By John Schneidawind, vice president of public affairs, ARTBA
When a 150-foot chunk of California Highway 1 near Big Sur fell into the Pacific Ocean on Jan. 28, it was anybody’s guess when the scenic stretch would re-open to traffic. But the road opened April 26, months ahead of the originally projected summer completion.
All it took over those 86 days was some shrewd decision-making and hard work, plus tons of fill and a few extra culverts.
Wildfires high above the coastline in fall 2020 “scoured out the watershed above,” said California Department of Transportation (Caltrans) engineer Victor Devens. When torrential rains came in late January, it was only a matter of time before the watershed came washing down onto the highway, clogging the culverts where water would normally flow. The water and debris sloshed over the highway, weakened the fill supporting it, and the highway buckled.
The conditions that created the gaping hole in Highway 1 were unique. As Caltrans first surveyed the damage, it was unclear whether restoring the road would be like “trying to keep the (existing) road onto jello pudding,” Devens said.
Highway 1 stretches 656 miles between Leggett in Mendocino County in the north, and Interstate 5 near Dana Point in Orange County in the south. It was built in segments, starting in the 1930s. At Rat Creek, in Monterey County, Caltrans faced a key decision in repairing the damaged highway: build a bridge across the chasm or put back the dirt that had supported the roadway in the first place.
The agency chose the latter approach. This “enhanced fill option” involved replacing the main drainage system at Rat Creek with a 10-foot diameter main culvert, a secondary culvert, and smaller overflow culverts closer to the highway grade. This increased the capacity of the drainage system, added redundancies designed to withstand future debris flows, and enhanced the resiliency and sustainability of the highway against rising seas and coastal erosion.
“The fill solution is one-quarter to one-third the cost of trying to do a bridge,” Devens explained. “This wasn’t a foundation failure; this was a culvert being scoured out.”
Before Caltrans could introduce new fill to the repair site, however, it had to remove the debris of trees and other vegetation that tumbled down onto the highway, making the fill area unstable. By late March, an estimated 70,000 cubic yards of trees, rocks, and sediment were removed from the canyon below Highway 1 and taken off site.
Then, 25,000 cubic yards of new fill were trucked in to build support for the new roadway. Caltrans spokesman Kevin Drabinski compared the effort to building a home, an earthen foundation needed to be created at the bottom of the canyon to accept the fill. Working seven days per week during daylight hours, crews constructed steep paths on the north and south side of the canyon to haul the fill material.
Engineer Devens suggested the $15 million effort won’t need to be repeated. “Geologically, the area is pretty stable,” Devens said. “I’m very confident we won’t have this happen again at this location.”
As of the late April reopening, the highway still required a permanent guardrail and some other erosion control.
An earlier version of this story appears in the March/April issue of ARTBA’s Transportation Builder magazine. This version includes reporting from The Mercury News. Photo: Caltrans image of project site.