Following the rainy season, a County in far northern California suffered significant coastal bluff erosion. To avoid certain regulatory permits and complete the stabilization at a lower cost, the county selected GeoStabilization International®’s launched soil nails and sculpted shotcrete as the mitigation technique. One particular roadway presented a multitude of challenges at two locations to the County Engineer where shallow landslides along the oceanfront drive were coupled with coastal erosion, confining regulations, archeological concerns, and corrosive ocean spray.
One particular roadway presented a multitude of challenges at two locations to the County Engineer where shallow landslides along the oceanfront drive were coupled with coastal erosion, confining regulations, archeological concerns, and corrosive ocean spray. The
first location fell victim to northern California’s heavy winter rains. A 150 Linear-Foot section of the 36-foot high bluff adjacent to the roadway had failed, leaving an over-steep head scarp. That scarp threatened the stability of roadway above.
The second consisted of six to eight feet of stiff, high plasticity clay overlying a siltstone cliff. The clay above fell subject to surface erosion and subsequently exposed the top of the siltstone cliff below. The freshly exposed siltstone, un-capped, was then subjected to erosion and would regress at about the same rate as the clay above. This cycle repeated itself to the edge of the roadway.
Historically, the county would place large diameter boulders over the side of the bluff to prevent surface erosion and improve slope stability. However, local environmental groups and the California Coastal Commission no longer allow rock revetments for those types of repairs. Furthermore, at the north location, there was concern about disturbing a sacred Native American burial ground. Any drilling in or around the burial ground was strictly prohibited unless it was monitored by an archeologist familiar with the history in that area, adding costly fees to the project.
GeoStabilization International® was contracted to install corrosion-resistant Launched fiberglass SuperNails® to stabilize the bluff and to face the bluff with shotcrete to halt surface erosion. The shotcrete was sculpted and stained to match the local geology. This solution was conducted without entering the tidal zone, thus reducing the need for certain regulatory permits. An archeologist was not required because Launched SuperNails® do not displace any soil material from the stabilization area. Also, Launched fiberglass SuperNails® with a sculpted shotcrete facing presented the least expensive of the potential solutions.
This repair remains intact after later being hit with two Pacific tsunamis.
A major roadway in California’s Bay Area presented a multitude of challenges to the state’s Department of Transportation where a large 140-linear foot portion of bluff supporting the roadway was simply sliding out to sea.