Salton Sea Preliminary In-Sea Geotechnical Investigation

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SECTIONTWOPreliminary Geotechnical Investigation2.3 LABORATORY TESTINGSamples of the subsurface materials obtained from the borings were returned to a geotechnical laboratoryfor testing. A summary of the laboratory testing performed is included in Table 2 and discussed below. Adetailed description of the testing program, and the results of the testing, are presented on the boring logsand in Appendix C. The following sections summarize the testing performed.2.3.1 Index TestingIndex testing was performed on the samples to further characterize and classify the materials. The testingincluded water content (per ASTM D-4959), bulk densities, Atterberg limits (per ASTM D-4318), particle sizeanalyses (per ASTM D-422), percent passing the #200 sieve (per ASTM D-1140), pinhole dispersion analyses(per ASTM D-4647), and specific gravity tests (per ASTM D-854). A summary of the index testing isprovided in Table 3. Results of the index testing are presented on the boring logs and in Appendix C.Corrosivity testing was also performed on selected samples. A suite of tests including resistivity, electricconductivity and chemical analyses were performed. The results of these tests are presented in Table C-1in Appendix C.2.3.2 Strength TestingA preliminary evaluation of the shear strength of the soil samples was obtained during the field programby using a Torvane TM apparatus. Both Unconsolidated Undrained (UU) and Isotropically ConsolidatedUndrained (ICU) triaxial compression test were performed on selected samples. The UU samples wereconfined using a pressure similar to the existing overburden pressures at the sample depth. A set of threeICU tests were performed on three separate specimens extracted from the same or adjacent Shelby tubes;these specimens were consolidated at pressures ranging from near existing overburden to pressuresanticipated under embankment loads. The UU testing was performed in accordance with ASTM D-2850,the ICU testing was performed in accordance ASTM D-4767. A summary of the triaxial strength testingis provided in Tables 4 and 5; detailed results are provided in Appendix C.2.3.3 Consolidation TestingConsolidation tests were also performed on some of the samples. These consolidation tests wereperformed in accordance with ASTM D-2435. The results of the consolidation testing are summarized inTable 6. Detailed results from the consolidation tests are provided in Appendix C.W:\27663042\00005-c-r.doc\1-Mar-04\SDG 2-4
SECTIONTHREESite ConditionsSECTION 3SITE CONDITIONSKnowledge of the site conditions has been developed from a review of the area geology, the previousinvestigations within the Sea, the bathymetry and topography that was available, and the field andlaboratory programs undertaken for this preliminary geotechnical investigation.3.1 GEOLOGIC SETTINGThe Salton Sea currently occupies the lowest portion of the Salton Trough, a deep basin that representsthe structural extension of the Gulf of California into North America. The Trough is essentially a closedbasin, bounded by mountains within the Western Mojave Desert Province to the north, the Basin andRange Province to the east, and the Peninsular Range Batholith to the west. To the south, deltaic depositsof the Colorado River prevent marine inundation from the Gulf of California. A geologic map presentingthe surficial geology of the area surrounding the Sea is presented in Figure 6; a legend for the geologicmap is presented in Figure 7.3.1.1 StructureThe Salton Trough is a deep structural pull-apart basin characterized by high seismicity, high geothermalactivity, extensional tectonics, crustal thinning, and rapid sedimentation (Damiata et. al., 1986). The basinis bounded by major, northwest trending, strike slip faults and uplifted highlands of crystalline rock.Geophysical studies (Tarbet, 1951; Biehler et. al., 1964) suggest that upwards of 18,000 feet (3.4-miles)of sediment have accumulated in the Salton Trough since the Miocene epoch (Eberley and Standley,1978). The central portion of the valley is underlain by a 6 to 10-mile deep trough of sedimentary andmetasedimentary rocks (Fuis et. al., 1982).3.1.2 StratigraphyThe Salton Trough is a deep basin that has been filling with sediments since the Miocene epoch. Theoldest, basal sediments, are the coarse clastic materials of the Anza Formation that where shed off thesurrounding crystalline highlands. The Anza Formation outcrops at the surface along the margins of thebasin. Within the southern portion of the basin, the Anza Formation interfingers and is overlain by asequence of essentially continuous deposits including the Alverson volcanics, playa deposits of the FishCreek Gypsum, marine and non-marine sediments of the Split Mountain Formation, marine deposits ofthe Imperial Formation, terrestrial deposits of the Palm Springs Formation, the Canebrake Conglomerate,and the subsequent alluvial and terrace deposits of Quaternary age. The most recent deposits within thecentral portion of the Trough are dominated by lacustrine, deltaic, and fluvial deposition associated withHolocene and Pleistocene stands of ancient Lake Cahuilla.Around the margins of the Salton Trough basin, relict shoreline features mark the former high stands ofancient Lake Cahuilla. The ancient lake repeatedly filled and occupied the basin during the Holocene. Themost recent, pre-Salton Sea filling is thought to have occurred about 1,650 years ago (Norris and others,1979). The lake may have been in existence as recently a several hundred years ago (Morton, 1977). Sandand gravel deposits along the ancient shoreline have been locally mined for aggregate. Travertine depositsdelineate ancient lake levels above the west side of the Sea.W:\27663042\00005-c-r.doc\1-Mar-04\SDG 3-1
Page 1: R E P O R TPreliminary In-Sea Geote
Page 4 and 5: TABLE OF CONTENTSSection 5 Prelimin
Page 6 and 7: List of Acronyms and AbbreviationsA
Page 8 and 9: Executive Summarysusceptible to sei
Page 10 and 11: SECTIONONEIntroductionvarious resto
Page 12 and 13: SECTIONTWOPreliminary Geotechnical
Page 16 and 17: SECTIONTHREESite ConditionsThe Salt
Page 18 and 19: SECTIONTHREESite Conditions3.4 SUBB
Page 20 and 21: SECTIONTHREESite ConditionsVery lit
Page 22 and 23: SECTIONFOURPotential Geologic And S
Page 24 and 25: SECTIONFIVEPreliminary Engineering
Page 32 and 33: SECTIONSIXPreliminary Embankment De
Page 34 and 35: SECTIONSIXPreliminary Embankment De
Page 36 and 37: SECTIONSEVENFurther StudiesSECTION
Page 38 and 39: SECTIONSEVENFurther Studiesparamete
Page 40 and 41: SECTIONNINEReferencesSECTION 9REFER
Page 42 and 43: SECTIONNINEReferencesRoberston, P.K
Page 44 and 45: TablesTable 1Summary of In-Sea Expl
Page 46 and 47: TablesTable 3Summary of Material Pr
Page 48 and 49: TablesTable 4 (continued)Summary of
Page 50 and 51: TablesTable 5Summary of Consolidate
Page 52 and 53: TablesTable 7Recent Large Earthquak
Page 54 and 55: TablesTable 9Results of Preliminary
Page 56 and 57: TablesTable 10Results of Prelimary
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APPENDIXAIn-Sea BoringsW:\27663042\
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APPENDIXAIn-Sea BoringsPortions of
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Project: Salton Sea RestorationProj
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APPENDIXCLaboratory TestingW:\27663
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APPENDIXCLaboratory TestingTable C-
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SAMPLE PHOTOGRAPHSSOFT LACUSTRINE D
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SAMPLE PHOTOGRAPHSUPPER STIFF LACUS
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SAMPLE PHOTOGRAPHSLOWER STIFF LACUS
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APPENDIXDStatic Slope Stability Ana
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Salton Sea Preliminary In-Sea Geotechnical Investigation

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