The BA-171 project involved the creation or nourishment of over 900 acres of back-barrier marsh using hydraulically dredged and placed material from a borrow area approximately 1.5 miles offshore in the Gulf of Mexico. The fill area was fully confined with earthen containment dikes (ECDs) along the west, north, and east sides, and to the south by the previously constructed Caminada beach and dune projects (BA-0045 and BA-00143). Due to the length of the project, the marsh creation area was divided into increments by smaller, “training” dikes to promote the proper distribution of sediment.
Sigma Consulting Group provided Supervision and Inspection Services as a prime consultant to CPRA. AME was a sub-consultant to Sigma and provided geotechnical instrumentation and monitoring services.
A full-scale Geotechnical Instrumentation and Monitoring Program was developed and executed during the construction phase of BA-171.
The first phase of the program included probing and vibracore collection in a priority section of the earthen containment dike that was designed to have sand to be based-in to achieve the factors of safety. The analyses conducted by AME’s team members allowed for the removal of this sand and a change order reducing the construction contract by approximately $350,000.
The second phase included instrumentation being installed pre-construction to monitor several weaker sections of the dike to determine the wait time needed between lifts. After data was collected and analyzed, wait times between lifts were reduced from the design time of 45 days to 14 days, which allowed the Contractor to continuously work within one increment.
The third and final phase included the installation of 17 Instrumented Settlement Plates (ISPs). AME was able to inform the Owner of areas where excess fill was being placed by reducing the data collected by the instrumentation. This data was recorded in real-time and alerts were sent which indicated the height of the fill as well as the density, or amount of solids. Additionally, cameras were installed in each increment of the project, which multiple times informed the Owner that slurry was approaching over-topping the earthen containment dikes.
The Local Sponsor of the project is CPRA and the Federal Sponsor is EPA.