ABSTRACT
Actively mined coal seams in Illinois are generally associated with weak floor strata whose thickness typically ranges 0.6–2.0m. Research studies over the past five years have conclusively indicated that weak floor strata properties govern design of mine layouts in a large number of Illinois Basin mines. The design problem for a partial extraction mining system requires calculation of stable opening widths including intersections and size of coal pillars to insure stability against coal strength and floor strength failures and differential and absolute pillar settlements. Based on dispersion characteristics of data in statistical analysis, the authors present concepts to develop appropriate safety factors based on reliability concepts developed for structural engineering. They also present regression equations for the estimation of weak floor strata properties from engineering index properties which can be used for the design of coal pillars.
