Caltrans Continues Work on Retaining Walls at Last Chance Grade; Emergency Project Expected to be Finished Later This Year | Wild Rivers Outpost

Jessica Cejnar Andrews / Wednesday, March 16 @ 11:51 am / Infrastructure, Roads

Caltrans Continues Work on Retaining Walls at Last Chance Grade; Emergency Project Expected to be Finished Later This Year

Caltrans crews work on a retaining wall below US 101 at Last Chance Grade in November. | Photo courtesy of Caltrans District 1

Caltrans crews have finished shoring up Last Chance Grade following the slip out that sent 45,000 cubic yards of debris onto US 101 last year.

But work continues on two retaining walls Caltrans representatives say are necessary to maintain the road’s resilience. Once those walls are in place, Caltrans envisions being able to remove the temporary traffic signal that has been there for the past eight years.

Though he couldn’t give an exact date, Clayton Malmberg, Caltrans District 1 construction supervisor, said construction on those walls should be finished late this year.

“There’s been multiple sections within that roadway that has had huge slip outs, resulting in the need for walls of different types to help keep the road open,” he said. “Work on that began before that big slip out and is continuing now.”

According to Malmberg, Caltrans crews are using large horizontal concrete beams and tiebacks to anchor the two walls into the soil.

The first wall, Wall 7, is on the uphill side of the roadway, while the other wall, Wall 5B, is underneath US 101.

Work on the two retaining walls is part of an ongoing emergency project that began before the massive landslide that shuttered US 101 last year, Malmberg said.

In response to that slide, Caltrans installed a cable drapery system once the debris was removed, he said.

“We did complete that work in the fall as planned,” Malmberg said.

Jaime Matteoli, project manager for efforts to route US 101 around Last Chance Grade, said the two walls increase the highway’s resiliency.

“The philosophy is not that the walls will stop or arrest movement of the slide, but they maintain the geometry of the road,” Matteoli said. “Even if there is movement, it’s sort of holding the road together as movement occurs so it increases the resiliency of the road.”

Meanwhile, Caltrans is still determining the feasibility of two options for a “permanent fix” to Last Chance Grade. One involves bypassing the landslide via a tunnel. The other option involves re-engineering the highway near the current alignment.

Caltrans is on track to deliver an environmental document on the two alternatives in 2025, Matteoli told the Outpost.

“We met with key construction members, people that do structures construction and roadway construction and people taking care of managing and rebuilding the road right now,” he said. “And the next key step, as we’re wrapping up our environmental studies here very soon, we will begin writing technical reports that feed into the draft environmental document. That document will be produced and circulated by the end of next year.”

According to Matteoli, Caltrans is continuing to have conversations with its working groups to mitigate project impacts. This includes determining where large old growth trees, wetlands and other sensitive habitat is to minimize the tunnel’s potential impact.

Matteoli said Caltrans is also working on the second alternative, which would keep US 101 largely on the same alignment. Known as Alternative X, this alternative involves an “end-to-end re-engineering of US 101, moving the road inland by about 130 feet while installing retaining walls and better drainage to divert water away from the hill.

“The other portal, we’re honing it so we can have a crystal clear project description,” Matteoli said, “so we can describe how construction’s going to build it and then describe what those impacts are. We expect that within the next few months. By May, we’ll have clear internal project descriptions that we can use for beginning our technical reports.”

Caltrans will hold an open house in the next few months. According to Matteoli, the project is funded through the environmental phase. There is no funding for the design or construction for the project yet, he said.

Documents:

• Alternative X and F fact sheet

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