1 / 25

PENETRATION TEST COMPARISONS: MODIFIED CALIFORNIA VERSUS STANDARD PENETRATION TEST SAMPLERS

PENETRATION TEST COMPARISONS: MODIFIED CALIFORNIA VERSUS STANDARD PENETRATION TEST SAMPLERS. Jacqueline D.J. Bott, Keith L. Knudsen & Charles R. Real California Geological Survey. Outline of talk. Why comparison is important Review of N 1,60 calculation

jennis
Download Presentation

PENETRATION TEST COMPARISONS: MODIFIED CALIFORNIA VERSUS STANDARD PENETRATION TEST SAMPLERS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

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 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)(2.02-1.3752)/(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. 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)

  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 SPT MCS

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

  12. Residuals from 1:1 relation Raw blows Converted to N1,60’s Mean = -1.215 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 Shallowersample N1,60 SPT Blows SPT Blows N1,60 Deeper sample N=805

  14. MCS vs MCS - SFBA Raw blows Converted to N1,60’s Shallowersample N1,60 MCS Blows MCS Blows N1,60 Deeper sample N=1077

  15. Residuals from 1:1 relation Raw blows Converted to N1,60’s Mean = -0.673 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 Shallowersample N1,60 MCS Blows MCS Blows SPT Blows N1,60 Deeper sample N=139

  17. MCS vs SPT - SFBA Raw blows Converted to N1,60’s N1,60 N1,60 from SPT SPTsample 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 = -1.246 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 N1,60 from SPT SPTsample 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 - SFBA 80 60 40 N160’s from SPT Blows Y=0.45x + 9.16 20 0 0 20 40 60 80 Adjusted N1,60’s from MCS Blows

  22. MCS-SPT LS regression - LA Basin 80 60 40 N160’s from SPT Blows Y=0.33x + 6.10 20 0 0 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 LABasin 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

More Related