Room-and-Pillar Design Practices of Illinois Coal (No 5) Seam

Abstract

Economic development as well as realisation of the basic human needs is becoming increasingly dependent on the availability of modern energy availability. Fossil fuel based energy still remains the major source for sustaining and improving standard of life though there are strong strides made by other sources as hydro, nuclear, gas, oil, etc. One estimate put the proven coal reserve in the state of Illinois to be at least 30 billion tones, another puts it 80 billion tones. Coal production from the mines in Illinois contributed about 61.7 million tons in 1990. In mines pillars are left to perform a variety of functions which influence their size and disposition. Room and pillar method of coal mining constitute the major mechanism of coal extraction in most parts of the world. Wilson’s approach divides the pillar into two zones and approximate rules were prescribed for stresses in the two zones. Partial extraction of coal through room-and-pillar mining mechanism plays a major role in Springfield coal seam (No. 5) in Illinois, USA too. The coal beds are typically flat tabular deposits. Until mid 1980s coal mining layouts were designed based on experience and procedures developed primarily for Appalachian region. In this paper an analysis of pillar design practices adopted in five mines operating in the Illinois coal seam has been made. There were no comprehensive design procedures available for mines in Illinois Springfield (No. 5) coal seam. So a detailed investigation was carried out to evaluate the failed and stable pillar data to assess the appropriate safety factor(s) for design as well as to analyse the applicability of the Wilson’s approach in the No. 5 coal seam. Pertinent data were collected from permit application and field visits. The paper presents the geology of the Illinois coal seam, a discussion on different pillar design equations available, analyses of the safety factors of both stable and unstable pillars, etc. A common design equation had also been developed for the mines operating in these two seams.