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PENETRATION TEST COMPARISONS: MODIFIED CALIFORNIA VERSUS STANDARD PENETRATION TEST SAMPLERS Jacqueline D.J. Bott, Keith L. Knudsen & Charles R. Real California Geological Survey

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Outline of talk Why comparison is important Review of N 1,60 calculation Conversion used to correct MCS blows to SPT-equivalent blow count How did we do the comparison Location of data Results Conclusions so far and future work

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CGS calculates N 1,60 from SPT N-values for liquefaction analyses to help define Seismic Hazard Zones of Required Investigation. CGS utilizes geotechnical boring data collected from cities & counties etc. Consultants often use MCS instead of SPT (ASTM 1526, 6066) for determining penetration resistance Need to convert MCS blows to SPT- equivalent blow count in order to calculate N 1,60 Why?

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Review of N 1,60 calculation N 1,60 = Nm.C E.C N.C R.C B. C S Where Nm = measured blows (using SPT sampler) C E = Correction for hammer energy efficiency C N = overburden correction factor (to 1 atm,) C R = correction for “short” rod length C B = Correction for borehole diameter C S = Correction for non-standard sampler

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Conversion to SPT-equivalent from non-standard samplers N=N’(WH/4200)(2.0 2 -1.375 2 )/(OD 2 -ID 2 ) (Burmister, 1948) N=N’(WH/4200)(2/OD 2 ) (LaCroix & Horn, 1973) where N = SPT-equivalent blow count N’ = measured blow count WH = hammer mass (lbs) x fall distance (in) OD = outer diameter of non-standard sampler (in) ID = inner diameter of non-standard sampler (in)

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Conversion factors for MCS to SPT-equivalent blows Using CGS Definition of MCS: ID = 2.0 in (1.875 in with liners) & OD = 2.5 in. 0.77 Burmister (1948) 0.64 LaCroix & Horn (1973) Other definition of MCS: ID = 2.5 in (2.4 with liners) & OD = 3.0 in 0.65 Burmister (1948) 0.44 LaCroix & Horn (1973)

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How? Compare consecutive samples (MCS & SPT) from same lithologic layer in a particular boring, that are within 5 ft of each other. Direct comparison of two such values cancels out factors often not reported by consultants such as hammer energy, borehole diameter etc. Only C N (and rod length for shallow samples) will be different so also compare N 1,60 ’s

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MLCL SM MCS SPT <5 ft MCS SPT <5 ft MCS-SPTMCS-MCSSPT-SPT Consecutive samples taken in same lithologic layer in a particular boring, separated by 5 ft or less

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San Francisco Bay Area Data Sets

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Los Angeles Basin Data Sets

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SPT vs SPT - SFBA Raw blowsConverted to N 1,60 ’s Deeper sample Shallower sample SPT Blows N 1,60 N=1121

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Residuals from 1:1 relation Mean = -1.215 SD = 11.35 Mean = 0.424 SD = 12.32 Residuals in SPT Blows Shallower - Deeper Residuals in N 1,60 ’s Raw blowsConverted to N 1,60 ’s SPT-SPT

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SPT vs SPT - LA Basin Raw blowsConverted to N 1,60 ’s Shallower sample Deeper sample SPT Blows N 1,60 N=805

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MCS vs MCS - SFBA Raw blowsConverted to N 1,60 ’s Shallower sample Deeper sample MCS Blows N 1,60 N=1077

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Residuals from 1:1 relation Mean = -0.673 SD = 11.68 Mean = 0.826 SD = 9.83 Residuals in MCS Blows Shallower - Deeper Residuals in N 1,60 ’s Raw blowsConverted to N 1,60 ’s MCS-MCS

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MCS vs MCS - LA Basin Raw blowsConverted to N 1,60 ’s Shallower sample Deeper sample SPT BlowsMCS Blows N 1,60 N=139

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MCS vs SPT - SFBA Raw blowsConverted to N 1,60 ’s MCS sample SPT sample MCS Blows SPT Blows N 1,60 N 1,60 from MCS N 1,60 from SPT N=129

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Residuals from 1:1 relation Mean = -7.46 SD = 14.69 Mean = -1.246 SD = 13.42 Raw blowsConverted to N 1,60 ’s Residuals between SPT & MCS BlowsResiduals in N 1,60 ’s MCS-SPT

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MCS vs SPT - LA Basin Raw blowsConverted to N 1,60 ’s MCS Blows SPT Blows N 1,60 from MCS N 1,60 from SPT MCS sample SPT sample N=104

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Residuals from 1:1 relation Mean = -8.73 SD = 12.51 Mean = -5.07 SD = 10.78 Raw blowsConverted to N 1,60 ’s Residuals in N 1,60 ’sResiduals between SPT & MCS Blows MCS-SPT

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0 20 40 60 80 020406080 Adjusted N 1,60 ’s from MCS Blows N160’s from SPT Blows Y=0.45x + 9.16 MCS-SPT LS regression - SFBA

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MCS-SPT LS regression - LA Basin 0 20 40 60 80 N160’s from SPT Blows 020406080 Adjusted N 1,60 ’s from MCS Blows Y=0.33x + 6.10

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Conclusions so far... There is a large scatter in blow count data - both for SPT and MCS CGS conversion from MCS to SPT- equivalent (N 1,60 ) gives more consistent results for SFBA than for LA Basin. Is MCS defined differently in the two locations? Is this a function of the geology? Or related to something else?

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Lithologies for MCS-SPT data sets CL ML SC SM SP SW CL CH GC,GM,GPML SC SM SP SW SFBALA Basin

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Future work Effect of lithology, saturation, depth, presence of gravel, etc Investigate why residuals are not normally distributed Survey Consultants as to how they define MCS

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