Document Type

Conference Paper

Publication Date


Publication Details

R. Seedsman, The strength of the pillar-floor system, 12th Coal Operators' Conference, University of Wollongong & the Australasian Institute of Mining and Metallurgy, 2012, 23-30.


The strength of the roof/pillar/floor system is controlled by the component with the lowest strength. In some coal seams the floor can be the weakest component and in these situations bearing capacity concepts drawn from foundation engineering can be applied. The low strength floors tend to be clay-rich and can be analysed as behaving in an undrained state (effective friction angle equals zero). A simple thin-layer bearing capacity equation has been found to correctly identify problematic low strength floors. The input variables are the unconfined compressive strength of the layer, its thickness, and the width of the pillar. All reported pillar collapses should be checked against this simple relationship and removed from the pillar collapse database if floor failure is indicated.