A massive landslide on Topanga Canyon Boulevard in California led to an emergency cleanup and repair operation by Caltrans and Flo Engineering. After months of work, including straw wattle installation and debris removal, the project nears completion with hydroseeding being the final step.
Photo courtesy of the California Departments of Transportation
A Cat excavator removes landslide debris on Topanga Canyon Boulevard.
A massive landslide occurred at post mile 1.8 on State Route 27 (Topanga Canyon Boulevard) near Malibu, Calif., on March 9, 2024, closing the two-lane highway with a significant debris field.
California Department of Transportation (Caltrans) personnel were immediately on-site and, shortly afterward, the department hired Flo Engineering Inc. of Monterey Park, Calif., to handle the emergency cleanup and repair work.
Photo courtesy of the California Departments of Transportation
The roadway was cleared and reopened on June 2, months ahead of schedule. Follow-up work that involved installing straw wattles was completed on Sept. 26.
The remaining work consists of hydroseeding the hillside with native seeds in coordination with California State Parks. The vegetation will help keep the soil in place.
"Caltrans has completed the installation of straw wattles across the face of a bare hillside where a massive landslide occurred," said Jim Medina, a Caltrans public information officer. "It is a safety measure to prevent soil runoff during the rainy season. A fabric catch fence also was mounted atop k-rails to prevent rocks from falling on the roadway."
September was a busy month for Flo Engineering crews.
"Beginning Sept. 3, anchors were installed at the top of a steep slope where soil, vegetation and boulders came crashing down during a heavy rainstorm and covered a section of SR-27 in March," Medina said. "Crews tethered themselves to the anchors to attach and space straw wattles in advance of the winter storm season."
The landslide wasn't the first in the area, Medina said, noting that another one occurred nearby in the 1940s.
"The landslide that occurred March 9 is twice as large — the visible face is about 300 ft. above the roadway but extends about 200 ft. beyond that point into the brush," Medina said at the time. "Due to present geological conditions and instability of the slope, material must be removed from the top down. Removing the ‘toe' of the slope will bring down the unstable earth and large boulders above as water is still percolating under the surface.
"A boulder that is about 10 feet high that is visible from the south side of the landslide is a safety concern," he added. "A crack has formed behind it that is about 5-10 ft. wide, with the weight of the hillside pushing down on the boulder. A rough estimate of the landslide — just the visible face — is about 80,000 cu. yds. and 9.2 million lbs. This is enough material to fill 5,500 dump trucks."
Several hurdles had to be cleared before the debris could be removed, which had Caltrans and Flo Engineering personnel working as a team. These steps included Flo Engineering teams establishing a trail on the slope, which required thick brush to be removed; the placing of flags and the use of drones to provide detail footage of the surface; and having a loader cut through a section of the debris field to create a berm to protect a creek.
Photo courtesy of the California Departments of Transportation
A day later, drones surveyed the slide area, and a loader cut through a toe section of the slide on the roadway to collect the dirt, mud and rocks that was used to build a berm to protect a creek from falling slide material. California State Parks requested the berm.
At the time, Medina said: "Clearing some of the roadway will make room for loaders, bulldozers and excavators to begin clearing the slide at an undetermined time. The slide is still active and potentially dangerous, with soil clearly muddy and saturated. Our team from Geotechnical Services will begin mapping the slide. This will help us refine our recommendations and our initial calculations."
Heavy rains hampered those efforts.
The removal of the debris field began on April 29 and was completed on June 2.
"Flo Engineering built a zigzag path parallel to the slide to get heavy equipment, including a spider excavator, to the top of the hill to push down loose soil, rocks and boulders to SR 27," said Medina, "where super 10 trucks hauled away the debris at night to various locations to avoid disrupting daytime traffic on Pacific Coast Highway. Caltrans determined that attacking the slide from the top was the safest method to clear the area."
Safety was always top of mind.
"Tumbling car-sized boulders, slipping soil, seeping water and steep hillside were the prime safety issues," Medina said. "Workers had to wait for the saturated hill to dry out and become stable. The super 10 trucks were hauling away 60 loads a night. By the end, about 15,000 cu. yds. of debris were removed. It was unsafe to put workers in the path of the active slide until the hillside dried out. Soil, rocks and boulders continued to fall after the initial massive landslide on March 9."
On April 29, the debris field was deemed safe enough for excavators, dozers and other equipment to deal with the debris directly.
The soil, rocks and boulders were repurposed, with loads taken to a Ventura County farm, Los Angeles County roadways and an art institution in downtown Los Angeles.
"No debris went to a landfill," Medina said.
He said lessons were learned and best practices were honed via the debris removal operations.
"Mother Nature can be a monster," Medina said "Two winters of atmospheric river storms saturated hillsides in Southern California. Climate change is contributing to numerous landslides, wildfires, flooding and beach erosion. … Drones were invaluable for mapping the upper sections of the landslide in the weeks before workers could get to the top of the hill."
Photo courtesy of the California Departments of Transportation
In addition to the super 10 trucks, operators used spider excavators, front loaders, bulldozers and drones.
With the debris removed, and slope stabilized, it was time to install the anchors; that was completed between Sept. 3-9. The fabric catch fence to prevent rocks from falling on the roadway was installed afterward.
The hydroseeding operation has not been scheduled. Caltrans is consulting with the California Parks Department on the type of vegetation that should be sprayed across the hillside.
Flo Engineering's management team includes CEO Kristin Flores, and the Caltrans management team includes John Yang, Dan Leon, Steven Zaw and Matt Gaffney.
"The team dynamic was professional and efficient," Medina said. "The efforts of the crews were outstanding." CEG
Irwin Rapoport
A journalist who started his career at a weekly community newspaper, Irwin Rapoport has written about construction and architecture for more than 15 years, as well as a variety of other subjects, such as recycling, environmental issues, business supply chains, property development, pulp and paper, agriculture, solar power and energy, and education. Getting the story right and illustrating the hard work and professionalism that goes into completing road, bridge, and building projects is important to him. A key element of his construction articles is to provide readers with an opportunity to see how general contractors and departments of transportation complete their projects and address challenges so that lessons learned can be shared with a wider audience.
Rapoport has a BA in History and a Minor in Political Science from Concordia University. His hobbies include hiking, birding, cycling, reading, going to concerts and plays, hanging out with friends and family, and architecture. He is keen to one day write an MA thesis on military and economic planning by the Great Powers prior to the start of the First World War.
Read more from Irwin Rapoport here.
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