I never imagined that tunnels would dominate the Seattle-area construction world so forcefully. But the array of tunneling options offer plenty of interesting fodder for the pages of ENR, watching crews plan tunnels for under downtown, below interstates and through waterways. These days, floating bridges serve as the only other construction method that so readily typifies the construction arena of Seattle.
In the upcoming edition of ENR, check out two articles chronicling two soil-eradicating techniques now in use in Seattle. While the planned bored tunnel under downtown Seattle to replace the Alaskan Way Viaduct will dominate the news for years to come, smaller projects give tunneling experts and contractors a glimpse of what is possible with the technology available and a chance to watch for lessons learned.
A simple sewer line replacement in the Ballard neighborhood of Seattle proved plenty more than simple when the contractor was unable to locate a slurry wall subcontractor to dig a vertical shaft deep enough (and for the right price). So the Pacific Northwest-based James W. Fowler Company turned to a German company for a Vertical Shaft Machine for the 145-foot deep shaft needed to launch a tunnel-boring machine for the sewer line replacement.
The German machine offers benefits never before seen in the PNW and gives contractors another option when it comes time to churn out the tricky soil of the area. I don’t want to give away all the secrets of the project (hey, I need you to read the ENR story when it comes out, right?), but needless to say, there are some interesting lessons learned in how a contractor can look outside the normal rubric to accomplish a task. Plus, it makes the project owner, in this case King County, pleased to see a bid-winner willing to make sure the job gets done as perfectly as possible.
Also in the ENR pages this week look for the news that JCM Joint Venture, led by Jay Dee Contractors, is tunneling just 13.5 feet under Interstate 5. Yeah, that’s super close. And pretty scary, too.
As part of a light rail extension from downtown Seattle to the University of Washington, crews had to navigate a 21-foot-diameter tunnel-boring machine through small openings in underground retaining walls (the landslide-prone area needs walls to hold up the earth) and then crawl just mere feet below Interstate 5. Using a combination of old-school methods of “listening to the ground” and the new technologies embedded on the TBMs of today, crews will inch under the interstate, hopefully with no ill effects to the road above. Check out my story in a few days to learn more about how they plan to pull this off.
As with both projects, some of the most interesting construction news in Seattle comes below the earth’s surface. Expect to learn even more in the months ahead. I know I’m looking forward to it.