Critical Evaluation of the Current Design of Coal Room and Pillar Panels as Input for Changes to the Future Design Methodology

The design of coal room and pillar panels has traditionally focused primarily on pillar behaviour. However, if the design process were approached from first principles, one would start with the design of the rooms and first look at the redistribution of the stresses around the rooms. Numerical simulations (elastic and elasto-plastic behaviour) clearly demonstrate the development of relaxed zones in both the roof and floor strata, as well as along the sidewalls in the pillars. The extent of these relaxed zones is governed by factors such as excavation geometry and the ratio of vertical-to-horizontal in situ stresses. A second concern is the widespread tendency to approximate in situ pillar behaviour through vertically loading experiments, such as uniaxial compression tests. These experiments would only be representative if pillars were constructed structures. More complex stress paths develop within the coal pillars during mining, and the load is far from uniform. The current design practices are based on the average pillar load, while the rock behaviour is not determined by average stresses but by local stresses. This paper concludes by proposing directions for future research and by identifying opportunities to improve current understanding and design methodologies for coal room and pillar workings.