BAYOU CHENE FLOOD CONTROL STRUCTURE
Eustis Engineering L.L.C. 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 planned to phase the entire project into four construction contracts. Phase 1 was dredging and material placement along the south bank of Bayou Chene and Tabor Canal. Phases 2 and 3 were the construction of the Bayou Chene floodgate and adjacent floodwalls. Phase 4 comprised earthen levee embankment construction along Avoca Road and Avoca Island.
Our field explorations in 2012 and 2013 comprised 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 explorations, 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 was to dredge the Bayou Chene channel bottom and excavate the side slopes of Bayou Chene. Material was 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 (for Phase 4), Eustis Engineering performed analyses with earthen levees adjacent to slopes to determine 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 were design and construction of a barge flood gate, adjoining braced “Plumb & Batter” steel sheetpile floodwalls within Bayou Chene, and a tidal control structure within Tabor Canal. We performed deep-seated global stability analyses for the floodgate structure, seepage and piping analyses, and estimates of axial pile load capacity and developed site-specific p-y curves for various sizes of open-end steel pipe piles that led to over $1 million in savings for the project!
Phase 4 comprised earthen levee embankment construction along Avoca Road and Avoca Island. During Phase 4B, Eustis Engineering sampled the bridge lift material (33 hand borings taken through the bridge lift, each to a depth of 4 feet), tested the soil in our laboratory (visual classification, natural water content, percent organics, particle size distribution, and Atterberg limits determinations), and developed new estimates of potential levee settlement based on the current, expedited construction schedule. Engineering During Construction efforts included project submittal and RFI reviews along with development and execution of a dynamic pile test program to substantiate the use of 2.5 as the foundation design safety factor.