Evaluation of Current Pillar Design Practice in Ramagundam Coal Belt

Abstract

Bord and Pillar mining is the oldest and most popular mining method to extract coal from underground. It is simple, easy to operate and reasonably safe. The pillars form the natural support to the overburden roof and transfer the load to floor. In the process a large portion of the coal remain blocked for long period till depillaring is carried out. The underground coal mines in India predominantly follow the Bord and Pillar method of extraction. The stability of the roof and floor depends on the stability of the pillar. The pillar stability depends on its strength, nature of coal, presence of discontinuity, method of extraction, etc. In India DGMS guidelines govern the design of pillars whereas in other parts of world the pillar design is based on strength calculation of coal and other factors. Some of the approaches are given by Bieniawski, CIMFR, Obert – Duvall, Jaiswal – Shrivastava etc. In this investigation an attempt has been made to investigate the current pillar design practice in one major coal belt of India vis-à-vis other approaches. The investigation was considered in terms of extraction percentage and safety factor for each design approaches. Pillar dimension has been optimised to determine the extraction ratio of a stable safety factor. 35 m square pillar was found to be stable with more than 2 % enhanced recovery at a depth of 270 m in comparison to the existing practice.