A segment of the right southbound lane of Highway 101 on the Willits Grade is
cracking and starting to slip away from the rest of the road. Caltrans photo

Once again the unstable clay soil of the Willits Grade north of Ukiah is bedeviling Highway 101 and Caltrans engineers, but this time they hope they can beat it.

“Caltrans has been fighting it for many years,” with construction crews regularly fixing slipouts and other problems on the Willits Grade caused by the shifting ground under Highway 101, spokesman Phil Frisbie Jr. said.

The latest trouble is a slipout in the right southbound that has left the road cracked and starting to pull away from the rest of the highway. It has forced Caltrans to restrict traffic to one-lane in each direction along a 2.1-mile stretch of 101 south of Ridgewood Ranch Road.

He said construction crews started preparations on Monday for emergency repairs and excavation of the site could begin Wednesday, weather permitting.

Crews plan to dig down to stable dirt and to use layers of expanded polystyrene blocks and of dirt to fill the gap. Frisbie said normally crews would repair the slipout by trucking in tons of dirt, compacting it and repaving the road. But that sometimes just puts weight and pressure on the subsoil and leads to more slipouts, he said.

This time, he said, the light styrofoam blocks will sharply reduce the pressure on the subsoil and should keep the segment of Highway 101 stable.

How long it will take to fix the highway will depend on what Caltrans geologists find as crews dig down and on the weather, but he said current expectations are that the highway will be back to four lanes in six weeks.