Salton Sea Preliminary In-Sea Geotechnical Investigation

SECTIONSIXPreliminary Embankment Design ConsiderationsSandy alluvial deposits were encountered near the seafloor in some of the explorations near the existingshoreline (see logs of Borings 7, 11 and CPTs 9, 10, 12, 23, 25). Five to ten feet of fine-grained seaflooror lacustrine deposits typically overly the sand. It would appear that the most promising areas for a sandborrow source would be along the west side of the Sea, or near the mouth of Salt Creek along the eastside. It is suspected that the steeper bathymetry in these areas is indicative of a predominately sandymaterial near the surface. Particle size analyses on samples obtained from the sand layers encounteredindicate they are fine sands with less than 20 percent silts and clays, but may be interbedded withmaterials with higher fines content. Ideally, it would be desirable to use coarser-grained sands and gravelsthan those encountered in this investigation that would drain and gain strength quicker when hydraulicallyplaced. A compilation of the particle size analyses on the alluvial sands are presented in Figure 24.The alluvial sand layer encountered in Boring 7 was about 20 feet thick. This layer would need to extendover about 1,000 acres (or about 1½ square miles) to provide the borrow for the 32 million cubic yards ofmaterial that was estimated for a hydraulically placed earthen barrier.W:\27663042\00005-c-r.doc\1-Mar-04\SDG 6-5