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Structures Technical Presentation: Brine Flies and Boxcars: Building a New Bridge on the Great Salt Lake Causeway (Room Sagamore Ballroom 3-5)

The Union Pacific Railroad’s 24-mile causeway across the Great Salt Lake outside of Ogden, Utah, is a vital link in the transcontinental railroad, carrying dozens of trains per day. Built in 1900, the causeway is located in a harsh physical environment—with salinity twice as high as normal seawater, temperature extremes, brine flies that clog air filters, and extremely soft soils leading to feet of settlement per year. Finally, it became necessary to replace two aging concrete culverts that had allowed water to flow through the causeway. The decisions regarding the location of the replacement bridge and its design were based on sophisticated engineering modeling and knowledge of the complex geology and geotechnical characteristics of the causeway and the lake sediments. The constraints of limited site access, track time, and staging areas, as well as environmental permit restrictions, had to be considered during planning, design, and construction of the culvert replacement. The requirement to maintain train passage through the construction site necessitated carefully sequenced construction using a temporary shoofly. Pile placement was complicated by the need to predrill and case holes before driving and encountering corroded old box cars. The rock, used for armoring protection and hydraulic flow management, required specific size and durability characteristics that limited the sources from which it could be quarried. The requirement for accurate placement of the rock was addressed by the contractor’s use of machinery equipped with state-of-the-art GPS surveying equipment. The project was successfully completed in December 2016.