Photo courtesy of Caltrans
An excavator prepares the landslide site for remediation efforts.
Efforts by R & R Demo and Grading Corp. and the California Department of Transportation (Caltrans) are ongoing to repair damage caused by a major landslide that occurred on Feb. 21, 2024, on State Route 150 in Ventura County and to prevent future incidents.
The landslide, which impacted approximately 1.8 acres just north of the city of Santa Paula at Bridge Road (mile post 31.4), happened about 3 mi. north of State Route 126.
Photo courtesy of Caltrans
Work is continuing but is no longer on a "nonstop" basis — which was the case before SR 150 reopened to traffic on July 31.
"Opening the highway had been an absolute top priority following the landslide," said Michael Comeaux, public relations officer of Caltrans District 7. "Crews worked seven days a week before July 31."
The slide occurred during powerful storms that saturated the region. The approximate dimensions from the head scarp to the toe is 750 ft., and it ranged in width from 100 to 200 ft., according to Caltrans. This part of SR 150, which connects Santa Paula and Ojai, is used by more than 3,200 vehicles daily.
The debris field brought down earth, rock and trees. The field was at least 25 ft. high, and a large amount was strewn along the slope. The landslide avoided overrunning most buildings except for a water plant serving farms and orchards in the rural area, Caltrans said.
After multiple soil tests, Caltrans began building a soldier pile retaining wall.
"Work is still ongoing, and occasionally there will be a one-lane closure to facilitate the remainder of the construction," according to Caltrans.
Caltrans designed the project and completed a set of plans.
"While the designs and reviews were ongoing, Caltrans sourced all the material that we needed to complete the project, including beams, wood lagging, fabrication shops, etc.," according to Caltrans. "The retaining wall needed to support this slide is 360 feet in length with a height of 40 to 50 feet. Multiple rows of ground anchors extending up to 150 ft. in length are being constructed through the face of the wall and extend through the slide plane for anchoring the wall."
The state DOT stressed that this was no run-of-the-mill operation.
"The hillside consists of multiple nested slides, which have moved in the past leaving exposed visible scarps," said Caltrans. "The slide movement in February deposited slide debris on State Route 150, debris which is currently acting as a temporary buttress to support the material uphill, both vertically and laterally. More slides could occur if material is removed from Route 150. Caltrans is closely monitoring the active slide and the adjacent areas for additional slope movement. Caltrans also hired a [contractor] to install a system that detects further movements in the slide during construction."
Due to the unstable slope, Caltrans warned that operations had to proceed slowly and assembled teams of experts in design, construction and emergency operations.
Photo courtesy of Caltrans
"Caltrans started this complex investigation process immediately after the slide occurred," it stated. "Caltrans secured the area and monitored the slide for further movement, and Caltrans continues monitoring it closely. Caltrans immediately developed a plan of action for reopening Route 150 as quickly as possible."
Also, Caltrans immediately started the geotechnical investigation of the slide area and quickly arranged an emergency contractor to provide additional equipment and workers.
This is not the only section of SR 150 experiencing similar issues. Near the Dennison Grade, material came down a slope and, near Thomas Aquinas College, there was a slip-out.
According to Caltrans, "It is safe for motorists to drive these sections and crews are closely monitoring Dennison Grade and removing any materials that can pose a hazard to motorists and cyclists. The slip-out about one-fourth of a mile south of Thomas Aquinas College has been repaired."
"Crews have been making progress drilling holes with two rigs for the 45 piles [ranging from 65 to 75 ft.] that make up the soldier pile wall," said Eric Menjivar, PIO, District 7, in a May 10 update. "So far, the contractor has drilled, set beams in place and poured concrete at 13 locations. They have already drilled two other locations with one still in progress."
"The contractor is done with drilling, setting beams and pouring concrete at the 45 locations and will begin hauling the debris out from the drilled holes," said Alisa Almazan of Caltrans in a May 24 construction update. "Next, the contractor will begin excavating between the piles to begin installing the wood lagging for the soldier pile walls."
Since that May update, many benchmarks have been met.
With the road closed, crews had ample space to work. R & R moved equipment about easily as the debris was removed and operations began on the slopes to install the retaining wall, Almazan said. This was crucial as many large pieces of equipment were brought in, such as Mait HR 165 and Bauer BG11H drill rigs used by McMahon Drilling, a subcontractor; and large LiuGong 936E excavators, mini-dozers, various loaders and other standard equipment.
The debris removal operations were handled by large excavators, including LiuGong 936Es and mini-dozers.
"The removal of debris commenced as soon as conditions allowed in February after the slide on both Santa Paula and Ojai," R & R team said. "Slope work was continuously performed and carried out throughout each phase of the construction. Debris was hauled from both the Santa Paula and Ojai sides immediately following the slide."
Installing the soldier pile retaining wall is a challenge.
"This is an unusual slide," Comeaux said. "Not only are there multiple slides in the area, but it also is very deep. For a typical wall with tiebacks, the tiebacks are usually about 50 to 75 feet long going into the hillside. For this wall, the tiebacks go back approximately 150 feet. These two factors are the main contributors to our difficulty in drilling, placing, grouting and testing of the tiebacks. Also, we encountered water in some locations in the hillside as we drilled.
"Caltrans determined that the highway could be reopened after two rows of anchors were in place," he added. "We still have three other rows of tiebacks to install. The wall is 360 feet long and at its tallest is about 35 feet high. There are a total of five rows of tiebacks. The first two rows each have 45 tiebacks. Those are the first two rows that were installed, after which the road was opened to traffic."
Everyone is on the same page regarding the work, both Caltrans and R&R said.
Photo courtesy of Caltrans
"Relations between the general contractor, Caltrans, local farmers and agriculture, in addition to residents and influential community members, was a priority during the entirety of the project, and still is to the present day," R & R said.
R & R added that the project was no ordinary job.
"One of our biggest priorities was to construct and keep an emergency lane open at all times," it said. "With the collaborative efforts of our staff, subcontractors, Caltrans and positive local community engagement, the road was able to be opened in just five days rather than the 10-day deadline. To do this, we ran trucks and had our crews here running seamlessly for 24 hours."
805 Trucking assisted R & R with hauling and Santa Paula Materials provided excavation and recycling services.
All equipment used on the job — John Deere, Caterpillar and LiuGong — is owned by R&R. No rentals were used, and machines were all serviced on-site by qualified mechanics. 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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