Modjeski & Masters Engineering
Underwater Acoustic Imaging
Fenstermaker conducted the first underwater inspection of the Huey P. Long Bridge since its inception in 1935. The bridge spans the Mississippi River in New Orleans, LA, and was set to undergo a major expansion requiring extensive modification to the upper section of the bridge piers. A detailed inspection to establish a baseline of the structure’s existing condition was needed before the expansion project could commence. Commissioned to evaluate and record the condition of the bridge piers using Underwater Acoustic Imaging technology, Fenstermaker was hired as a sub-consultant to Modjeski & Masters Engineering to complete the investigation.
Fenstermaker performed an acoustic imagery visualization of the four bridge piers, including both sides of the piers and their upstream and downstream noses. The inspection was accomplished by deploying a set of Kongsberg-Mesotech steered beam sonar/profilers from a barge platform positioned along each face of the piers. A rotating tower mechanism, designed and manned by Fenstermaker, was used to guide the sensors to the necessary depth and direct the acoustic scan patterns while maintaining the stability necessary for high-resolution imaging in a severe water current environment.
The high definition acoustic visualization allowed observations of the bridge piers and support caissons with an added capability of distinguishing the grout seams between the granite armoring on the upper section of the piers. The water depth at the piers varied from 36 to 98 feet, requiring different deployment elevations at each respective pier. The entire inspection was completed in five days with two additional days for mobilization. The information gathered served dual purposes for the Louisiana Department of Transportation and Development. First, the surveys confirmed the condition of the piers, establishing an objective record indicating that the piers were in very good condition. Second, the recorded sonar data and translated image visualization served as reference of the piers, which was vital in planning the extensive bridge expansion project. Fenstermaker’s underwater acoustic imaging played an important role in the project’s construction management and QA/QC phase.
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