Three-Dimensional Simulation of Bridge Foundation Scour on Mississippi River Bridges 9321 & 27801

Abstract

We present data-driven numerical simulations of 100- and 500-year floods events in the Mississippi River at its intersection with the Highway I-694 by coupling coherent-structure resolving hydrodynamics with bed morphodynamics under live-bed conditions. The study area is about 1.7 miles long and 220 yard wide reach of the Upper Mississippi River, near Minneapolis MN, which contains several natural islands and man-made hydraulic structures. We employ the large-eddy simulation (LES) and bed-morphodynamic modules of the Virtual Flow Simulator (VFS-Rivers) model, a recently developed in-house code, to investigate the flow and bed evolution of the river along the reach and near the bridge piers BR 27801 and BR 932. We integrate data from airborne Light Detection and Ranging (LiDAR), sub-aqueous sonar apparatus on-board a boat and total station survey to construct a digital elevation model of the river bathymetry and surrounding flood plain, including islands and bridge piers. A field campaign under base-flow condition is also carried out to collect mean flow measurements via Acoustic Doppler Current Profiler (ADCP) to validate the hydrodynamic module of the VFS-Rivers model. Our simulation results for the bed evolution of the river under the 100- and 500-year flood reveal complex sediment transport dynamics near the bridge piers consisting of both scour and refilling events due to the continuous passage of sand dunes. A brief description of the findings in terms of maximum scour depth around individual bridge piers can be found in the executive summary of the report.