Confusion Hill/Highway 101, Mendocino County

Tire-Derived Aggregate as Landslide Remediation/Slope Stabilization

Construction site with TDA wrapped in geotextile fabric prior to soil placement

TDA wrapped in geotextile fabric prior to soil placement.

In 2009 the California Department of Transportation (Caltrans) completed the lightweight fill project located at Confusion Hill on U.S. 101 near Piercy in Mendocino County. The project used tire-derived aggregate (TDA) for this rockslide/road repair project.

The rockslides have been occurring for thousands of years and have been impacting the highway for the last 17 years with roadway slip-outs occurring more frequently in recent years. The size of this rockslide is approximately 3,000 feet wide and 1,100 feet high.

Frequent road closures due to falling debris and slope movement were a constant maintenance problem. In 2001 there were $3.2 million in roadway stabilization costs. The purpose of this project was to provide a reliable route at the Confusion Hill slide area and keep U.S. 101 open to vehicular traffic.

Construction site showing the final TDA placement on roadway

Final TDA placement.

The new route bypasses the rockslide area through the use of two new bridges. The north bridge embankment had an existing underground drainage structure which, it was determined, could not handle any additional load which would result from the added height of the north bridge embankment.

To prevent possible damage to the subsurface structure, a lightweight fill material was needed. TDA was chosen as the fill material for the project because of its light weight and cost-effectiveness. The existing fill material over the structures was removed and replaced with the lightweight TDA material. The project used approximately 270,000 waste tires and was completed in 2009.