Salton Sea Preliminary In-Sea Geotechnical Investigation

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SECTIONFIVEPreliminary Engineering CharacterizationIn-situ properties of the deposits include relative density (loose to very dense) for coarse-grainedmaterials and consistency (very soft to hard) for fine-grained materials. Field tests, such as SPT, CPT, orTorvane TM tests, and manual penetration (“thumbnail test”) of samples, were the main methods ofinterpretation of density or consistency.Physical properties were also interpreted using the SBT classification developed by Robertson (1990) foruse with CPT data. This study considered the relationship between cone tip resistance and friction ratio.5.1.2 StrengthsThe strength testing was concentrated in the soft seafloor and lacustrine deposits; the strength of thesedeposits will be a controlling factor in the stability of embankments constructed within the Sea. Innormally to lightly overconsolidated cohesive soils, such as the seafloor and soft lacustrine deposits, theundrained shear strength (c u ) is used to evaluate the short-term stability of embankments. The undrainedstrength is used to simulate that the soils may be loaded rapidly enough (with an embankment) that theinduced pore pressures do not dissipate enough for significant strength gain in the foundation soils. Fornormally consolidated soils, the c u is often directly proportional to the effective overburden pressure (σ v ’),the ratio c u /σ v ’ is typically 0.2 to 0.4 for normally or lightly overconsolidated clays.The c u has been assessed for this investigation using the following techniques:• Torvane TM tests on thin walled samples.• Unconsolidated Undrained (UU) triaxial compression test results.• Isotropically Consolidated Undrained (ICU) triaxial compression test results.A plot of the Torvane TM shear strength test data versus depth is shown in Figure 21. These results aregenerally much higher than what was indicated by the sample’s consistency, and the results of the UU andICU tests. A summary of the UU test results is presented in Table 4. A plot of c u versus the σ v ’ at the UUsample depth (or the confining pressure for ICU results) is presented in Figure 22 for the soft deposits.Effective stress shear strength parameters, c' (cohesion) and φ' (friction angle), are used to evaluate longterm stability conditions. ICU (with pore pressure measurements) triaxial compression tests wereperformed on the cohesive soils to evaluate these parameters. A summary of these test results is providedin Table 5. Preliminary values for the effective stress shear strength parameters for use in conceptualdesigns were interpreted from these results, and published correlations with other material properties.5.1.3 CompressibilityThe compressibility of the subbottom deposits will be a factor in maintaining sufficient freeboard on in-Sea embankments, and in estimating ultimate quantities of materials for embankment construction. Theconsolidation testing was also concentrated in the soft seafloor and lacustrine deposits as the largestmagnitudes of settlement will likely come from these deposits. A summary of the compressibilityparameters obtained from the consolidation testing is provided in Table 6.W:\27663042\00005-c-r.doc\1-Mar-04\SDG 5-2
SECTIONFIVEPreliminary Engineering CharacterizationThe compressibility characteristics of fine-grained materials have been interpreted from laboratoryoedometer testing and published correlations to index properties. Correlations to index properties wereused to interpret potential variability, considering the limited number of oedometer tests performed withineach deposit compared to the more numerous index testing. For example, the Liquidity Index (LI)provides qualitative assessments of the compressibility of fine-grained soils.LI is defined as:LI = (w-PL)/PIWhere: w = water contentPL = plastic limitPI = plasticity indexA LI less than or equal to zero may indicate a heavily overconsolidated soil. A LI equal to 1.0 may indicaterelatively weak and compressible materials. A LI greater than 1.0 may indicate that the material is sensitive.Soils with a LI greater than approximately 0.7 may experience significant consolidation settlements.The parameters used to characterize compressibility are the Compression Index (C c ), RecompressionIndex (C r ), Overconsolidation Ratio (OCR or σ p ’ /σ v ’ ) and/or Preconsolidation Pressure (σ p ’), Coefficientof Secondary Compression (C α ) and the Coefficient Consolidation (c v ).The C c was interpreted as the slope of the oedometer test data in the range of the anticipated stresschanges, as shown below:C c = ∆e / ∆ log σ v 'Where: ∆e = change in void ratio∆σ v ’ = change in effective vertical overburden stressThe C r has been interpreted from the reloading portion of the laboratory oedometer testing, or taken to bethe commonly adopted values of ten to twenty percent of C c .The Overconsolidation Ratio (OCR) and Preconsolidation Pressure (σ p ’) were estimated by inspection ofthe strain – log σ’ oedometer test data and various published correlations to index parameters.The Compression Ratio (CR) is related to C c as follows:CR = C c / (1 + e 0 )Where: e 0 = initial void ratioThe CR is also commonly related to natural water content; a plot of published correlations with test datafrom this investigation is shown in Figure 23.Conceptual design parameters for secondary compression have not been developed for this study. Themagnitude of secondary compression should provide a relatively small contribution to overall settlement,or be part of a long-term maintenance burden, depending on the design life adopted.W:\27663042\00005-c-r.doc\1-Mar-04\SDG 5-3
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 26 and 27: 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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Page 62 and 63: Standard penetration samplePunch Co
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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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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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