Abstract: Methods for pillar recovery in chamber-and-pillar working materials in underground stratified beds are disclosed. Additionally, tubbing units for pillar recovery in chamber-and-pillar working of materials in underground stratified beds are disclosed. An extraction device is aligned obliquely to pillar galleries located between the pillars and the roof is supported in front of the retreat face of the extraction device with a plurality of tubbing units, each tubbing unit being adjustable in height and width and movable through operation of a vehicle. The tubbing units may be moved through other tubbing units that are set, and reset in another position.

Abstract: A mine prop is comprised of an elongate tube having a slenderness ratio that would generally allow buckling or kneeling of the elongate tube when exposed to a sufficient axial force. A plurality of elongate support members having a length less than the elongate tube are attached to the tube to prevent buckling or kneeling of the elongate tube along the portion of the tube to which the elongate support members are attached. The portions of the tube that are unsupported by the elongate support members define one or more yieldable zones proximate at least one end of the tube. A compressible filler material is disposed within at least portion of the tube to support yielding in the yieldable zone.

Abstract: The roof of a heading cut by a continuous mining machine is supported by cantilevered roof beams forming part of a shield. There are at least two sets of roof beams which can be raised and lowered separately by means of hydraulic rams. When one set is lowered and the other set is raised, the lowered set can be pushed forward against the raised set by means of hydraulic rams. The cantilevered roof beams extend far enough forward to support the roof over the driving position of the continuous mining machine. The width of the shield should be less than the width of the mining machine, so that the shield can advance along the heading cut by the mining machine. Furthermore, the shield includes a conveyor for conveying the mined material from the mining machine backwards to a shuttle car or other conveying system.