United States Department of Transportation
i
NextScour Case Study: The Lafayette Avenue Bridge Over the Saginaw River in Bay City, Michigan
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2023-01-01
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[PDF-2.72 MB]
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Edition:Research Report
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Abstract:The Michigan Department of Transportation (MDOT) plans to replace the Lafayette Avenue Bridge over the Saginaw River in Bay City, MI. Hydraulic scour analysis of the planned bridge replacement resulted in deep scour depths, which MDOT believed were excessive due to a subsurface layer of cohesive soil that existed across the bridge site. MDOT reached out to the Federal Highway Administration (FHWA) to inquire if FHWA’s NextScour Research Initiative could potentially reduce the scour design depths. Additionally, both the existing bridge and proposed bridge replacement featured large bascule piers, and MDOT asked if FHWA could conduct physical modeling of the piers in their flume to study scour formations around the piers. Through a Transportation Pooled Fund study, TPF-5(461), FHWA was able to perform five tasks for MDOT that are summarized in this report (FHWA 2020). Task 1: Perform hydraulic modeling of the site to obtain flow velocities and bed shear stresses. Task 2: Perform soil erosion testing on the cohesive soil to determine the clay’s critical shear stress. Task 3: Develop decay functions to establish the relation between hydraulic loads and depth. Task 4: Conduct computational fluid dynamics scour modeling in sand and clay soils. Task 5: Conduct a probabilistic scour analysis to quantify the risk levels for the various scour analysis methods. This research study showed that the cohesive layer of clay at the site could potentially stop the scour at this bridge site, and the NextScour methodology is a developing tool to improve accuracy for bridge foundation design.
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