Loose rock is held back by wire netting strengthened by lengthways bars, making up a rollable warping mat for use in underground mining and tunnel engineering. The netting (2) consists of wires formed into spiral units (6-10) and screwed into each other. At a prescribed interval there are spiral units (10) with a central space (11) adapted to the dia. of the lengthways bars (3), for lengthways insertion and guidance of these. There is pref. a sequence comprising four flat units and one with this central space, which can be made by widening the spiral after the netting is made. The spiral units are pref. round. Bars may be ribbed.
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