Devil’s slide and Shamrock Ranch slip-out are both deteriorating

Why wait till Wednesday?

Posted by on Thu, April 6, 2006

Wednesday afternoon, Coastsider visited the Devil’s Slide just 48 hours after our first visit on Monday.  We were surprised by the amount of deterioration both at the Slide itself and at the slip-out at Shamrock Ranch.

It was clear that in just two days the situation had become significantly worse.

The principal cracks in the pavement at the Slide were wider, the differences in the elevation between each side of the crack had increased from a couple of inches to six inches, the number of smaller cracks in the pavement had increased, and the whole section of highway at the Slide had become a noticeable dip in the road.

Meanwhile, the slip-out at Shamrock Ranch had gone from being a dip to a hole.

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Barry Parr
Cheri Parr
Monday: The concrete barriers were already displaced and lower than the pavement by about a foot.
Wednesday: The concrete barriers had sunk at least another foot so that their tops were even with the pavement and the gap between them and the pavement has increased greatly.

Click on the link to see more comparison photos.


Barry Parr
Monday: The large longitudinal cracks were about for inches wide and the cliff side of the crack was a couple of inches higher than the ocean side.
Cheri Parr
Wednesday: The cracks were about 8 inches wide and the elevation difference was about 6 inches.  You can also see in this picture how the road dips noticeably on the southern side of the white paint line that marks the slippage.


Darin Boville
Sunday: This picture shows the Shamrock Ranch slip-out on Sunday afternoon, when it was a dip in the road. The slip-out is on the left side of the road in this photo.
Cheri Parr
Wednesday: The dip had become a hole and the shoulder had fallen even further from the road.

I hope and Pray CalTrans will fix the two slumps starting to get worse on Hwy 92 - One is at the perpetually wet curve just inside the HMB city limits - the other is up by where the big puddle of water is - not far from where the eucs fell over.  We do not need Hwy 92 looking like the photos in this set.


Regarding the slip-out at Shamrock Ranch: Is there any chance that the slide there was precipitated by Caltrans’ building of the contruction access road which leads away from highway at that point?

The access road is cut into the hillside below the level of the highway, which, when combined with the extra soil weight from the rain, may have de-stabilized the hillside.

See photo #‘s 108, 112, 114, and 116 in the album.

Barry, in addition to the broad “Police & Fire” category, is is possible to add a category for “Devil’s Slide” and categorize these stories that way, too?  From a reader’s perspective, would be nice to have one link to go to in order to grok all the latest news on what’s going on.  Just a thought.

Not sure this is the best place to post, but here goes:

At the harbor stoplight (Capistrano) and at Coronado, those turning L onto the highway effectively have priority over those who are already on the highway.

Can we get the County Sheriff to provide traffic control at those two intersections?  If the traffic flow is more equitable, then the travel times from Montara/Moss Beach won’t be quite so insane. 

On Monday, I was the 2nd car in line at Capistrano.  After five full cycles of the stoplight, I HADN’T MOVED.  I was STILL the 2nd car in line at the light.  I turned around and went home!

In my experience, the flow of traffic was much better once I got past Coronado.

The barricades and traffic controls really helped a lot yesterday!  Still, it took me 2.5 hrs to get to my office in S San Jose.

Very interesting images.  Good way to fact check the CalTrans spokespersons.  I’m no professional, but here goes. 

Shamrock slump doesn’t look that major.

Slide images are more troubling.  The images of the boulders and slumping K rail are dramatic.  But, that’s not the real problem. Looking first at image 3401.  Slumping runs across the whole roadway.  This is just not a matter of the edge of the South Bound lane slipoff.  The problem is across the whole roadbed.

Looking at the following photo’s there are
lots of CalTrans reference marks on the pavement. There must be a reason for this.  Photos measuring the cracks are a real good idea.  That is what CalTrans is doing.  Image 3413 show four cracks running paralell to the direction of vehicular traffic. These appear to be located along the cuts for the sensor wires.  I’d speculate those cuts became the stress risers where fractures of the pavement occured.  The motion is causing a stretch across the whole roadway just south of the CalTrans painted white line.  I’d guestimate from the photos it’s something like two feet West and two feet down. One way to view this is there is a subsurface tear below the faint white spray paint line on the pavement in image 3413 the direction of travel is toward the person in the picture. The roadway south of the white line in image 3413 and up the slight incline(toward the camera)appears to be swinging uniformly toward the person with no major fractures.  It would have been encouraging to see some fractures to the south of the pavement fracture area. That would have indicated the slump area was small perhaps caused by the dynamic load of vehicles bottoming out where the oil spot is on the pavement.  But, I don’t see evidence of that.  There may be movement on a fairly large scale south of the fracture area. That whole southern area may be swinging west and down uniformly.

The concrete/gunnite hillside cracks to the south don’t appear that large. There is movement but not on the scale of Image 3413.

The Monday photos showed CalTrans filled in some of the cracks with asphalt patch to keep the rain out.  That’s prudent for an edge slipout.  But, pointless for a deep slipage. The fact they didn’t bother to fill Wednesday, could be an indication of how deep they think the problem is.

In summary, Image 3413 tells the story to me.  I think CalTrans has to do some Geotechnical exploration to find out the extent of the movement. It’s pointless to talk quick fixes or steel spans until, someone determines a stable place to anchor it. So, for the time being, I’m buying CalTrans’public comments.

Vince Williams

p.s. Thanks for the great coverage. I hope you have a spotter to warn you where to run from the falling rocks.  Hardhats and a more substantial tape measure would improve your images.