Analysis of pillar punching into soft claystone in southern Illinois

Subsidence can be caused by mine level failures in the roof, pillars or floor which allow displacements that propagate to the surface. However, in Illinois, plastic failure of weak claystone floor dominates the failure process. The objective of the research by the Bureau of Mines is to define the failure mechanisms and resultant upper bounds to the limit loads given by the limit analysis method for both square and rectangular pillars punching into plastically behaving floor of both finite and infinite thickness. This paper describes the assumptions, techniques and preliminary results of a laboratory program designed to define the three–dimensional failure mechanisms in an infinitely thick, frictionless, perfectly–plastic material beneath a square punch.