Why is Highway 1 cracking at Mud Creek?
When the slippery slope above Big Sur’s Mud Creek slid catastrophically on May 20, 2017 — ultimately burying a quarter mile of Highway 1 with up to 40 feet of mud, rocks and more — U.S. Geological Services scientists already had been tracking the earth’s movement there for decades, according to a recently published study.
What’s more, some of the USGS technologies that detected the earth movement as far back as 1967 also helped keep workers safe during the $54 million repairs to get the roadway re-opened — and the tech is continuing to track potential landslide problems.
Because Mud Creek, Paul’s Slide and other landslide-prone areas of Highway 1 between Cambria and Carmel aren’t out of the woods yet, said John Madonna of John Madonna Construction, which did most of the repairs.
Even if it doesn’t rain any more this season.
Landslides frequently happen when it’s not raining, he said. A major slide “could happen now or in May,” as was the case in 2017. Madonna explained that the danger time is when wet soil starts to dry out, losing the surface tension that keeps things in place.
“It’s like when you take some dry dirt in your hand. Pick it up, squeeze it and let it go. If the soil is totally dry, it will go through your fingers and fall out of your hand. If there’s some moisture in there, it will stay in your hand,” he said.
As his dad, Alex Madonna, told him, “Without any moisture, there’s nothing to hold it together. Even sand will make a ball if there’s some moisture in it.”
John Madonna Construction, Caltrans and others are continuing to collaborate and work on Highway 1, especially in the Paul’s Slide section.
“That was the big slide before Mud Creek,” Madonna said, but even after the repairs were done, the “angle at Paul’s Slide was unsustainable.”
Now, he believes “we’ve found the sweet spot” to increase stability of the steep banks above the roadway.
“I’m really excited about the success that I believe Paul’s Slide is going to be,” he said, “and we should be done with that work by the end of summer.”
There’s still work being done at Mud Creek, too. Monster boulders are being hauled up Highway 1 to bolster the base of the retaining wall there, Madonna said. He said they’re reevaluating to see what else can be done in the next few months to increase stability and safety.
“A tremendous amount of energy came down in Mud Creek,” he said. “We think there’s more up there. There are a few pockets that we’re kind of wondering what they’re going to do.”
With the work completed last summer, he said, “we did the foundation,” but the rest is up to Mother Nature. As for other options, Madonna said, “if we took the same approach at Mud Creek that we did at Paul’s, that road could be closed for a couple of years.”
“Everybody knows there were businesses struggling” during the closure, he explained, visitors who weren’t visiting and locals who were cut off or disconnected because the highway was closed. “The two projects are totally different animals,” he added.
For instance, he said, “Paul’s Slide has a fracture that goes into the mountain for 200 feet.”
Crews built a “tremendous wall” there, Madonna said, but Mother Nature has already begun to move it.
Safety and other tech
Ultimately at Mud Creek, Caltrans and John Madonna Construction used ground radar, aerial LiDAR, GPS measurements and other tools to design a $54 million project that created a 2,000-foot long, 40-foot tall rock revetment at the shoreline. They used engineered embankment berms, catchments, culverts, netting and more to create a new roadway on top of the slide material.
“There was amazing technology,” Madonna said. “A Canadian company does satellite images all over the world. It flew over that area once every 28 days”
That produced images that helped engineers plan the project and Madonna crews produce it safely and ahead of schedule.
He said there were robotic stations with prisms to measure movement, and he estimated that Caltrans “probably spent a half million dollars to rent” just the radar systems.
And what’s LiDAR? It works in much the same way as radar systems do, except LiDAR uses laser instead of radio waves. Madonna said LiDAR “doesn’t recognize vegetation,” so it produces kind of “a grayish topographic of the contours without vegetation.”
He described radar as “tracking movement.”
“We were grabbing every tool in the tool box,” Madonna said. “We used high tech and low tech and everything we had. There were tools I never knew existed.
“We used all kinds of technologies to keep us safe up there,” he said, even proven low-tech methods, such as “a ground spotter who sat there all day, looking for rock movement.”
The spotter used a warning horn and broadcasts to the 30 or 40 radios on site to alert workers about potential problems and dangers.
Madonna’s company was notified last week that the Mud Creek project will be awarded by American Public Works Association with a national honor, which will be presented in Seattle in September. The project also won the local chapter’s award for projects of $50 million.
“I feel really weird about taking a lot of credit,” Madonna said. “It was a team effort, not just John Madonna Construction that made this happen. We helped. There were a lot of people working in a lot of different directions: subcontractors, engineers, biologists, oceanographers, so many people working long and hard to get the project done. ... A lot of people really set their lives aside for a long time to get this done.”
The USGS study
USGS researchers used air photos, drone photos and laser scans to precisely map the slope that ultimately dumped more than 22 million tons of earth on the road and adjacent areas below, temporarily creating 13 acres of new California real estate, according to Rex Sanders, a USGS spokesman.
During the year-plus repairs, “continued monitoring helped Caltrans keep workers safe as they rebuilt the road over the top of the slide,” Sanders said.
Caltrans spokeswoman Susana Cruz said that “as part of the geologic study of the landslide, USGS used air, ground and marine-based surveying and mapping techniques to collect geospatial data about the pre- and post-slide conditions at Mud Creek.”
She said Caltrans District 5’s “Geotechnical Design Branch has a long history of working and collaborating with the USGS, and those personal relationships help forge a quick path toward information sharing.”
When Caltrans was in the early alternative evaluation and design phases of the project, “USGS geologists graciously reached out and shared their data,” Cruz said.
“Their data and presentation tools were incredibly useful information that helped guide our decisions about how to best approach reopening Highway 1 and eventually choosing the most time- efficient and risk-balanced alternative.” And the technology and science will continue to contribute, Sanders said, as “relatively cheap air photos and new computer software developed for this research could help spot future coastal landslides.”
Cruz said that, after Caltrans collaborated with the USGS and learned about some of the technologies they implemented, the state road agency “has utilized subcontractors and developed internal programs to provide additional second and third slide mapping to track the movement and changes to the Mud Creek Landslide.
“Continued monitoring, observations, and mapping are planned as Caltrans engineers, geologists and maintenance personnel focus our efforts on maintaining and proactively managing Highway 1 where it traverses the still-active Mud Creek Landslide.”