ABSTRACT
Pillars in stratified ground are routinely formed between entries and crosscuts during development of main entries, sub-main entries, and panel entries. A simple explanation of the data fit embodied in the size effects strength formula illustrates the point. When cubes of different sizes are used to examine size effects, end and shape effect explanations do not account for a decrease of strength with size. The first is that any strength enhancing confinement associated with end friction is ignored. A detailed analysis of pillar stress in dipping strata shows that to close approximation, gravity forces that an overburden block exerts on a pillar before excavation are the same as the forces after mining, as was the case for pillars in flat seams. Joint failure mechanisms and strength failure of a pillar therefore need to be examined for pillar design. Multiseam mining involves simultaneous or sequential excavation in two or more seams. Large sedimentary basins typically contain a repeating stratigraphic sequence.
