Mitigation of Unforeseen Subsurface Conditions through Geotechnical and Structural Collaboration

The 740ft Swing Bridge in Katharyn, KY was originally constructed in 1905 with a 338ft center-pinned swing truss carrying a single track. The swing truss was fixed in place in the 1940’s. The bridge was selected for replacement due to significant deterioration of the bridge, the pin connections, and the members. The selected alternate was four deck-girder spans, which adds two concrete piers in the Salt River waterway. While attempting to install the northern pier pile foundation, a debris field consisting of stones, concrete, and other materials was discovered. After evaluating the results of a preliminary investigation and excavation, it is believed that the original pivot pier had collapsed during a flood event shortly after construction and was abandoned to the river. A new pier was then simply built on top of the remains. A reassessment of the alternates and additional geotechnical exploration indicated that the traditional pile foundation should be replaced with a micro-pile system that penetrates the debris field. Thus, the original pier location and superstructure layout were maintained. The presentation includes a project overview and then focusses on the debris field discovery, the foundation redesign including impacts of obstructions, and final construction of the bridge. All analysis and design were completed according to the current applicable edition of the American Railway Engineering and Maintenance-of-Way Association, Chapters 8 - Concrete Structures, and Chapter 15 - Steel Structures.