Innovative Bridge Foundations Reduce Track Outage - BNSF Bellefontaine Bridge, Bellefontaine, Missouri

摘要

The Bellefontaine Bridge was constructed over the Missouri River over 100 years ago and is still in use despite its long life. BNSF Railway placed the bridge on the capital replacement list for 2014-2015. A new bridge would have to be constructed along the same alignment as the existing structure because of environmental permitting and the proximity of another bridge that had been built directly to its south. Keeping an existing bridge in service during creation of a new structure—in a fairly tight right-of-way constrained by wetlands and the DOT structure—would have been challenging enough. In this case, the subsurface conditions, consisting of 50 to 60 feet of weak alluvial deposits overlying another 100 feet of dense sands down to the top of rock at 165 feet below grade, made the installation of new foundations for the structure even more difficult. The project team designed and built an innovative composite foundation consisting of large-diameter drilled shafts through the alluvial material, with micropiles socketed into sound bedrock. This foundation not only minimized costs, but also reduced the risk of movement of the existing shallow pile-supported bridge during construction of the foundations and substructure for the new bridge. The new structure was built beneath the existing bridge, and then short track windows were utilized to complete the superstructure. This paper discusses the design and construction of the foundation solution, as well as provides load test data.