Indian coalfields inherit difficult geo-mining conditions, which make it difficult to extract developed coal pillars by an underground mining approach. However, to meet the demand of coal production, three attempts of application of the mechanised depillaring have been made with mixed results. This paper, first, briefly presents results of the country's first fully mechanised depillaring face and, also, discusses the outcomes of two other attempts of mechanised depillaring. A brief review of the exiting geo-mining conditions Indian coal-fields shows that the role of support, both, natural and applied support is an important issue, which need to be addressed for the varying conditions of different sites. The important technical point to notice during the first fully mechanised depillaring face is successful application of high capacity, pre-tensioned, stiff and resin grouted roof bolts as systematic support of roof (SSR) and breaker line support for the laminated roof of the site. A review of different mechanised depillaring faces shows that the high capacity roof bolts and mobile roof support are complementary for weak and moderate roof strata. But, this approach of roof support may not always be applicable in India due to frequent encounter of massive roof strata. It is an open fact that pillar recovery at higher depth cover is another important emerging issue in the country. Coal mining activity at deeper cover is likely to intensify in the future because the shallower deposits are exhausting. At greater depths, the size of pillars is too wide to be fully extracted with single pass pillar stripping techniques. Here pillar splitting before extraction becomes the only alternative if the pillars are to be fully extracted. On the basis of experiences of different conventional semi-mechanised depillaring faces, this paper also discusses the rock mechanics aspect of manner of pillar extraction and efficacy of the left out fender for a successful high speed depillaring. It is realised that the experience of local rock mass behaviour is an important input for a successful adoption this mass production technology.
Future extraction of coal, mainly through underground mining, is going to encounter, relatively, deeper excavations in difficult rock mass conditions. In India, large number of coal seams has extensively been developed by formation of pillars to meet the increasing demand of coal in the country. This is found to be a simple and safe method of coal production from underground mines. The process of pillar formation also received favourable situation due to presence of the competent coal seam and similar surrounding rock mass. Indian Coal Mines Regulations (CMR), 1957 is also quite liberal for pillar formation. This strategy of coal production found suitable for the Indian coal mining industry because of low capital investment and involvement of trivial technical expertise. Now, industry is looking towards the huge amount of coal locked up in the pillars. Underground coal mining in India is facing serious techno-economical challenge during depillaring of the developed coal seams. Conventional depillaring frequently encounters strata control problem and the productivity remains quite low.
