Abstract: A bi-directional shearing machine mines a longwall face at the bottom of a thick mineral seam in a retreat operation under the protection of a row of adjacent powered roof supports each of which extends in a direction transverse to the solid face. Progressive advance of these roof supports allows the overlying mineral strata to cave. Each roof support is separated into articulated forward and aft units provided with separate sets of hydraulic props and having their solid canopies interfitted in end-to-end relation. The bases of the two units are interconnected with a push-pull hydraulic ram which enables relative longitudinal movement between the two units so that they may be advanced independently along a common axis toward the solid longwall face as the work progresses. During the advance of the forward units to provide face support, plowing and loading of caved mineral on the gob side may proceed without interruption.

Abstract: In the mining of a thick underground mineral seam, parallel submain entries are developed at the top of the seam or at an upper level where a competent roof exists. Spaced apart parallel sets of panel entries are driven at right angles to these submain entries along a downwardly sloping path to the bottom of the seam. The entries are continued coincident with the bottom of the seam to any desired point at which their extremities are connected with bleeder entries so as to define a series of longwall panels. These panels are mined in retreat under the protection of advancing roof support structures so as to induce caving of overlying strata.

Abstract: In a longwall mining system, a work face extends between parallel sets of multiple head- and tailgate entries, adjacent entries of each set being separated by rows of chain pillars. Lengths of a headgate entry immediately adjacent the longwall panel and the pillar breakthroughs to the next headgate entry are progressively pump packed in advance of the longwall face with a coherent thixotropic roof supporting material. As the longwall face is mined, a bidirectional shearing machine cuts through the roof supporting material and the chain pillars, which are then removed in a continuous operation.