Assessment of mining induced stress development over coal pillars during depillaring

Earlier, an analysis of in situ observations at different sites of Indian coalfields was made to visualize the development of mining induced stress over the coal pillars facing goaf line. An empirical relationship was also attempted to estimate the range of influence and the value of ultimate induced stress (vertical) over the coal pillars. However, the attempt was based on field monitoring data of only five depillaring faces with varying geo-mining conditions. Considering a need of the Indian coal mining industry, further field monitoring is done at 16 more depillaring faces with depth cover (average) range variation from 44 to 244 m. The geo-mechanical properties of overlying roof strata of each site were also determined to assess their caving characteristics in terms CMRI (now, CIMFR) caveability index, which nearly varied from 1000 to 10,000 for the studied sites. Presenting a brief review of different studies conducted for mining induced stress development, this paper discusses outcomes of the in situ studies of mining induced stress development during depillaring under varying geo-mining conditions. Considering the results of this study, earlier developed empirical relationship was, accordingly, modified for estimation of the range of influence and the value of ultimate mining induced stress (vertical) over the coal pillars. (C) 2011 Elsevier Ltd. All rights reserved.