Penetration Test Comparisons: Modified California Versus ...
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 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 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 SPTequivalent blow count in order to calculate N1,60 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 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) 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 0.64 Burmister (1948) LaCroix & Horn (1973) Other definition of MCS: ID = 2.5 in (2.4 with liners) & OD = 3.0 in 0.65 0.44 Burmister (1948) LaCroix & Horn (1973)
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 N1,60s Consecutive samples taken in same lithologic layer in a particular boring, separated by 5 ft or less MCS-SPT MCS-MCS MCS <5 ft SM MCS <5 ft CL SPT SPT-SPT SPT <5 ft ML MCS SPT San Francisco Bay Area Data Sets Los Angeles Basin
Data Sets SPT vs SPT - SFBA Converted to N1,60s S P T B lo w s f o r S F B A d a t a ( 1 = d e e p e s t ) 80 80 N 1 6 0 's f r o m S P T B lo w s f o r S F B A ( 1 = d e e p e s t ) 60 N N1602 1,60 60 Blows SPT NM2 Shallower sample Raw blows 40 40 20 20 0 0
20 40 NM1 SPT Blows 60 Deeper sample 80 0 0 20 40 NN1601 60 80 1,60 N=1121 Residuals from 1:1 relation Raw blows Mean = -1.215 SD = 11.35 Converted to N 1,60s = 0.424 Mean SD = 12.32
SPT-SPT -30 -10 10 RESIDN160_1 30 Residuals in N1,60s 0.0 50 Proportion per Bar 200 Proportion per Bar 0.2 SPT vs SPT - LA Basin Converted to N1,60s S P T B lo w s - L A B ( 1 = d e e p e s t ) 80 80 N 1 6 0 c a lc u la t e d f r o m S P T B lo w s - L A B ( 1 = d e e 60 N
40 NN1601 60 80 1,60 N=805 MCS vs MCS - SFBA Converted to N1,60s M C S B lo w s f o r S F B A - ( 1 = d e e p e s t ) 80 80 60 N 1 6 0 's f r o m M C S B lo w s - S F B A ( 1 = d e e p e s t ) 60 N N1602 1,60 BLOW_COUNT2 MCS Blows Shallower sample Raw blows 40
Mean = -0.673 SD = 11.68 Converted to N 1,60s = 0.826 Mean SD = 9.83 300 300 -30 -10 10 30 RESIDBLOW_1 0.0 50 Count Count 0 -50 0.2 200 0.1 100 0 -50
Residuals in MCS Blows Shallower - Deeper MCS-MCS -30 -10 10 RESIDN160_1 30 Residuals in N1,60s 0.0 50 Proportion per Bar 0.1 100 Proportion per Bar 0.2 200 MCS vs MCS - LA Basin Converted to N1,60s M C S B L O W C O U N T S - L A B (1 = d e e p e r) 80
80 N 1 6 0 's c o m p u t e d f r o m M C S B lo w s - L A B ( 1 = d e 70 60 60 50 N N1602 1,60 BLOW_COUNT2 MCS Blows Shallower sample Raw blows 40 40 30 20 20 10 0 0 10 20 30 40 50 60 70 80 BLOW_COUNT1 MCS SPT Blows
Deeper sample 0 0 20 40 NN1601 60 80 1,60 N=139 MCS vs SPT - SFBA Converted to N1,60s 80 80 60 60 N1,60 from N N1601 1,60 SPT NM SPT Blows
1,60 N=129 Residuals from 1:1 relation Raw blows Mean = -7.46 SD = 14.69 Converted to NMean 1,60s = -1.246 SD = 13.42 50 50 0.2 20 0.1 10 0 -50 -30 -10 10 30 RESIDBLOWS_1 0.0 50 Count
30 40 0.3 30 0.2 20 0.1 10 0 -50 Residuals between SPT & MCS Blows MCS-SPT -30 -10 10 RESIDN160 30 Residuals in N1,60s 0.0 50 Proportion per Bar 0.3 Proportion per Bar Count
40 MCS vs SPT - LA Basin Raw blows M C S b lo w s v s S P T b lo w s f o r L A B 80 N1601 N1,60 from SPT 40 20 0 0 N 1 6 0 fro m M C S v s N 1 6 0 fro m S P T (1 ) - L A B 60 60 NM SPT Blows SPT sample 80 Converted to N1,60s 20 40
60 BLOW_COUNT MCS Blows MCS sample 80 40 20 0 0 20 N1,60 40 60 N1602MCS from 80 N=104 Residuals from 1:1 relation Raw blows Mean = -8.73 SD = 12.51 Converted to N1,60 s = -5.07 Mean SD = 10.78
Adjusted N1,60s from MCS Blows MCS-SPT LS regression - LA Basin N160s from SPT Blows 8 0 80 6 0 60 4 0 40 Y=0.33x + 6.10 2 0 20 00 0 0 2 0 20 4 0 40
6 0 60 8 0 80 Adjusted N1,60s from MCS Blows Conclusions so far... There is a large scatter in blow count data - both for SPT and MCS CGS conversion from MCS to SPTequivalent (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? Lithologies for MCS-SPT data sets SFBA SW LA Basin CH SP SP SW CL CL ML
SM SC SC SM ML GC,GM,GP 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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