Experimental helicopter water drops at Regents Slide were scheduled but ended up being during recent rains, which appears to have done something. The upper, dirt portion of the slide is moving on its own every day. I think some tens of thousands of yards came off over the weekend.
Here’s a recent summary I sent to my institution a month ago.
Caltrans geotech has heavily-instrumented the upper portion of the slide due to its continuous movement. The movement has made it very hazardous to remove so equipment has been put on and pulled off the working bench repeatedly over the past few months. The attached photo shows the upper slide as of February 3rd, circumscribed in orange dashed lines. The original slide is on the back (south) side of a rocky, resistant ridge and well below this upper area. Debris from that rockslide can be seen 500 feet down on the highway on the right side of the photo.
The plan has been to start above the rockslide section and cut it out using a working bench. The cut material gets pushed over the edge, gradually working downhill back to the highway. The upper slide section was destabilized by that process and started “rotating”, slipping downhill and outward, pushing over the resistant rocky ridge below. The arrows in the photo are my attempt to depict that rotation. The weight of the upper area to the left is causing the material to slide downhill but it is encountering the resistant material below. That is causing it to actually move horizontally and outwards to the right and to push out into the air, calving off like a glacier reaching the ocean or a lake. You can see there are two new slide sections at the horizontal arrows where the dirt is flaking off and falling down to the highway.
Excavation is on hold while it rains. There is a presumption that as the soil gets heavier with water, the material will accelerate (not catastrophically fail) and reveal exactly where the slip plane is behind the slide. That will allow them to have a better defined plan moving forward. You can see their graded slope in the upper left of the photo. They need to keep that slope behind the slip plane as they work their way down to the right.
Changes over the last month involve more dirt being pushed off the bench onto the slide (head) and the lower right (toe) calving off down to the highway. Also see attached two photos I took during the rain last week. Beneath the remaining vegetation there are fissures criss-crossing the moving section. It acts like a glacier, slipping off the top of the lower part of the larger slope, calving off the mountainside about 400′ above the highway. Impossible to put equipment on it when it’s wet. They monitor it daily and pull off when it accelerates and jump back on when it slows down.
That’s the latest from ground zero,
Mark
Here are the photos Mark references:
March 12, 2025 by Mark Readdie
March 14, 2025 by Mark Readdie
And from yesterday, March 18, which shows the recent drop:
Something I forgot to mention probably because I recycled a month old update. In addition to the two excavators and two other dozers, there are an additional two D8 dozers that have been retrofitted to wireless operation because Caltrans is pushing Papich to keep pushing dirt over the slip-plane crack but having an operator in the machines is too dangerous. The scale and complexity of this slide has pushed Caltrans into new technological territory in order to keep making progress. Perhaps a photo of all the equipment working on the slide would provide some scale. I’ll have to see if I can get that this week.
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Maybe the top down approach isn't going to work. Just a thought. Afte 2 years of failure, it seems a new approach should be taken.
My intention here is to provide a factual update so folks can have as much information as possible to set their plans and expectations. I appreciate what we are all going through for the last year in all the various ways. Hopefully a bit more info from the site can be helpful to you. -Mark
My guess is that the natural slope is fairly close to 1:1 (1 1/4:1?). Mark, what is the natural angle of repose range for the relevant materials, both natural and unconsolidated/fill under the range of conditions expected (including seismic activity)? Are any arrangements for subsurface drainage being done or planned? What kind?
Thanks for this Mark. I’m glad to hear some equipment is moving dirt. I’ve been picturing shipping containers set up to protect excavators at highway level working from both sides. Some material could be removed and trucked away. I’d love to see some drone footage!
avalanche technique. Dynamite the slide. Haul the dirt away. Pave the road.
This road is cursed. Build a byway around it. Rebuild the coast ridge road.
These are temporary fixes.
Nature bats last…
I tend to agree with Tierra. What is the cost per vehicle count to maintain this road? How does it compare with other highways in this respect?
Have they ever considered using explosives?
call trans is a virtual back hole leading to no where. AI (artificial Intel) would likely offer much more in solutions. It would be programmed to combine all previous landslide/rebuilds into a scenario most closely representing this one.
Internationally, there is likely a history of rebuilds similar to Sur's..in that archive there a chance of finding a scenario closely resembling ..What's my guess for a perfect fix? Begin at the bottom..grade, in a curved shape, tier it so the slope itself will offer enduring supportive strength..it will require drainage, more rebar then our minds can imagine, and concrete out the ying-yang.. That's only one half, for the upper reaches far above the lower road, will need to be stabilized just as aggressively. Perhaps with a design as Esalen used to stabilize the slope rising steeply above the bathhouse.
What Im imagining is entirely an uneducated approach..just reaching a little ways into my dream state.
I think it's worth noting that this rotating, constantly moving upper slide is hanging 700 feet above the ocean, being held up by a series of rocky cliffs whose stability is unknown. Papich and their operators are on that upper bench, pushing dirt to the brink of the slip plane (and over it) under the spectre of Mud Creek's catastrophic failure. Caltrans's geotechnical engineer is doing the science trying to understand whether this is a creepy-crawly situation or a catastrophe waiting to happen, taking the operators lives and safety into his hands so that Caltrans can decide to keep working on the slide through the winter and the "landslide season". I've been living with these operators for the past year, seeing and hearing the concern and anxiety they are managing every day they're told to get in the tractor. To respond to the pressure to keep pushing dirt for everyone else's sake, this is the most instrumented slide Caltrans has ever had. They can monitor how much it moves every day and make calculated predictions to inform when it's "safe" or not to put heavy equipment on it.
At the same time, a team of landslide scientists now have funding to focus on better understanding this very situation, and to inform engineers throughout California on how to address the coastal highways, housing, etc. while increased rain intensity washes away the coastal mountains and bluffs and the ocean eats away at their foundations. I introduced UCSC professor Noah Finnegan to the Caltrans geotech and they will be working together with a direct link between the research results and engineering decisions for the future.
See link to article here:
https://news.ucsc.edu/2024/10/landslide-earthquake-prediction.html
Everyone is absolutely aware that right now nature has a home-run slugger up to bat and the engineering solutions for keeping these coastal highways open needs to level-up.