Rock bolts and wire-ropes are in extensive use for ground support in mines, tunnels and other excavations. A simple and economical method of support using scrap wire ropes, conceptually similar to a roof truss, was evolved in 1974 for use in Indian coal mines. The technique, (rope or truss), has since found wide application in coal mines in India for support of the roof and sides of roadways. The method comprises essentially the following: two holes are drilled in the roof on either side of the roadway at an inclination of 45 deg and to a depth of 1.8 M. Using a sand-cement mortar, two ends of a rope are grouted in the holes. After the grout has set, timber laggings are used to tighten the rope against the roof. For roadway spans exceeding 3.6 M, full-column grouted bolts (with an eye-hook at the bottom) are used for additional reinforcement at mid-span. The rope is passed through the eye-hook and the ends grouted over the rib line on either side. The support system has been tried out on an experimental basis over the past 6 yr in some 60 coal mines and proved to be economical and effective vis-a-vis conventional roadway support systems. From a model study to evaluate the relative reinforcement actions with bolting and wire-rope systems it was concluded that: (1) The reinforcement increased by 17% with side bolts inclined at 60 deg and extending over the support ends vis-a-vis the vertical bolt system. (2) A steel strap interconnecting the bolts was found to act as a tension member offering resistance to the movement of the bottom layer. (3) Wire rope stitching as a system proved to be more effective than the other bolting systems examined. (TRRL)
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Jun 1, 1985
U Grotowsky + 1