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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.

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Presentation on theme: "PENETRATION TEST COMPARISONS: MODIFIED CALIFORNIA VERSUS STANDARD PENETRATION TEST SAMPLERS Jacqueline D.J. Bott, Keith L. Knudsen & Charles R. Real California."— Presentation transcript:

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

2 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

3 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?

4 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

5 Conversion to SPT-equivalent from non-standard samplers N=N’(WH/4200)( )/(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)

6 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) 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)

7 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

8 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

9 San Francisco Bay Area Data Sets

10 Los Angeles Basin Data Sets

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

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

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

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

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

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

17 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

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

19 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

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

21 Adjusted N 1,60 ’s from MCS Blows N160’s from SPT Blows Y=0.45x MCS-SPT LS regression - SFBA

22 MCS-SPT LS regression - LA Basin N160’s from SPT Blows Adjusted N 1,60 ’s from MCS Blows Y=0.33x

23 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?

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

25 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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