Nisqually River Trestle Flood Damage Repairs Design
City of Tacoma
Elbe, Washington
The City of Tacoma’s railroad, the Tacoma Rail Mountain Division Line, sustained damage in several locations in the November floods near Elbe, Washington. Exeltech performed a field assessment, structural inspection, and conceptual-level engineering analysis Type, Size, and Location (TS&L) study with three alternatives for the replacement of the storm-damaged Nisqually River Trestle. The preliminary TS&L concluded that both end abutments would require replacement regardless of the bridging option selected. Both single-span and multi-span options using steel and concrete material sections were considered, as well as open-deck and ballasted-deck solutions. Three of the most cost-effective bridge alternatives were analyzed.
Exeltech performed conceptual engineering for the three preferred options using in-house railroad bridge design tools and the American Railway Engineering and Maintenance-of-Way Association (AREMA) design criteria. Our design loading utilized a Cooper E 80 live load with impact for diesel locomotives. Cost estimates were developed for each of the three alternatives considered. The estimates were based on unit costs from WSDOT’s Bridge Design Manual and from contractors listed on the National Railroad Construction and Maintenance Association website. After applying a decision matrix to all three alternatives, alternative three (two spans of steel plate girders) was selected as the preferred alternative because of its reasonable relative cost, its ability to create the best hydraulic solution, and because it had the fewest environmental permitting issues. Exeltech completed the final design and prepared the construction plans, specifications, and estimates for construction bids.
Exeltech led the environmental compliance process and facilitated agency and design team coordination to streamline environmental permitting. The project constructed two new spans and abutments at each end of the bridge, requiring over 1,500 cubic yards of riprap fill in the Nisqually River. The project was permitted under the streamlined Nationwide Permit Program due to early coordination with the US Army Corps of Engineers.