Abstract: Apparatus for determining compressive stress in an in-situ roof support pillar may comprise a convergence meter positioned in one of the two entries for measuring the total entry convergence, i.e., roof sag and floor heave, and for generating an output signal related thereto. A computer system connected to the convergence meter is responsive to the output signal and calculates the compressive stress in the pillar based on the total entry convergence and based on whether the pillar is being subjected to at least one of a number of load types including a first front abutment load, a second front abutment load, and a side abutment load.

Abstract: A continuous mining linear advance system comprises a dual action drum cutter for removing coal from a face of the entry. The dual action drum cutter removes the coal from the face by shearing across the face in a direction transverse to the direction of advance and by cutting directly into the face in the direction of the advance. A conveyor system operatively associated with the dual action drum cutter carries away coal removed from the face of the entry in a continuous, non-interrupted manner. A number of self advancing roof supports positioned adjacent the dual action drum cutter support the roof in the immediate vicinity of the face. Roof bolting devices positioned behind the self advancing roof supports install roof bolts, and a pillar casting system positioned behind the roof bolting devices constructs a series of pillars which provide long term roof support.