Geotechnical Site Characterization by Cone

Penetration Testing

Mid-America

Earthquake Center

Paul W. Mayne, PhD, P.E.

Professor, Geosystems

Civil & Environmental Engineering

FHWA

Standard Penetration Test63.5-kg DropHammerRepeatedlyFalling 0.76 mAnvil

Split-Barrel(Drive) Sampler: O.D. = 50 mm I.D. = 35 mm L = 760 mm

Rotary-drilledBorehole

Standard Penetration Test (SPT)Procedures: ASTM D 1586N = measured Number of Blows to drive sampler 300 mm into soil.

Representative SPT Profile

Downtown Memphis

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SPT-N (bpf)D

ep

th (

me

ters

)

1982 B1

1982-B3

1982-B5

Soil Profile

Silty Sand

Sandy Silt

Gravelly Sand

Desiccated OC Clay

Clayey Sand

OC Clay

Fill

Gravelly Sand

Corrections to SPT N-value 

Effect 

Variable 

Term 

Value 

Overburden Stress

vo' CN (Pa/vo')0.5 but <

2Energy Ratio1

·        Safety Hammer·        Donut Hammer·        Automatic Hammer

CE0.6 to 0.850.3 to 0.6

0.85 to 1.0

Borehole Diameter

·        65 to 115 mm·        150 mm·        200 mm

CB 1.001.051.15

Sampling Method

·        Standard sampler·        Sampler without liner

CS 1.01.1 to 1.3

Rod Length

·        10 m to 30 m·        6 to 10 m·        4 to 6 m·        3 to 4 m

CR1.0

0.950.850.75

Particle Size

Median Grain Size (D50) of Sand in mm

CP 60 + 25 log D50

Aging 

Time (t) in years since deposition

CA 1.2 + 0.05 log (t/100)

Overconsolidation 

OCR COCR OCR0.2

1 Obtain by energy measurement per ASTM D4633

Corrections to SPT N-value

Nmeasured = Raw SPT Resistance (ASTM D 1586).

N60 = (ER/60) Nmeasured = Energy-Corrected N Value

where ER = energy ratio (ASTM D 4633). Note: 30% < ER < 100% with average ER = 60% in the U.S.

N60 CE CB CS CR Nmeas = Estimated corrected N

(N1)60 = CN N60 = Energy-Corrected SPT Value

normalized to an effective overburden stress of one

atmosphere: (N1)60 = (N60)/(vo’)0.5 with stress given

in atm. (Note: 1 atm = 1 bar = 100 kPa = 1 tsf).

Cone Penetrometers

Electronic Steel Probes with 60° Apex Tip ASTM D 5778 Procedures Hydraulic Push at 20 mm/s No Boring, No Samples, No Cuttings, No Spoil Continuous readings of stress, friction, pressure

Cone Penetration Tests (CPT)

Mobile 25-tonne rigs withenclosed cabins to allowtesting under all weather conditions

Cone Trucks

Corrections to CPT

• Tip Stress correction for porewater pressures on unequal areas – Important in Intact Clays & Silts

• Sleeve Friction correction for porewater pressures – Use equal end areas on friction sleeve

• Baseline corrections – Obtain before & after sounding

Anchored Cone Rig

6-tonne Geostar truck with 20-tonne hydraulic pushing system

No special license

Twin earth anchors

Has penetrated to depths over 32+ meters at sites in SC, AL, MO, TN, & AL

Mud Island, Downtown Memphis, TN

CPT Profile, Downhole Memphis

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28

0 20 40 60

qt (MPa)

De

pth

(m

ete

rs)

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0 500 1000

fs (kPa) u b (kPa)

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-200 0 200 400 600 800

qt

ub

fs

Comparison CPT and SPTDowntown Memphis

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SPT-N (bpf) and qc (MPa)

De

pth

(m

ete

rs)

1982 B1

1982-B3

1982-B5

CPT-qc (MPa)

60o

fs

qc

Vs

u1

u2

Cone Tip Stress, qt

Penetration Porewater Pressure, u Sleeve Friction, fs

Arrival Time of Downhole Shear Wave, ts

Cone Tip Stress, qt

Penetration Porewater Pressure, u Sleeve Friction, fs

Arrival Time of Downhole Shear Wave, ts

Obtains Four Independent Measurements with Depth:

Seismic Piezocone Test

Downhole Shear Wave Velocity

Anchoring System Automated Source Polarized Wave Downhole Vs

Anchoring System Automated Source Polarized Wave Downhole Vs

• Electronically-actuated

• Self-contained

• Left and right polarization

• Modified beam uses fin to enhance shear wave generation

• Successfully tested to depths of 20m

• Capable of being used with traditional impulse hammer

Automated Seismic Source

-0.08

-0.06

-0.04

-0.02

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0.02

0.04

0.06

0.08

0 50 100 150 200

Time (ms)

Am

plit

ud

e

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0 50 100 150 200

Time (ms)

Am

plit

ud

e

-400

-300

-200

-100

0

100

200

300

400

500

-200 -150 -100 -50 0 50 100 150 200

-400

-300

-200

-100

0

100

200

300

400

500

-5 0 5 10 15 20

Time shift (ms)

Maximum crosscorrelation at t = 6.75 ms

Shear wave velocity = 155 m/s

Right Strike

CROSSOVER Method

Left Strike

Shear Wave at 8.15 m

Shear Wave at 9.20 m

CROSSCORRELATION

Downhole Shear Waves

Sod Farm, Charleston, SCSeismic Cone Penetrometer Data School of Civil and Environmental EngineeringSounding performed for research Georgia Institute of Technology

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qt (MPa)

Dep

th (

m)

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32

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fs (kPa)

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-100 400 900 1400

U2, U0 (kPa)

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0 400 800

Vs (m/s)

CPT Soil Behavioral Classification

Soil Behavior Type (Robertson et al., 1986; Robertson & Campanella, 1988)1 – Sensitive fine grained 5 – Clayey silt to silty clay 9 – sand2 – Organic material 6 – Sandy silt to silty sand 10 – Gravelly sand to sand3 – Clay 7 – Silty sand to sandy silt 11 – Very stiff fine grained*4 – Silty clay to clay 8 – Sand to silty sand 12 – Sand to clayey sand*

*Note: Overconsolidated or cemented

Sounding - Shelby County, TN

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0 5 10 15 20 25qt (MPa)

Dep

th B

GS

(m

)

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0 1 2 3 4 5 6 7 8Friction Ratio (%)

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-500 500 1500 2500u2 (kPa)

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0 250 500Vs (m/sec)

SMSilt

Dense Sand

Stiff Clay

Clayey Silt

Dense Sand

CPT-Related Websites

• The Liquefaction Site (and CPT site): www.liquefaction.com

• Link page to manufacturers, suppliers, and CPT services: http://www.usucger.org/insitulinks.html

• Listing of available videos on CPT and other in-situ tests: http://www.geoinstitute.org/in-situ.html

• The book Cone Penetration Testing in Geotechnical Practice (Lunne, Robertson, & Powell, 1997):

• Review: http://geotech.civen.okstate.edu/magazine/books/

• Order: http://www.routledge-ny.com/