Difficult geo-mining conditions of a deep seated coal pillars limit the scope of conventional semi-mechanised depillaring process, mainly due to their slow rate of extraction. Application of a fully mechanized depillaring process has resulted faster rate of extraction resulting improvement in safety along with production and productivity of the depillaring faces. Out of six mechanized depillaring practices in India, the three successful ones of Anjan Hill, Jhanjra and Pinoura Mines do not belong to deep cover (<200m). While the Tandsi depillaring is practiced at nearly 260m depth of cover and achieved intermediate results.
The deepest practiced mechanised depillaring panel in the county is CMP-1of VK7 at 377m of cover. This depillaring encountered massive collapse (before main fall), which adversely affected the pace of mechanisation for pillar extraction operation at higher depth in the country. Actual cause of the problem is still being investigated and is found difficult to be concluded. However, as per core analysis results, a good understanding of the nature of overlying strata might have guided the approach for a better pattern of the pillar extraction and the chance of failure might have been arrested. After realizing this fact, a depillaring operation in the neighboring panel 26 of the mine was successfully conducted. Here, the menace of dynamic loading due to competent overlying strata could successfully be encountered through management of the natural support only.
The sixth mechanised depillaring face is successfully being practiced at GDK 11 Incline at around 310m of cover. Again, here application of available knowledge of the site conditions helped in successful completion of mechanised depillaring operation in couple of panels. Field investigations through underground instrumentation and monitoring showed distinct natures and amount of stress re-distribution for shallow and deep cover of the depillaring. The prominence of periodic nature of face loading at shallow cover got reduced during depillaring of a deep coal seam. Pillars around extraction line encountered, almost, continuous loading after first major fall during pillar extraction from deep seated coal seams.
