American River Watershed
- Location: Sacramento, CA
- Owner: U.S. Army Corps of Engineers, Sacramento District
- Technique(s) Utilized: Cement-Bentonite Cutoff Wall
Background
The excavating was done with long-reach
hydraulic excavators, using cement-bentonite. The trench was cut through the existing earthfill levees. The geology was sand and gravel, fine silty sand, and clays. In order to strengthen the levees for flood events, the barrier was extended into an impervious stratum or deep enough to reduce the hydraulic gradient under the cutoff. The average depth of the cutoff was 20 meters. The material used for this 600 mm thick barrier had to be flexible and strong, and impermeable. The contract specified a 28-day unconfined compressive strength of between 15 and 300 psi and a permeability of less than 5 x 10-7 cm/s.
The requirement of keeping the levee crest road open
to traffic during the project was a major constraint on
this section. Construction of the cement-bentonite barrier, 1000 meters long, lasted from October to December 1999, using a single trenching machine. The compact bentonite cement mixing plant was located on the side of the road. Slag cement was used for the bentonite cement mix. Tests revealed a 28-day permeability of the order of 5 x 10-8 cm/s and a 28-day unconfined compressive strength of 150 psi.
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