By Summer Derrey and Meagan Lott
UPDATE Wednesday, Jan. 17
Two of the most common questions we’ve received in regard to the Rattlesnake Ridge slide are:
- What is a “slow-moving” slide?
- Why can’t you just blast the hillside and be done with it?
When we say “slow-moving” slide, we mean it could take months before it stops moving. Geologists currently monitoring the slide don’t expect it to release in one large mass. How do we know? The data we’ve collected shows it moving at a rate of 1.6 feet a week.
Which brings us to blasting. From the outside, it makes some sense. Drop some charges, trigger the slide and then clean it up. But, it’s not quite that simple.
If we start removing material or blasting it from the hillside, it will actually make the area more unstable, creating fissures in other areas and would likely release larger amounts of debris in an uncontrolled manner. For some perspective, we’ve spent the past several years blasting rock from the hillsides along I-90 as part of the project to stabilize rock slopes and add more lanes. When we blast, it’s in very small sections and then we excavate any loose material after the blast. Over the past five years we’ve removed a little more than one million cubic yards of material – or about 200,000 cubic yards every construction season (April through October). The Rattlesnake Ridge slide is made up of about four million cubic yards of material.
Also, blasting an unstable hillside simply isn’t safe. In order to do a controlled blast, crews need to drill into the hillside about 20 to 40 feet to put live charges into the hole. With the hillside moving, being able to drill accurately while also not causing more instability would be incredibly challenging. Even if the holes were drilled accurately, there’s the possibility that the charges won’t go off, meaning the crews would then have to sort through millions of cubic yards of debris looking for live explosives that could go off. It’s just too dangerous of a situation to put workers in.
So for now, we’ll keep doing what we’re doing. Workers continue to monitor the hillside, gather data and make preparations for when debris begins to come down.
UPDATE Friday, Jan. 12
We’ve joined with the Department of Natural Resources to select Wyllie & Norrish, Rock Engineers Inc., of Seattle as our third-party geotechnical firm. They have a combined 80 years of experience in specializing in rock slopes, landslides, tunnels, blasting, foundations and rock falls. The firm has already started analyzing data and will provide a summary with their conclusions later this month.
UPDATE Wednesday, Jan. 10
Last week our geologists began using 3-D Terrestrial LiDAR on the western slope of Rattlesnake Ridge to increase our monitoring of the landslide. Results from that monitoring are consistent with what we have been seeing with the movement of the landslide, and the new information helps us better understand the slide and its expected behavior.
With all of the information available, including the new 3-D LiDAR, we not only expect to see small rocks coming from the western slope but also large amounts of debris to sluff off. This amount may or may not be of sufficient quantity to reach Thorp Road. A visual change in the western slope doesn’t mean a change in the behavior of the landslide. It conforms with the current expectation for this specific slope.
We are still confident that the material coming down will not impact I-82 and the highway is still safe for drivers to use.
Partner agencies also providing updates:
- Department of Natural Resources - Rattlesnake Ridge site
- Yakima Valley Office of Emergency Management - Facebook / website
A slow-moving landslide east of Yakima has put many on high alert, including drivers traveling along I-82 adjacent to the landslide. There are several agencies working together to investigate, research and plan for this situation, and each has specific roles in preparing for the slide.
Our job is to protect the highway and make our best effort to help motorists avoid any obstacles on it. As the landslide moves, rocks could potentially fall onto the roadway. So far we have not seen any debris reach I-82. At the first sign of more movement or increased frequency of falling rock, we will close the highway. However, when dealing with Mother Nature, it’s hard to predict when this may occur. This is why we are working with local agencies as well as our crews to keep an eye on it.
|Contractor crews install freight containers along Thorp Road as a precautionary|
measure to keep rocks from hitting I-82 east of Yakima.
Should you take alternate routes right now?
We would close the highway if we felt it was unsafe. At this time those monitoring the situation have deemed the highway safe for travel and many of us are continuing to use it for our commutes. That said, everyone should make their own decision.
What would be the detour route?
If I-82 closes, several detours will be established. The local highway detour will be along US 97 from Granger to Union Gap and I-82 would be closed from milepost 58 to 37 until officials determine it is again safe for travel. Also, depending on the amount of debris that comes down, it’s possible that just the westbound section of I-82 would be temporarily routed along US 97. We’re preparing for all possibilities at this point.
|In order to weigh down the freight container, concrete barrier is placed inside of each container.|
What is WSDOT doing?
We are taking proactive steps to minimize impact to the highway and to drivers, including:
- Placing portable signs along I-82 to caution drivers of the potential for rockfall. So far, no rocks have fallen onto I-82, but we are monitoring the area closely.
- This week, our crews are installing a number of large conex/freight containers between Thorp Road and I-82 to provide rock-fall protection. Although each box weighs six tons, it won’t stop a landslide, but will protect against rocks.
- At the first sign of excessive movement or increased frequency of rockfall, I-82 will shut down as a precaution and traffic will be diverted to the detour routes.
You can view updates on the Yakima Valley Office of Emergency Management webpage and Facebook account. You can also call their office at 509-574-1900 and choose option 1.
While there are certainly a lot of unknowns with this landslide issue, multiple agencies with the appropriate expertise are working to monitor and prepare for all situations with public safety as our number one priority.