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 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

3. 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

4. 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

5. 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)

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

8. 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

9. San Francisco
Bay Area Data
Sets

10. Los Angeles Basin
Data Sets

11. SPT vs SPT - SFBA Raw blows Converted to N1,60’s Shallower sample
SPT Blows
SPT Blows
N1,60
Deeper sample
N=1121

12. 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

13. SPT vs SPT - LA Basin Raw blows Converted to N1,60’s Shallower sample
SPT Blows
SPT Blows
N1,60
Deeper sample
N=805

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. MCS-SPT LS regression - SFBA80 60 40
N160’s from SPT Blows
Y=0.45x 20 20 40 60 80
Adjusted N1,60’s from MCS Blows

22. MCS-SPT LS regression - LA Basin80 60 40
N160’s from SPT Blows
Y=0.33x 20 20 40 60 80
Adjusted N1,60’s from MCS Blows

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 (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?

24. 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

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