No abstract

This paper discusses the use of various technologies and advanced computational modeling techniques that were combined for monitoring the performance of pier riprap on the basis of a field case study-Pier 3 of a bridge over the Middle Fork Feather River-in northern California, USA. The first phase involved capturing the field condition of the bridge site using sonar instrumentation technology in order to obtain high resolution bathymetry data. The second phase entailed enhancement and transformation of the scanned bathymetric data into a 3D CAD model to be used as the initial geometry for numerical modeling. A Fluid Structure Interaction (FSI) numerical approach was applied to simulate the rock incipient motion i.e. shear failure by coupling Computational Fluid Dynamics (CFD) software STAR-CCM+ and a Computational Structural Mechanics (CSM) software LS-DYNA. Several coupled simulations have been performed with varying flow conditions to identify shear failure conditions for the riprap apron.

The database from flume experiments focused on the performance of riprap layouts based on field installations and FHWA HEC-23 design guidelines against clear-water abutment scour combined with Computational Fluid Dynamics (CFD) is used to investigate how flow fields at single span bridge openings, dominated by flow contraction, adjust in response to variations of bed roughness and cross-section geometry due to riprap installations. These adjustments increase bed shear stress magnitudes on the unprotected erodible bed leading to underestimated contraction scour depths therefore creating instability, and ultimately causing edge failure of the riprap. Based on the combined physical/numerical modeling approach an edge failureresistant riprap layout is proposed. Furthermore, the CFD approach provides an insight into shear stress magnitudes within a nonuniform bed roughness in the bridge opening, and a comprehensive flowdepth-riprap interaction model to define limits for "hydraulically narrow" bridge openings that might be prone to edge failure of the scour protecting riprap.