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