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Posted 13 December 2012
Neither bridge nor tunnel, the new Port of Vancouver USA rail trench is a bit of both. The Port is situated along the Columbia River, which serves as a border between Washington State and Oregon, and is the largest river in the Pacific Northwest. When mile-long unit trains enter or leave the Port using the north/south line, the east/west-running mainline is blocked and other rail traffic is significantly delayed. A new rail entrance was needed for the unit train traffic that would eliminate the blockage.
The only feasible alignment for the new line is along the north bank of the Columbia River and beneath an existing low clearance BNSF Railway bridge that carries the north/south mainline across the river. An approximately 1,350-foot portion of the new mile-long track segment will be carried by a partially elevated reinforced concrete structure or “trench” that will protect the rail from 100-year flood waters and also support the rail line along the irregular river bank.
To resist flooding and to provide the required clearance under the existing BNSF bridge, the continuous concrete trench was selected as the preferred solution. Closely spaced batter piles support 1,100 feet of the trench and provide resistance to seismic loads and buoyancy when the river level is above the trench bottom.
Portions of the rail trench will be constructed below the U.S. Army Corps of Engineers’ ordinary high water mark and will be subjected to timing restrictions on in-water work. The river is home to several species listed under the Endangered Species Act, and the Port has undertaken a low-impact approach to construction: no work will be conducted in the flowing water of the river. This has necessitated careful planning and sequencing of the work that takes projected river levels and tidal fluctuations into account. Other challenges include an extremely constricted site with limited access and the need to minimize impacts to adjacent tenants and their operations.
Construction began in summer 2012; when the trench is complete in 2015, this unique facility will meet the latest structural, seismic, and environmental requirements and maximize the Port’s operational efficiency.