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
N1,60’s
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
Raw blows
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
N
N1602
1,60
40
40
20
20
0
0
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
60
NM2
Shallower sample
80
Converted to N1,60’s
20
40
SPT NM1
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 N1,60’s
Mean = 0.424
SD = 12.32
300
300
0
-50
-30
-10
10
RESIDBLOW_1
0.0
50
30
200
Count
Count
0.1
100
0.2
0.1
100
0
-50
Residuals in SPT Blows
Shallower - Deeper
SPT-SPT
-30
-10
10
RESIDN160_1
30
Residuals in N1,60’s
0.0
50
Proportion per Bar
200
Proportion per Bar
0.2
SPT vs SPT - LA Basin
Raw blows
S P T B lo w s - L A B ( 1 = d e e p e s t )
80
40
20
0
0
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
N1602
1,60
60
NM2
Shallower sample
80
Converted to N1,60’s
40
20
20
40
SPTNM1
Blows
60
Deeper sample
80
0
0
20
40
NN1601
60
80
1,60
N=805
MCS vs MCS - SFBA
Raw blows
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 )
M C S B lo w s f o r S F B A - ( 1 = d e e p e s t )
80
60
60
N
N1602
1,60
BLOW_COUNT2
Shallower sample
80
Converted to N1,60’s
40
20
0
0
40
20
20
40
60
BLOW_COUNT1
MCS
Blows
Deeper sample
80
0
0
20
40
NN1601
60
80
1,60
N=1077
Residuals from 1:1 relation
Raw blows
Mean = -0.673
SD = 11.68
Converted to N1,60’s
Mean = 0.826
SD = 9.83
300
300
-30
-10
10
RESIDBLOW_1
30
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 N1,60’s
0.0
50
Proportion per Bar
0.1
100
Proportion per Bar
0.2
200
MCS vs MCS - LA Basin
Raw blows
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
M C S B L O W C O U N T S - L A B (1 = d e e p e r)
80
70
60
60
50
N
N1602
1,60
BLOW_COUNT2
Shallower sample
80
Converted to N1,60’s
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 N1,60’s
80
80
60
60
N1,60 from
N
N1601
1,60 SPT
NM
SPT sample
Raw blows
40
20
0
0
20
40
60
BLOW_COUNT
MCS Blows
MCS sample
80
40
20
0
0
20
N1,60
40
60
N1602
N
from
MCS
80
1,60
N=129
Residuals from 1:1 relation
Raw blows
Mean = -7.46
SD = 14.69
Converted to N1,60’s
Mean = -1.246
SD = 13.42
50
50
0.2
20
0.1
10
0
-50
Count
30
40
0.3
30
0.2
20
0.1
10
-30
-10
10
RESIDBLOWS_1
30
0.0
50
0
-50
Residuals between SPT & MCS Blows
MCS-SPT
-30
-10
10
RESIDN160
30
Residuals in N1,60’s
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
SPT
N1,60 from
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 sample
80
Converted to N1,60’s
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
Mean = -5.07
SD = 10.78
50
50
0.4
20
0.2
10
0.1
0
-50
-30
-10
10
RESIDBLOWS
30
0.0
50
Count
0.3
30
0.3
20
0.2
10
0.1
0
-50
Residuals between SPT & MCS Blows
MCS-SPT
-30
-10
10
RESIDN160
30
Residuals in N1,60’s
0.0
50
Proportion per Bar
30
0.4
40
Proportion per Bar
Count
40
MCS-SPT LS regression - SFBA
80
80
60
60
40
40
Y=0.45x + 9.16
20
20
0
0
0
0
20
20
40
40
60
60
80
80
Adjusted N1,60’s from MCS Blows
MCS-SPT LS regression - LA Basin
80
80
60
60
40
40
Y=0.33x + 6.10
20
20
0
0
0
0
20
20
40
40
60
60
80
80
Adjusted N1,60’s 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
ML
GC,GM,GP
SM
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