Advancing pit prop and mine roof covering system - uses lubricated zigzag folded plastics sheets, successively overlapped to guard against roof falls

An advancing pit prop system includes application of plastics, sheets to the roof as a protection against falls during operation. These sheets may be of polyethylene, and are folded in a zig-zag manner to form a bundle between 0.6 and 1 m thick. Each sheet is inserted between the top parts of the pit props so that it is overlapped with the free edge of a previously applied sheet. The pit props are then advanced, trapping the sheet, so that it is held in position. Lubricant can be applied between the sheets. Their thickness can be between 0.2 and 0.5 mm, their tear resistance is at least 15N/mm2 and elongation at least 4m/m or 400%. Alternatively, instead of a single sheet, two or three sheets, each 0.075 to 0.3 mm may be used on top of each other. A hygroscopic salt layer can be retained by the sheet.