Just before the I90 pavement project started on Aug. 30 in North Bend between exits 31 & 32 started, Living Snoqualmie was asked by the Washington State Department of Transportation (WSDOT) if we had any questions about the repairs. We did and submitted our questions.
The next day, WSDOT completed the pavement project and answered our questions two days later. However, in the interest of not wasting an interview and perhaps answering questions the community has, too, we’re publishing the answers, albeit a bit late.
I spoke to Marcus Humberg, the WSDOT Assistant Communications Manager Northwest for Region Snohomish and King County Construction, about the long-awaited construction projects via email.
Why did it happen in the first place? You say it’s because of winter storms and flooding. Is that frost heave? Can you explain that?
We asked our bridge preservation team, and they listed several possible factors that led to this damage, but there’s no good way to tell which specific thing led to the failure. The harsh winter was a primary contributor, which is why it is covered under the Governor’s Emergency Proclamation issued on Jan. 8, 2022.
Once the pavement damage and potholing started, frost heave would definitely be a contributing factor to the damage we see today. Frost heave happens when you have repeated freeze/thaw cycles. Since water expands when it freezes, it creates larger and larger gaps that draw in more water through seepage and capillary action, causing even more expansion when it refreezes. Since asphalt pavement is not very flexible when cold, it is susceptible to cracking and spalling from ice and physical damage from passing vehicles during freeze/thaw cycles once it becomes compromised.
Is this kind of failure typical, or is there anything special about this one?
The type of bridge deck at this location is different than current construction techniques that use pre-cast girders. The deck itself is integral to the structure of the bridge. To protect the bridge deck, there is a layer of waterproofing material that goes between the concrete deck and the asphalt to prevent water intrusion that can damage the concrete.
The waterproof membrane itself is not physically bonded to the concrete deck; it is sandwiched between the asphalt and concrete. This is part of why the pavement failed the way it did once it was compromised. Also, there are extreme forces exerted from passing trucks decelerating and maneuvering around the corner at this location. So, in that way, this failure is somewhat unique.
Why wasn’t it fixed immediately? Why wait until so late in the summer?
Maintenance crews determined that temporary repairs using cold patch would almost immediately fail due to the forces exerted by heavy trucks braking on that turn, so temporary fixes were not possible.
This year’s historically wet winter and spring continued with rainfall persisting well into summer. The repairs needed to this section of the road require dry, predictable weather to be successful. Because our maintenance crews were not able to immediately address the issue, the repair was bundled into an emergency paving bundle funded by the Governor’s January Emergency Proclamation, and the project was sent out for bids from qualified contractors. We awarded the contract in late June, and it was finalized Jul. 14.
What is (was) involved in the fix? How long will it (did it) take, and what traffic delays were involved?
Our bridges team looked carefully at the repairs needed, and we took a minimalist approach to protect the integrity of the existing waterproofing barrier in between the asphalt and the concrete bridge deck. To do this, they ground out the sections that had damage, including some careful manual work to protect the waterproofing barrier, and then reapplied hot mix asphalt to create a permanent repair.
The repairs took about 8 hours for six separate sections of the bridge. I-90 was reduced to one lane, and traffic delays were minimal by design, as the work was done overnight.
More Major Freeway Closures
Now that we’re into the start of fall, two other significant closures on westbound Interstate 90 east of Issaquah are scheduled to start during the second half of September.
Water dribbling underneath Interstate 90 from an old coal mine has led to cracked pavement, with the water seeping to the surface of the interstate about a mile west of the High Point interchange.
“This coal mine was sealed off before we built this section of I-90, but over the years, water collected in it,” Wendt said. “Now that water is leaking out and seeping underneath the highway. That, combined with freezing in the winter and extreme heat in the summer, eventually cracked the concrete.”
To repair this, crews need to close the freeway for four full days and five nights the first week to remove the concrete, create a drainage system under the roadway, and repave it with asphalt.
The second week will require three full days and four nights. Crews are working during the week because this section of I-90 sees high-traffic use on weekends. About 29,000 vehicles a day use this portion of westbound I-90.
The closures east of Issaquah on westbound I-90 will take place:
- 9 p.m. Sunday, Sept. 11 to 5 a.m. to Thursday, Sept. 15, reduced to one right lane.
- 9 p.m. Sunday, Sept. 18, 5 a.m. to Friday, Sept. 23, reduced to one left lane.