A federal agency made a rock cut during the road construction for its headquarters office access road in the early 1970’s. Although the road cut is nearly continuous in this area, episodic rock failures have occurred since its construction. GeoStabilization International® was asked to stabilize the failing rock slope.
The rock cut slope consisted of 980-linear feet of near vertical weathered schist and sandstone, of which some wedges have failed and blocked the roadway below. The rock cut was broken into a lower and upper section. The lower section ran the entire 980-linear feet and the upper section ran another 280-linear feet. A v-ditch lined bench separated the upper and lower section. Average height of the sections was 35 feet. The total estimated area of both sections was 45,000 square feet.
The exposed rock was systematically jointed and had very blocky characteristics. In general the rock blocks were little to moderately weathered, strong to very strong, and moderately hard to very hard. Weathering in the rock mass was concentrated along discontinuity planes, where the rock was generally highly weathered to locally completely decomposed.
A team consisting of GeoStabilization, a general contractor, and a consulting engineering firm conducted mechanical scaling consisting of a combination of a long reach and traditional excavators with scaling blanket attachments. Following the mechanical scaling process,
GeoStabilization’s rockfall technicians hand scaled the slope to insure removal of any remaining loose rock material. GeoStabilization’s rockfall engineers redesigned the planned 14-foot long spin-lock anchors solution in favor of 24-ft long post-tensioned SuperBolts™, which, due to their speedy installation, were installed at the same cost and in less time than the planned spin-lock anchors. The SuperBolts™ were installed throughout the rock face and used to anchor Maccaferri® B600 high strength steel rockfall mesh. The project was completed safely, on time, within budget, and at a higher factor of safety than the original design.
Swinging Bridge Anchors, Virginia Department of Transportation