Collaboration between the U.S. Army Engineer Research and Development Center (ERDC) and the U.S. Army Corps of Engineers (USACE) New Orleans District is a critical step in ensuring the stability of vital infrastructure. ERDC is assisting the district in inspecting the dewatered bays for voids beneath the Old River Low Sill Structure, located about 25 miles south of Vidalia, Louisiana, as part of the Old River Control Complex.
Built in 1959, the 566-foot-long concrete structure is founded on steel piles. The structure’s foundation was previously affected by a large scour during the 1973 flood, when an eddy current washed away part of the area beneath it and one of its wing walls. To remediate, the scoured region was filled with rock and grout.
Recently, ERDC conducted microgravity surveys to assess the status of this past scour, using a method that overcomes interference from the steel piles, which had hindered previous geophysical inspections.
“The bays were dewatered for maintenance purposes. The structure was built in the late 1950s, and the gate rails needed inspection and repair, along with other maintenance activities,” said Rebekah Lee, a research geophysicist at ERDC. “While we had conducted several geophysical surveys around the structure before, imaging directly beneath it was difficult due to the steel beams below.”
The dewatering of the bays provided a rare opportunity to use geophysical equipment directly over areas of both scour and non-scour. Because traditional methods were limited by the steel piles, microgravity was selected as the most viable alternative.
“We surveyed one bay that was unaffected by scour and two bays that were,” said Lee. “The bay without scour serves as our baseline. If there’s a void, we should see a low point in the gravity readings, due to the lack of mass in that area.”
By comparing data from the scoured bays to the stable baseline, the team can detect potential voids beneath the structure. The results from the microgravity surveys of bays 8 and 9 will be compared to the baseline bay 4 to evaluate the condition of the remediated scour. The data from these surveys is still being processed.
This collaboration is crucial for understanding the overall stability of the structure and will guide future USACE maintenance efforts.