penetration test comparisons: modified california versus standard penetration test samplers...
TRANSCRIPT
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
• 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
Why?
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
efficiencyCN = overburden correction factor (to 1
atm,)CR = correction for “short” rod lengthCB = Correction for borehole diameterCS = 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 countN’ = measured blow countWH = 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
blowsUsing 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)
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
MLCLSM
MCS
SPT
<5 ft
MCS
MCS
SPT
SPT
<5 ft <5 ft
MCS-SPT MCS-MCS SPT-SPT
Consecutive samples taken in same lithologic layerin a particular boring, separated by 5 ft or less
San FranciscoBay Area DataSets
Los Angeles BasinData Sets
SPT vs SPT - SFBA
0 20 40 60 80NM1
0
20
40
60
80
NM
2
S P T B lo w s fo r S F B A d a ta ( 1 = d e e p e s t )
0 20 40 60 80N1601
0
20
40
60
80
N16
02
N 1 6 0 's f r o m S P T B lo w s fo r S F B A ( 1 = d e e p e s t )
Raw blows Converted to N1,60’s
Deeper sample
Sh
allow
er
sam
ple
SPT Blows
SPT B
low
s
N1,60
N1,6
0
N=1121
Residuals from 1:1 relation
-50 -30 -10 10 30 50RESIDBLOW_1
0
100
200
300
Cou
nt
0.0
0.1
0.2 Proportion per B
ar
-50 -30 -10 10 30 50RESIDN160_1
0
100
200
300
Cou
nt
0.0
0.1
0.2 Proportion per B
ar
Mean = -1.215 SD = 11.35
Mean = 0.424 SD = 12.32
Residuals in SPT Blows Shallower - Deeper
Residuals in N1,60’s
Raw blows Converted to N1,60’s
SPT-SPT
SPT vs SPT - LA Basin
0 20 40 60 80NM1
0
20
40
60
80
NM
2
S P T B lo w s - L A B ( 1 = d e e p e s t )
0 20 40 60 80N1601
0
20
40
60
80
N16
02
N 1 6 0 c a lc u la te d f r o m S P T B lo w s - L A B ( 1 = d e e p e s t )
Raw blows Converted to N1,60’s
Sh
allow
er
sam
ple
Deeper sample
SPT Blows
SPT B
low
s
N1,60
N1,6
0
N=805
MCS vs MCS - SFBA
0 20 40 60 80BLOW_COUNT1
0
20
40
60
80
BLO
W_C
OU
NT
2
M C S B lo w s fo r S F B A - ( 1 = d e e p e s t )
0 20 40 60 80N1601
0
20
40
60
80
N16
02
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 )
Raw blows Converted to N1,60’s
Sh
allow
er
sam
ple
Deeper sample
MCS Blows
MC
S B
low
s
N1,60
N1,6
0
N=1077
Residuals from 1:1 relation
Mean = -0.673 SD = 11.68
Mean = 0.826 SD = 9.83
-50 -30 -10 10 30 50RESIDBLOW_1
0
100
200
300
Cou
nt
0.0
0.1
0.2
Proportion per B
ar
-50 -30 -10 10 30 50RESIDN160_1
0
100
200
300
Cou
nt
0.0
0.1
0.2
Proportion per B
ar
Residuals in MCS Blows Shallower - Deeper
Residuals in N1,60’s
Raw blows Converted to N1,60’s
MCS-MCS
MCS vs MCS - LA Basin
0 10 20 30 40 50 60 70 80BLOW_COUNT1
0
10
20
30
40
50
60
70
80
BLO
W_C
OU
NT
2
M C S B L O W C O U N T S - L A B ( 1 = d e e p e r )
0 20 40 60 80N1601
0
20
40
60
80
N16
02
N 1 6 0 's c o m p u te d f r o m M C S B lo w s - L A B ( 1 = d e e p e r )
Raw blows Converted to N1,60’s
Sh
allow
er
sam
ple
Deeper sample
SPT BlowsMCS Blows
MC
S B
low
s
N1,60
N1,6
0
N=139
MCS vs SPT - SFBA
0 20 40 60 80BLOW_COUNT
0
20
40
60
80
NM
0 20 40 60 80N1602
0
20
40
60
80
N16
01
Raw blows Converted to N1,60’s
MCS sample
SP
T s
am
ple
MCS Blows
SPT B
low
s
N1,60
N1,6
0
N1,60 from MCS
N1,6
0 fr
om
SPT
N=129
Residuals from 1:1 relation
Mean = -7.46 SD = 14.69
Mean = -1.246 SD = 13.42
-50 -30 -10 10 30 50RESIDBLOWS_1
0
10
20
30
40
50
Cou
nt
0.0
0.1
0.2
0.3 Proportion per B
ar
-50 -30 -10 10 30 50RESIDN160
0
10
20
30
40
50
Cou
nt
0.0
0.1
0.2
0.3 Proportion per B
ar
Raw blows Converted to N1,60’s
Residuals between SPT & MCS Blows Residuals in N1,60’s
MCS-SPT
MCS vs SPT - LA Basin
0 20 40 60 80BLOW_COUNT
0
20
40
60
80
NM
M C S b lo w s v s S P T b lo w s fo r L A B
0 20 40 60 80N1602
0
20
40
60
80
N16
01
N 1 6 0 f r o m M C S v s N 1 6 0 f r o m S P T ( 1 ) - L A B
Raw blows Converted to N1,60’s
MCS Blows
SPT B
low
s
N1,60 from MCS
N1,6
0 fr
om
SPT
MCS sample
SP
T s
am
ple
N=104
Residuals from 1:1 relation
Mean = -8.73 SD = 12.51
Mean = -5.07 SD = 10.78
Raw blows Converted to N1,60’s
-50 -30 -10 10 30 50RESIDBLOWS
0
10
20
30
40
50
Cou
nt
0.0
0.1
0.2
0.3
0.4
Proportion per B
ar
-50 -30 -10 10 30 50RESIDN160
0
10
20
30
40
50
Cou
nt
0.0
0.1
0.2
0.3
0.4
Proportion per B
ar
Residuals in N1,60’sResiduals between SPT & MCS Blows
MCS-SPT
0
20
40
60
80
0 20 40 60 80
0
20
40
60
80
0 20 40 60 80
Adjusted N1,60’s from MCS Blows
N160’s
fro
m S
PT B
low
s
Y=0.45x + 9.16
MCS-SPT LS regression - SFBA
MCS-SPT LS regression - LA Basin
0
20
40
60
80
0 20 40 60 800
20
40
60
80
N160’s
fro
m S
PT B
low
s
0 20 40 60 80
Adjusted N1,60’s from MCS Blows
Y=0.33x + 6.10
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?
Lithologies for MCS-SPT data sets
CL
ML
SC
SM
SPSW
CL
CH
GC,GM,GPMLSC
SM
SP
SW
SFBA LA Basin
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