UNSTABLE ROCK AND ITS TREATMENT SNOWY MOUNTAINS SCHEME
Treatment:
- Wire surface anchors were embedded in clayey material and a layer of mortar 1 to 2 in. thick applied pnuematically.
- 17 gauge mesh attached, and long wires attached to this mesh to anchor later mesh.
- The slot was filled with pneumatically applied mortar until flush with the wall.
- 8 gauge mesh in a strip 6 ft wide was attached by rock bolts, rock anchors, surface anchors, and by wires previously attached to the 17 gauge mesh.
- The entire zone was covered with pneumatically applied mortar to a thickness of 1 to 3 in., with a minimum of 1 in. cover over the mesh.
Fig. 16.—Jointed granite, with narrow crushed seams and areas of decomposition. Supported by grouted rock bolts during excavation. Heavy wire mesh pinned by rock bolts, rock anchors and surfaces anchors in preparation for application of pneumatically applied mortar.
All seams of this kind thicker than about ½ in. are treated with pneumatically applied mortar to prevent their erosion. Isolated seams a few inches thick are cut hack to a depth at least equal to their width and backfilled with pneumatically applied mortar. For wider seams the mortar is reinforced with wire mesh.
Light wire mesh was used in seams of moderate width intersecting sound rock which did not require support where protection of the seam against erosion was the only requirement. Heavy mesh was used over seams wider than a foot or so, and where the adjacent rock was closely jointed and required support. Recently the trend in practice has been to use heavy mesh exclusively.
Disintegrating basalt dykes are treated with mortar reinforced with heavy mesh and supported by rock bolts (Fig. 17).
Fig. 17.—Treatment of a disintegrating basalt dyke 1 to 2 ft wide with sheared walls
Broad patches of partially decomposed granite which could disintegrate in water occur both as individual features and in association with sheared zones. These are treated with reinforced pneumatically applied mortar tied to grouted rock bolts.
Broad areas of closely jointed hard strong rock with a tendency to ravel may be treated with plain pneumatically applied mortar.
