In India most of the coal mines are developed by bord and pillar method. In many of the mines the extraction of pillars are being restricted due to its surface constraints. A considerable amount coal is left in pillars due to this reason. This paper deals with the application of numerical modeling for optimum percentage of extraction of coal, keeping in view of the long term stability of the partially extracted pillars, where the horizontal stresses are predominant. In this paper a case study of running mine has also been made by 3D numerical modeling method to asses the most suitable partial extraction method.

1. Introduction

Bord and pillar method of mining is widely used in India for extraction of coal from underground. The design of coal pillars is mainly guided by the Coal Mines Regulation (CMR)-1957, which is considered only the depth factor. Whereas, in the practical field the design of pillar is guided by two conflicting factors such as in one hand it should be as small as in cross section so that maximum extraction can be possible and in the other hand it should be bigger in size for its stability. The design factor is further guided by depth, geological disturbances and type of strata etc. In many of the underground mines in India, a considerable amount of coal is being blocked in coal pillars due to structures and import surface features.

Moreover, due to flat gradient and scarcity of sand, the extraction of these pillars with stowing becomes difficult. This blocked coal can be extracted by using partial extraction method to its maximum percentage with the help of numerical modeling technique due regards to its long term stability. FOS of small pillar (Split pillar) is considered greater than 1.5 for long termstability. Like others, the design procedure of coal pillars also depends upon its stress-strength ratio, i.e. the load on pillar to the strength of the coal pillar. Different scientists of the different countries developed empirical relations for estimation of strength of coal pillars and probable stresses, which will generate on the pillars for a certain set of geo-mining conditions prevails there. Thus the empirical relations developed for a particular set of geo-mining conditions will not be precisely applicable to another set of conditions existing in other countries; here lies the importance of numerical modeling method. Stability of pillars of any type of partial extraction can be assessed with the precise input of physico-mechanical properties of rock and coal, and geo-mining conditions. This paper deals with the various split options including wide stall method to judge the long termstability of pillars where the horizontal stresses are predominant.

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