West Sacramento River Levee Improvement Project
History
Historical records and recent investigations of the levee at this site indicated that the material used to build the original levee consisted of permeable sand dredged from the Sacramento River. Dredging of the River was commonplace after the Gold Rush, because mining activities in the Sierra Nevada discharged large volumes of sediments to the Sacramento River and tributary creeks and streams. These sediments accumulated in those streams and caused water levels to rise, leading to frequent flooding problems.
Subsurface Conditions
The subsurface conditions were generalized for seepage and stability analyses. The levee embankment core was modeled as non-plastic silt with the waterside modeled as clean sand fill. The soil foundation beneath the levee prism consisted of a moderately firm clay blanket layer underlain by silty sand and sandy silt (this layer was modeled as silty sand for seepage analysis). The basement layer of the model consisted of firm hard clay.
Early Implementation Project (EIP) Phase I
Due to the late award of the contract Raito commenced the test section late in the season, consequently production had an extremely truncated schedule to complete the cutoff wall in time for the levee to be rebuilt back to flood height before the end of the season.
The "two pass" method adopted in Phase I of the Marysville project was initially considered to meet the specified minimum wall width of 36 inches. A Value Engineering Change Proposal however was accepted saving money and more importantly time in the already restrictive schedule that allowed for the "one pass' method to be used.
The project was situated west of the Sacramento River and adjacent to residential areas in West Sacramento; and the 2,950LF cutoff wall was completed with minimal disruption to the residents because of the low noise and very little vibration produced by the drill rigs. All tests passed for strength and permeability before or at the specified 28 days.
The Sacramento River Flood Control System includes dams and reservoirs, levees, weirs, bypasses, and other features built over the last 150 years. Approximately 980 miles of levees in this complex system protect urban and rural areas within the Sacramento River Watershed of 27,100 square mile from frequent flooding, and have prevented billions of dollars in damages. Raito is proud to be part of these levee reinforcing and restoration programs.
Project Highlights
- Deep Soil Mixing (DSM) was used for ground water cutoff incorporating Soil-Cement-Bentonite (SCB) wall sonstruction method.
- Triple-axle DSM equipment was used to depths up to 135 feet. Two DSM mixing rigs were used on a double shift system.
- Installation of cut-off wall was completed on time within a very tight schedule.
- DSM construction fulfilled requirements for Unconfined Compressive Strength in 28 days to be not less than 40 psi and a maximum of 200 psi.
- DSM construction exceeded requirements for Hydraulic Conductivity of 1x10-6 cm/sec maximum.
- Raito was responsible for the design of the trial mix.