How to eliminate roof and floor failures with yield pillars

This, the first part of a two-part article, describes a new ground control method which substitutes ground self-support for artificial support, even in very weak ground, by utilising excavation geometry to redistribute stresses. The method has been used successfully in potash and other mines, but the case considered in this paper is its first known application in coal mining. The history of severe floor heave in an Alabama mine is traced and the failure of conventional methods to alleviate the problem is indicated. The formation of yield pillars, designed to fail in a controlled manner, redistributing stress in an advantageous way, is described. Test results showed the ability of the yield pillar/stress control method to control floor heave problems associated with soft floor conditions.