity and collapse of workings in the extreme cases. Therefore, developing a reliable approach for assessment of caving behavior of strata and support capacity requirement has been an issue of practical application and great demand for the underground coal mining industry in India. This is essential for reducing the strata control risk while planning of longwall working specially in difficult to cave strata condition. If the problem is predicted by suitable pre-investigation, it can be dealt in a well planned and confident manner.
Although, a number of models and approaches have been developed in different countries for prediction of caving behavior and support requirement, their applicability in Indian geo-mining condition is limited and suffers from considerable error resulting in inconsistent results (Sankar and Singh 1979, Sankar and Dhar 1993, Singh 2004). Experience shows that although the existing approaches offers important contributions towards understanding strata-support interactions, but they do not provide effective means of support specification (Trueman et al 2005). Further, the recent studies conducted by Singh (2007) as well as the Barczak (2006) strongly suggest that bigger the better consideration of support selection is not a good practice in support selection for ground control.