Coastal Bluff Stabilization with Soil Nailing

Following the rainy season in northern California, a county suffered significant erosion and needed bluff stabilization along a highway hugging the coastline. To avoid specific regulatory permits and to complete the slope stabilization at a lower cost, the county selected GeoStabilization International®, experts in soil nail wall technology, to provide a soil nailing repair to ensure the site would not require future landslide mitigation.

The roadway presented a multitude of challenges at two locations for the county’s engineer, where shallow landslides along the oceanfront drive were combined with coastal erosion, restricting regulations, archeological concerns, and corrosive ocean spray. At the first location, a 150 linear-foot section of the 36-foot-high bluff adjacent to the roadway had failed, leaving an over-steepened head scarp that threatened the stability of the highway above. The second location consisted of six to eight feet of stiff, high plasticity clay overlying a siltstone cliff. When the clay above was subjected to surface erosion, it subsequently exposed the top of the siltstone cliff below. As the freshly bare siltstone was uncapped, it became exposed to erosion and would regress at the same rate as the clay above. This cycle repeated itself until the cliff eroded to the roadway’s edge, requiring landslide mitigation.

Bluff Stabilization

Historically, the county would place large-diameter boulders over the side of the bluff to prevent surface erosion and retard slope instability. However, local environmental groups and the California Coastal Commission no longer allow rock revetments as a repair. Furthermore, there was concern about disturbing a sacred Native American burial ground at the first location. Any drilling about 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.

Soil Nailing Solution

GeoStabilization’s engineering group’s repair plan, which was accepted by the county, consisted of an engineered soil repair comprised of a soil nail wall constructed using corrosion-resistant launched fiberglass SuperNails® for soil anchors, combined with sculpted shotcrete facing to halt surface erosion. First, using the Soil Nail Launcher™, the fiberglass soil nails were launched horizontally into the slope in the design’s specified pattern before the SuperNail® part was added. The crew then applied a layer of steel-reinforced shotcrete before a finishing shotcrete layer was sculpted and stained to match the local geology. This solution was installed without entering the tidal zone, thus reducing the need for specific regulatory permits. An archeologist was not required because launched SuperNails® do not displace any soil material when “shot” into the slope.

This solution was the least expensive of all options considered and remains intact after later being hit by two Pacific tsunamis. Contact GeoStabilization International® at 855-579-0536 to learn how our teams are mitigating landslides and providing residential slope stabilization, slope monitoring, slope protection, and landslide prevention services.