Seattle Ferry Terminal at Colman Dock

Our team was responsible for replacing Colman Dock’s timber trestle, main terminal building, Slip 3, overhead loading structures and the passenger-only ferry facility. The project reconfigured the dock layout for safer and more efficient operations and addresses existing safety concerns related to vehicles and pedestrian traffic.

We provided technical direction during construction, as well as assembly, outfitting and management of a multidisciplinary team that included structural, civil, architecture, plumbing, building and marine electrical, building and marine mechanical, wayfinding, digital messaging, hazardous materials and landscape architecture.

The team successfully reduced construction costs of the trestle pile foundation structures by more than $15 million from the preliminary design, enabling the project to fit within budget. This foundation supported the driving deck and multiple buildings, such as the terminal building, which maintained two stories of clearance above the driving deck.

Seismic Safeguards

The project uses of 8.82 acres of concrete trestle, with structures that include a main terminal building, an entry building with retail space, an elevated walkway between the terminal building and the passenger-only ferry, and an overhead passenger walkway on the northernmost slip. There is a new bicycle entry and holding area, plus stairs connecting the facility to Alaskan Way, a major thoroughfare along Elliott Bay waterfront. These structures are supported on steel pipe piles that are 36 inches in diameter.

Colman Dock is in a high seismic zone. The offshore site is underlain by non-liquefiable soft silt, which is overlying liquefiable silt, which in turn overlays glacial soils. The main geotechnical and structural challenge is lateral instability of soils above the glacial soils and the consequential impact on the driven pipe piles and drilled shafts.

The optimized project design used advanced soil-structure interaction analyses, which facilitated shorter pile embedment into glacial soils. To both protect the piles’ capacity and increase the structure’s seismic response period, seismic-induced bending moments were developed between piles and precast deck elements.

“These resiliency measures are in accordance with earthquake and seismic load standards of the American Association of State Highway and Transportation Officials and International Building Code,” Wray said.

More than 750 total precast panels and 536 unique panels were used to overcome key design challenges. Using Revit 3D building information modeling software, engineers and contractors coordinated and located where the penetration and hanging loads were needed for utilities.

Precast panels helped solve this challenge and addressed concerns regarding construction, such as impacting traffic on major roadways and potential concrete spills into the water, according to Patty Rubstello, PE, senior vice president and national transportation strategic advisor at WSP in the U.S.

Phasing Solutions

The project employed a general contractor/construction manager procurement method because of complex construction phasing required to maintain Colman Dock’s operations. Only one of the three slips could be taken out of service at any given time, so extensive phasing plans were developed to keep the busy terminal operating during construction.

“Rapid construction was not the main goal. Rather, the higher priority was rapid construction of phases,” Wray said. “We needed rapid local installation zones to complete specific phasing items so that traffic patterns could switch from ‘soon to be demoed areas’ to ‘newly completed areas.’ This allowed the terminal to stay open and functional during construction.”