Abstract

High economic benefits and a good infrastructure network have been pushing ongoing coal projects near the southern border of Mongolia for a long time. To continue the consistent run of the coal export and to make good returns, the transition from open-pit to underground has to be considered further due to the economic pit limit is reached with mining depth increases when the stripping ratio is relatively high to a point where it is no longer feasible to continue mining.

Under those circumstances, the underground mine will be set up right below the inactive existing open-pit or end-wall slope. To provide a safe and long-term stable output of the underground coal mining in the transition area as well as to study the failure mechanism which consists of slope instability and surface subsidence, and the uncertainties associated with several strata conditions at mining design stages ahead of the project commences, crown pillar stability and appropriate dimensions have been studied in this paper based on results of numerical analysis. Numerical simulation has been carried out by Phase2 two-dimensional FEM analysis and this research mainly considered studying the influences of different geological conditions of coal measure; coal seam thickness and dip angle.

Introduction

The coal mining industry is significantly affecting the economic development in Mongolia for the last two decades since coal export to China started in 2004. Almost 99 % of total coal mines are surface mining, and the remaining 1 % is a small-scale underground mine that is nearly closed due to financial difficulties.

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