BRINE FUES AND BOXCARS: BUILDING A NEW BRIDGE ON THE GREAT SALT LAKE CAUSEWAY

摘要

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 seven times higher than normal seawater, temperature extremes, brine flies so thick that they clog air filters, and extremely soft soils leading to settlement each year that is measured in feet rather than inches. 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 bridge to replace the culverts 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 the discovery of old corroded boxcars. 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.