Bremerton Gets a Tunnel
It's not on the scale of Boston's Big Dig, but the Bremerton Tunnel Project nevertheless is poised to make a significant impact on traffic in this waterfront city across Puget Sound from Seattle.
Tri-State Construction Inc., of Bellevue, WA, is the general contractor on the $30.7-million project to build a two-lane, 950-foot-long tunnel to carry off-loading ferry traffic under a congested area of downtown Bremerton and connect it with State Route 304. Exeltech, of Lacey, WA, designed the project for the Washington State Department of Transportation.
The tunnel will separate downtown Bremerton pedestrian traffic from offloading Washington State Ferry vehicle traffic. The periodic surge of ferry traffic through downtown Bremerton is interfering with pedestrian and local traffic flow including access to and from the Bremerton Transportation Center and the Puget Sound Naval Shipyard. In addition, substantial improvements to the city's downtown core, including a new conference center and hotel complex, office buildings, a park and a memorial plaza, are generating a considerable increase in pedestrian and motorist activity downtown.
Currently, pedestrians wanting to cross downtown streets in the vicinity of the BTC are hindered from doing so for as long as 10 minutes at a time while vehicular ferry traffic offloads. As a result, pedestrians have been known to dart out into oncoming traffic, while others simply avoid coming downtown altogether. With downtown improvements drawing a significant increase in pedestrian and local vehicular traffic, this challenge is expected to multiply. This project will address safety concerns by removing approximately 65 percent of offloading vehicular ferry traffic from the Washington Avenue waterfront area, according to WSDOT estimates.
WSDOT is in partnership with the city of Bremerton, Kitsap Transit, the Federal Highway Administration, and the Federal Transit Administration on the project. Other organizations participated in its development as well, including the Puget Sound Naval Shipyard and local emergency services.
In addition, the design and construction of the city of Bremerton's combined sewer overflow project has been coordinated with the tunnel project. The CSO is needed for the city of Bremerton to comply with the state of Washington's municipal waste discharge regulations and to reduce combined sewer overflow events in the Pacific Avenue Basin to an average of no more than one per year. The CSO project includes two specific improvements: construction of a CSO trunk line from the intersection of Fourth Street and Park Avenue to an outfall located at the BTC, and construction of a storm water collection system to reduce the frequency of combined sewage flows in the basin. By coordinating the design of the tunnel and the CSO trunk line, significant savings could be realized in the CSO project.
Cut and Cover
Brenden Clarke, project engineer for WSDOT, described the tunnel design as a self-supporting concrete box structure, built by the cut-and-cover method. Each of the 17 concrete segments measures two lanes wide, 55 feet long and 16-1/2 feet high. The tunnel is a constant height except in two places where it's higher to accommodate jet fans for the pass-through ventilation system.
The project began in July 2007 with the demolition of four buildings at the north end of the tunnel, following by demolition of a large building at the ferry terminal end, said Ryan McBride, project manager for Tri-State Construction. Utility relocations then got under way and revealed several surprises, including underground tanks, asbestos, the remains of a burned-down building, and a buried garbage dump containing two Model-T Fords.
"They were pretty well gone, but the engine blocks were still there," McBride recalled.
Tri-State is self-performing excavation, concrete work, earthwork, and piping on the project. About 40,000 cubic yards of material is being excavated for the tunnel. The work was sequenced in two phases, with the northern half first. About 8,000 tons of soil in the first phase area was found to be contaminated and had to be removed from the site. The volume was greater than expected, WSDOT's Clarke said, even though extensive soil testing had been done prior to the start of construction. The underground tanks and a former dry-cleaning business were the source of the pollution, he added.
"We found not just petroleum (contamination) but also metals and PCBs," Clarke said.
On the positive side of the equation, the rest of the soil excavated for the tunnel has been found to be a sandy material that can be reused on the project. Only about 10,000 cubic yards of fill will be required, McBride said.
The first phase of the tunnel required a 30-foot-deep cut 500 feet long. A shotcrete shoring system was used here, McBride said. Material was removed by excavators in 5-foot lifts and carried to the far end of the site by articulated hauler for storage or removal. Soil nails with 30-foot tie-backs were installed, the wall was shot, and then the excavators came back in to restart the process.
Three different shoring systems are being used on the second phase, due to varying space limitations at the street level: beams with tiebacks, beams with struts, and open cut with 1.5-to-1 slope. Work on this phase began May 5, McBride said.
The concrete box structures that make up the tunnel are poured in place. The contractor brought several suggestions to this element of the project, Clarke said.
"Waterproofing the tunnel was a difficult challenge," he said. WSDOT had found a vendor to supply an admixture to the concrete, but Tri-State suggested an alternative product, Xypex, that was not only self-sealing but also less expensive than the other choice.
Similarly, it was Tri-State's idea to use concrete form liners inside the tunnel that would create relief patterns on the walls. WSDOT had originally planned to pattern the walls but later dropped the idea to reduce costs, Clarke said. But Tri-State was able to reuse the form liners from a previous project to hold down costs. Some of the walls have a tree-silhouette pattern, while others mimic the look of basalt.
"The city is pretty pleased," McBride noted.
Effective Water Treatment
An even bigger contribution by Tri-State Construction was the innovative water treatment system employed for the project. With runoff pollution being a major environmental issue for construction project these days, the contractor has come up with a seven-tank system that includes three stages of filtering, McBride said.
The project plan called for discharging treated runoff water into the city's sanitary system for disposal.
"We had to assume the water would be bad," McBride said, "but during design it wasn't anticipated that we would need such a substantial system."
The Tri-State system, designed by Water Techtonics, is smaller and more efficient than the one WSDOT originally envisioned using. Water is treated with caustic in the first four tanks to knock out heavy metals and then injected with chitosan in tanks 5 and 6 for turbidity. In the process, it passes through a sand filter, a hurricane filter and a carbon filter.
The system runs 24 hours a day, seven days a week, with four operators working alternating shifts. The volume is 160,000 gallons per day, McBride said. But most importantly, the system works.
"All the tests have come in clean," Clarke said. "It's kind of a thing of the future. This is going to become the system on a typical WSDOT job now."
As might be expected considering the foregoing, a spirit of cooperation and teamwork pervades the project. McBride and Clarke hold weekly meetings to work out issues as they go.
"It's not a design-build project, has a partnership feel to it," McBride observed. "The machine never stops."
Partly as a result, the project is now on schedule despite the time lost during the first phase due to the contaminated soil. By resequencing the work, instituting an overtime work schedule, bringing in an extra crane, and establishing a detour earlier than planned, the team has been able to pick up the month that was lost.
The safety record also has benefited, with just one reportable accident recorded in nearly a year of work.
"At the start of the job, public and employee safety was our biggest concern," McBride recalled. Tri-State has used a relatively large number of flaggers to help keep pedestrians and motorists out of harm's way in the work zone. In addition, the project completely shuts down daily while the shipyard is on its lunch break.
Once the tunnel is complete, the contractor will finish the project by re-establishing Burwell Street and Pacific Avenue on top of it. A separate project by the city of Bremerton will create a 50-foot-wide park along one side of the site, Clarke said.
"It's a good job going well," he added.