Sonoma Mountain road failure and TDA placement in progress.
The road had been struck by a major landslide in the past, damaging about 600 feet. Engineers built a 20-foot-high corrugated steel wall and supported it with steel H-piles driven into the slope. The project was abandoned in December 2008, following heavy rains, and the affected stretch of the road was finally closed in January 2009.
The official website of the State of California, the project was located on Sonoma Mountain Road in Sonoma County, near Glen Ellen, according to CalRecycle. Sonoma County first selected a retaining-wall solution to repair the damaged roadway, according to online data. A California road repair project took an unusual turn after heavy rains caused a previous reconstruction to fail. Instead of using another traditional retaining-wall system, engineers filled the damaged section with hundreds of thousands of discarded vehicle tires. It was one of two local projects to test using tire-derived aggregate, or TDA, as a practical material to repair landslides and stabilize slopes. The failure was attributed to the poor native soil and excess moisture which left the ground saturated and unstable. But the repair was made in very bad conditions. The failure prompted county officials to rethink how the unstable slope could be repaired with less excavation and lower overall reconstruction costs.
The Sonoma Mountain Road project drew on lessons from an earlier county repair project on Geyser Road where officials had received design assistance for using tire-derived aggregate.