Salton Sea Preliminary In-Sea Geotechnical Investigation

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SECTIONFIVEPreliminary Engineering CharacterizationThe time over which settlement could occur is calculated using c v , which is a function of soil permeabilityand therefore the choice of this parameter can vary considerably. For this study, the parameter wasinterpreted from oedometer tests and published correlations to liquid limit.5.2 SEAFLOOR DEPOSITS5.2.1 Index PropertiesThis unit consists predominantly of fine-grained materials. Most of the soils were classified as fat clay(Unified Soil Classification of CH). However, the average fines content (silt and clay) variedconsiderably (14 to 100 percent) and averaged about 64 percent, with the remaining fraction comprisingfine sand. The plasticity of this unit is high based on an average Plasticity Index (PI) of 48%. The averagewater content (63%) is nearer to the average Liquid Limit (LL) of 77% relative to the average PlasticLimit (PL, 30%). Table 3 summarizes the index test data.The consistency of fine-grained materials ranged from firm to stiff at shallow water locations andpredominately soft and locally firm at deep-water locations (mid-Sea locations only). Where coarsegrainedmaterials exist, the relative density ranged from loose to medium dense.The SBT interpretations show similar variability between coarse- and fine-grained materials. SBT mostlyranged from clay to sand and silt mixtures as shown on the CPT plots in Appendix B (mid-Sea locationsonly). More variability was evident at shallow water locations.5.2.2 StrengthThe c u of this unit ranges from about 75 to 200 pounds per square foot (psf) considering six UU triaxialcompression test results and discounting one anomalous test of 800 psf. The undrained shear strengthdeveloped from four ICU triaxial compression test points (Mohr Circles) tested at a confining pressureapproximately equal to effective overburden pressure ranged from 300 to 660 psf. The ICU dataproduced higher undrained shear strengths, when comparing the two data sets (UU and ICU).Data from Torvane TM tests were only considered qualitatively, which shows a marked increase inundrained shear strength at shallow water locations.Undrained shear strength for normally consolidated soils is often presented as the ratio of undrained shearstrength to effective overburden stress (σ v ’) for slope stability and other forms of geotechnical analyses.A c u /σ v ’ ratio of 0.35 was interpreted from the data for conceptual design. This assessment considers adesign line interpreted from a scatter plot of undrained shear strength versus effective stress (refer toFigure 22) and published correlations to index parameters (also shown on Figure 22).Data from the ICU triaxial compression tests and reference to published correlations to index tests wereused to estimate peak and ultimate effective cohesion (c') and friction angle (φ'). A cohesion of zero psfand friction angle of 27 and 25 degrees for peak and ultimate conditions respectively were interpretedfrom the data. The ultimate condition is defined as the point where continuous shear defomation continueswith no further changes in volume. To interpret these parameters, Mohr circle plots of shear stress versusW:\27663042\00005-c-r.doc\1-Mar-04\SDG 5-4
SECTIONFIVEPreliminary Engineering Characterizationeffective stress were developed at individual sample locations and for all the samples within the unit,excluding anomalous points. Figures in Appendix C of this report provide the test results.5.2.3 CompressibilityThis unit is interpreted to be slightly overconsolidated with an OCR of 1.5 recommended for conceptualdesign. A graphical interpretation of the preconsolidation pressure (σ p ) using the strain versus the log ofvertical effective stress (σ v ’) test data was the primary method of interpretation. However, engineeringjudgment considering the varied geologic environment of the surface of the Sea bottom along withundrained shear strength versus depth profiles were also considered to develop this assessment.Assessment of OCR based on the water content relative to the Liquid and Plastic Limit, could suggest adifferent interpretation for this unit and the other fine-grained soil units. However, for conceptual designpurposes, we recommend adopting normally consolidated to slightly overconsolidated conditions.A C C of 0.65 and C r of 0.10 are recommended for conceptual design. The C c data from six tests rangedfrom 0.23 to 1.10. One sample swelled and therefore it was discounted from further interpretation. Theseparameters were developed from graphical interpretations of the strain versus log of effective stress (σ v ’)plots and inspection of this data relative to a plot of CR correlated to water content (refer to Figure 23).The Compression Index was also related to the commonly used expression C C = 0.009 (LL-10). Therecommended C r was taken as 15 percent of the C C . Table 6 summarizes the consolidation test data.A complete discussion of potential consolidation settlement is presented elsewhere in this report.However, an average LI of 0.81 suggests a potential for significant consolidation settlement.A coefficient of consolidation (c v ) of 15 feet squared per year (ft 2 /yr) is recommended for conceptualdesign. However, considering the variability of this parameter, conceptual design analyses shouldconsider using a range from 10 to 40 ft 2 /yr. This parameter was developed using the relevant portions ofthe oedometer test data and correlation to the LL. The lab data ranged from 8 to 43 ft 2 /yr. Correlations toLiquid Limit ranged from 12 to 40 ft 2 /yr.5.3 SOFT LACUSTRINE DEPOSITS5.3.1 Index PropertiesSamples tested from this unit consist of fine-grained materials classified predominantly as fat clay (CH).The plasticity of these materials is high based on the average PI of 40%. The average water content (43%)is nearer to the average PL (26%) relative to an average LL of 66%. Table 3 summarizes the index testdata. The consistency was generally stiff for shallow water locations and soft to firm for deep-waterlocations (mid-Sea locations only).The SBT ranged from sand and silt mixtures to clay and silt mixtures. Shallow water location appeared toexhibit a tendency towards more coarse-grained SBT interpretations as shown on the CPT plots inAppendix B (mid-Sea locations only).W:\27663042\00005-c-r.doc\1-Mar-04\SDG 5-5
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 14 and 15: 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
Page 58: FiguresW:\27663042\00005-c-r.doc\1-
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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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APPENDIXBIn-Sea Cone Penetration Te
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APPENDIXCLaboratory TestingW:\27663
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APPENDIXCLaboratory TestingTable C-
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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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