Construction of Mixed-in-Place Cutoff Wall for Levee Strengthening Program

Floods have had devastating effects on life, property, and the economic prosperity of the Sacramento area. The most recent significant floods in the Central Valley (including Sacramento), which occurred in 1986 and 1997, together caused over $1 billion in damage (U.S. Army Corps of Engineers, 1997). Additional flood control measures will be required to protect the urban areas of the Central Valley which has the highest flood risk in the nation.
Most levees in the Central Valley were constructed in the early part of the twentieth century using sands, silts, clays, and organic soils, often poorly compacted over permeable foundations. Local farmers reclaimed flood plains by using dredged materials within the river channel to create these levees. The levees were constructed to foster economic development and promote public safety. However, the noted materials are not adequate to support the levees and its foundations during a major flood event, as water tends to seep through and under levees. If seepage is serious, boils may occur on the landside carrying some of the levee material with it which may cause levee failure and flooding.
The West Sacramento Flood Control Agency has recently implemented a levee-strengthening program along the banks of the Sacramento, California, including the I Street Bridge site (2008), Sacramento Bypass/CHP Academy (2011) and the Rivers Phase 1 (2011).
This paper describes a case study on the Rivers Phase 1 project including design, construction and performance of an underground mixed-in-place cutoff wall within a 3,000 feet long levee segment located along the right bank of the Sacramento River. The cutoff wall was constructed using the multi-auger deep soil mixing in order to reach the maximum design depth of 135 feet in a residential area with severe space and access limitations.