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. According to CalRecycle, the official website of the State of California, the project was located on Sonoma Mountain Road in Sonoma County, near Glen Ellen. 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 road had been struck by a major landslide in the past, damaging about 600 feet. The failure was attributed to the poor native soil and excess moisture which left the ground saturated and unstable. According to online data, Sonoma County first selected a retaining-wall solution to repair the damaged roadway. Engineers built a 20-foot-high corrugated steel wall and supported it with steel H-piles driven into the slope. But the repair was made in very bad conditions. The project was abandoned in December 2008, following heavy rains, and the affected stretch of the road was finally closed in January 2009. The failure prompted county officials to rethink how the unstable slope could be repaired with less excavation and lower overall reconstruction costs.
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