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GEOTECHNICAL CONSTRUCTION American River Watershed Project Construction of 540,510 square feet soil-cement-bentonite cutoff wall to a depth of 70 feet. The cutoff wall with a maximum permeability of 5x10-7 cm/sec and an average unconfined compressive strength of 40 psi protects the stability of an existing levee by providing isolation of river water seeping into the levee and its foundation soils. The cutoff wall was constructed during the period August 29, 1998 to October 29, 1998 (9 weeks). Four large excavators capable of excavating to maximum depth of 80 feet were used. In order to meet the tight schedule and performance requirements, Geo-Con designed a backfill mix that met the specified 28 day permeability requirement after only 5 days.
Jet grouting was specified in several areas under active overhead utilities with limited clearance. In lieu of jet grouting, Geo-Con value-engineered an alternative which consisted of excavation to a depth of 70 feet at these locations. This eliminated expensive pre-construction testing of jet grouting, provided a quality final product and saved the Owner and the general contractor approximately $800,000
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