Tidal Influence on Embankment Settlement in Coastal Louisiana

The existing Louisiana Highway 1 (LA-1) runs along the bank of Bayou LaFourche in the coastal region of Louisiana and is a primary two-lane transportation route for foreign oil offloaded from ships in the Gulf of Mexico. The Louisiana Department of Transportation and Development (LADOTD) decided to upgrade the southern 28 km portion to a four-lane, fully access controlled, elevated bridge. Earthen embankments link the North and South Connectors to the existing roadway. These embankments would have fill heights of 0.6 m to slightly over 2 meters. Even with relatively low embankment heights, consolidation settlements of 46 cm to 150 cm were predicted. In order to meet the residual settlement requirement, a combination of wick drains, lightweight aggregate fill, and surcharges was used to reduce and accelerate the settlement. Vibrating wire settlement monitoring cells were used to measure the progress of settlement. Observations made from the settlement measurements indicate a strong tidal influence on the settlement behavior of the embankments. This paper presents the observed tidal impact to the settlement and the resulting difficulties associated with evaluation of the settlement data. Both Asaoka and hyperbolic curve matching methods were used to predict the final settlement values. The two methods produced comparable estimated final settlement values.