Lessons Learned from Levee Embankment Tie-In Construction in Marsh Environment

This case study describes the results of a monitoring program conducted during the construction of a preload and final levee tie-in embankment in Terrebonne Parish, Louisiana. The overall project included a floodgate, floodwall, and a levee embankment tie-in situated within the Louisiana Gulf Coastal Plain. Site exploration revealed thick deposits of very soft clay with layers of organic clay and peats. In general, near surface soils were very soft and compressible. Due to subsurface conditions, achieving sufficient settlement during the construction of the tie-in through a ground improvement program was essential to reduce the negative impact of drag settlement on structural features installed at the end of the preload. Geotechnical instrumentation of the levee tie-in comprised of settlement plates, settlement gauges, magnet extensometers, and piezometers. The monitoring program was conducted to assess rates and magnitudes of settlement for the levee tie-in and effectiveness of the prefabricated vertical drains (PVDs). Piezometric data was used to monitor pore water pressure response to the addition of fill and the dissipation of pore water pressure in the months after fill placement. This study presents the results of the instrumentation and monitoring program as well as key lessons learned.