ST. MARY PARISH, LOUISIANA
Eustis Engineering performed an extensive geotechnical exploration to support the design of earthen and structural systems that would collectively be used to provide flood protection to the project area. St. Mary Parish plans to phase the entire project into four construction contracts. Phase 1 is dredging and material placement along the south bank of Bayou Chene and Tabor Canal. Phases 2 and 3 are the construction of the Bayou Chene floodgate and adjacent floodwalls. Phase 4 comprises earthen levee embankment construction along Avoca Road and Avoca Island.
Our field explorations in 2012 and 2013 were comprised of 74 soil borings (both 3 and 5-in. diameter), 38 cone penetration tests, and 32 auger borings to assess subsoil stratification at the project site. Soil mechanics laboratory tests were performed in our in-house laboratory to evaluate the physical properties of the substrata.
Eustis Engineering developed preliminary design recommendations for this project in 2012 and 2013 in accordance with the U.S. Army Corps of Engineers’ Hurricane and Strom Damage Risk Reduction Design Guidelines. Since completing the geotechnical investigations, a new set of geotechnical guidelines was issued by the State of Louisiana, Coastal Protection and Restoration Authority entitled Louisiana Flood Protection Design Guidelines. Therefore, engineering analyses associated with this project reflect both design guidelines.
The focus of Phase 1 is to dredge the Bayou Chene channel bottom and excavate the side slopes of Bayou Chene. The material will be placed along the south bank of Bayou Chene and west bank of Tabor Canal to serve as a bridge lift for a future levee section. To establish acceptable design slopes and dimensions near dredge locations, Eustis Engineering performed analyses with earthen levees (for Phase 4) adjacent to slopes in order to understand necessary setbacks between the cut slopes and earthen levees. Engineering analyses concentrated on settlement and levee overbuild estimates, deep-seated global stability analyses, and construction recommendations.
The focus of Phases 2 and 3 is the design and construction of a barge flood gate and adjoining braced “A-Frame” steel sheet pile floodwalls within Bayou Chene and a tidal control structure within Tabor Canal. Analyses have included deep-seated global stability analyses for the floodgate structure, seepage and piping analyses, estimates of axial pile load capacities, and horizontal soil reaction as well as lateral pile deflection relationships.