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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 N1,60 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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Why? CGS calculates N1,60 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 N1,60

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**Review of N1,60 calculation**

N1,60 = Nm.CE.CN.CR.CB. CS Where Nm = measured blows (using SPT sampler) CE = Correction for hammer energy efficiency CN = overburden correction factor (to 1 atm,) CR = correction for “short” rod length CB = Correction for borehole diameter CS = Correction for non-standard sampler

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**Conversion to SPT-equivalent from non-standard samplers**

N=N’(WH/4200)( )/(OD2-ID2) (Burmister, 1948) N=N’(WH/4200)(2/OD2) (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. Burmister (1948) LaCroix & Horn (1973) Other definition of MCS: ID = 2.5 in (2.4 with liners) & OD = 3.0 in Burmister (1948) 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 CN (and rod length for shallow samples) will be different so also compare N1,60’s

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**Consecutive samples taken in same lithologic layer **

in a particular boring, separated by 5 ft or less MCS-SPT MCS-MCS SPT-SPT SM CL ML MCS MCS SPT <5 ft <5 ft <5 ft SPT MCS SPT

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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 blows Converted to N1,60’s Shallower sample**

SPT Blows SPT Blows N1,60 Deeper sample N=1121

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**Residuals from 1:1 relation**

Raw blows Converted to N1,60’s Mean = SD = 11.35 Mean = 0.424 SD = 12.32 Residuals in SPT Blows Shallower - Deeper Residuals in N1,60’s SPT-SPT

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**SPT vs SPT - LA Basin Raw blows Converted to N1,60’s Shallower sample**

SPT Blows SPT Blows N1,60 Deeper sample N=805

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**MCS vs MCS - SFBA Raw blows Converted to N1,60’s Shallower sample**

MCS Blows N1,60 MCS Blows N1,60 Deeper sample N=1077

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**Residuals from 1:1 relation**

Raw blows Converted to N1,60’s Mean = SD = 11.68 Mean = 0.826 SD = 9.83 Residuals in MCS Blows Shallower - Deeper Residuals in N1,60’s MCS-MCS

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**MCS vs MCS - LA Basin Raw blows Converted to N1,60’s Shallower sample**

MCS Blows N1,60 MCS Blows SPT Blows N1,60 Deeper sample N=139

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**MCS vs SPT - SFBA Raw blows Converted to N1,60’s SPT sample MCS sample**

N1,60 from SPT N1,60 SPT sample SPT Blows MCS Blows N1,60 from MCS N1,60 MCS sample N=129

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**Residuals from 1:1 relation**

Raw blows Converted to N1,60’s Mean = -7.46 SD = 14.69 Mean = SD = 13.42 Residuals between SPT & MCS Blows Residuals in N1,60’s MCS-SPT

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**MCS vs SPT - LA Basin Raw blows Converted to N1,60’s SPT sample**

N1,60 from SPT SPT sample SPT Blows N1,60 from MCS MCS Blows MCS sample N=104

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**Residuals from 1:1 relation**

Raw blows Converted to N1,60’s Mean = -8.73 SD = 12.51 Mean = -5.07 SD = 10.78 Residuals between SPT & MCS Blows Residuals in N1,60’s MCS-SPT

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**MCS-SPT LS regression - SFBA**

80 60 40 N160’s from SPT Blows Y=0.45x 20 20 40 60 80 Adjusted N1,60’s from MCS Blows

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**MCS-SPT LS regression - LA Basin**

80 60 40 N160’s from SPT Blows Y=0.33x 20 20 40 60 80 Adjusted N1,60’s from MCS Blows

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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 (N1,60) 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**

SFBA LA Basin SW SW CH SP CL SP CL ML SM SC SM SC ML GC,GM,GP

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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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