Some consequences of the hinged-block hypothesis

Summary

• 1. A promising model of a rock layer underworked by a longwall face is that of a stratified medium with reduced cohesion or without cohesion between strata. The simplest such medium is a regularly stratified medium, and with this we must begin the study of the behavior of underworked rock.

• 2. When such a medium is underworked, periodic fractures of the strata arise, with movement of blocks in the form of “multistory” systems of different mechanisms, formed for the underlying supports, caved rock, and stowing of the support zone. The width of the latter may vary with the circumstances, is often much greater than that held up by the supports in the face area, and extends to various heights into the immediate and main roofs.

• 3. By using methods of the theory of mechanisms and structural mechanics, we can derive simple formulas for the main parameters of interaction between the supports and other load-bearing structures with the roof rocks, according to the type and parameters of the mechanisms forming in the support zone, which in turn depend on the structure and support conditions of the roof. These formulas can serve for a quite wide spectrum of support zones, formed in model stratified media, and, according to the validity of the hinged-block hypothesis adopted, under pit conditions, in roofs above longwall faces.

• 4. The most important problems in research on rock pressure phenomena in longwall faces in level seams remain the determination under natural conditions of the actual varieties of mechanisms formed in the support zone, and their main characteristics in relation to the geological and mining conditions of their origin.