A finite element analysis was used to examine the lateral soil deformation behavior of soft soils during the construction of levee improvements along the Sacramento River East Levee (SREL) in the Natomas Basin just north of Sacramento, CA. After Hurricane Katrina in 2005, it was found that Sacramento had the greatest risk of flooding due the ageing and inadequately maintained levee systems. An executive order was declared and agencies began to evaluate and mitigate levee conditions. Sacramento Area Flood Control Agency (SAFCA) evaluated the levee conditions and then designed and executed levee improvements along a 10 mile stretch of the SREL from 2005-2011. To meet United States Army Corps of Engineers Standards, a new adjacent levee was required. For underseepage control for much of this length, a soil-bentonite cutoff wall (SB wall) under the future adjacent levee crest was to be excavated near the toe of the existing 2H:1V embankment. Prior to construction, inclinometers were installed at the adjacent levee toe and between the existing levee and slurry trench. Inclinometer data showed unexpected horizontal movements of up to 10 mm, away from the trench during the excavation under a bentonite-slurry mixture. After the soil-bentonite fill was placed, horizontal movements shifted towards the trench and greater than 25 mm of movement were observed to distances nearly two times the slurry trench depth from the cutoff wall alignment.

A study was developed to evaluate the key parameters affecting lateral deformation of the soft Sacramento River soils. The model was implemented in multiple steps to mimic the actual phased construction performed in the field. The steps included the initial working platform fill, excavation and subsequent filling of the trench with bentonite-slurry mixture, backfilling of the trench and final filling of the embankment. Soil and ground conditions in the model were established from field and laboratory testing. Developing accurate stress-strain response was crucial to understanding the key parameters attributing to the lateral movement in the field. Results obtained in the model were compared with recorded field measurements determined from inclinometer readings. The initial movement away from the trench was likely dependent on stiffness of the natural deposits. The amount and rate of lateral movement toward the trench, after backfilling, trended with horizontal consolidation of the soil-bentonite backfill. This study can be useful in understanding the lateral behavior of the soft soils for making lateral deformation predictions in the case of construction excavations.