Geotechnical Site Characterization by Cone Penetration Testing

Paul W. Mayne, PhD, P.E.Professor Geosystems Professor, Geosystems Civil & Environmental

Engineering

Mid A i FHWAMid-AmericaEarthquake Center

FHWA

Standard Penetration Test63.5-kg DropHammerHammerRepeatedlyFalling 0.76 mAnvil

Rotary-drilledB h l

Split-Barrel

Borehole

p(Drive) Sampler: O.D. = 50 mm I.D. = 35 mm L = 760 mm

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

Representative SPT Profile

Downtown Memphis

SPT N (bpf)

0

4

0 20 40 60 80 100

SPT-N (bpf)

1982 B1

Soil Profile

Fill4

8

ters

)

1982-B3

1982-B5

Silty Sand

Sandy12

16

Dep

th (m

et Silt

Gravelly Sand

20

24

D Desiccated OC Clay

Clayey Sand

OC Cl28

OC Clay Gravelly Sand

Corrections to SPT N-value

Effect Variable Term Value

Overburden Stress

σvo' CN (Pa/σvo')0.5 but < 2

Energy Ratio1

· Safety Hammer· Donut Hammer· Automatic Hammer

CE 0.6 to 0.850.3 to 0.60.85 to 1.0

Borehole Diameter

· 65 to 115 mm· 150 mm

CB 1.001 05Diameter 150 mm

· 200 mm1.051.15

Sampling Method

· Standard sampler· Sampler without liner

CS 1.01.1 to 1.3

Rod · 10 m to 30 m CR 1.0Length · 6 to 10 m

· 4 to 6 m· 3 to 4 m

R 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 SER < 100% with average ER = 60% in the U.S.

N60 ≈ CE CB CS CR Nmeas = Estimated corrected N60 E B S R meas

(N1)60 = CN N60 = Energy-Corrected SPT Value normalized to an effective overburden stress of onenormalized to an effective overburden stress of one atmosphere: (N1)60 = (N60)/(σvo’)0.5 with stress given in atm. (Note: 1 atm = 1 bar = 100 kPa = 1 tsf).g ( )

Cone PenetrometersCone Penetrometers

Electronic Steel Probes with 60° Apex TipASTM D 5778 ProceduresHydraulic Push at 20 mm/sNo Boring, No Samples, No Cuttings, No SpoilContinuous readings of stress friction pressureContinuous readings of stress, friction, pressure

Cone Penetration Tests (CPT)

Cone Trucks

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

Corrections to CPT

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

• Sleeve Friction correction for porewater U l d pressures – Use equal end areas on

friction sleeveB li ti Obt i b f & • Baseline corrections – Obtain before & after sounding

Anchored Cone Rig

Mud Island, Downtown Memphis, TN

6-tonne Geostar truck with 20-tonne hydraulic

hi tpushing system

No special license

Twin earth anchors

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

CPT Profile, Downhole Memphis

0

0 20 40 60

qt (MPa)0 500 1000

fs (kPa) u b (kPa)

-200 0 200 400 600 8000

4

0

4

0

4

8

12(met

ers)

8

12

8

12fs16D

epth

16

20

16

20

fs

20

24

20

24

20

24

ub

28 28 28qt

Comparison CPT and SPTDowntown Memphisp

SPT-N (bpf) and qc (MPa)

Soil Profile

0

4

0 20 40 60 80 100

1982 B1Silty Sand

Fill

8

12ters

)

1982-B31982-B5CPT-qc (MPa)

Silty Sand

SandySilt12

16

Dep

th (m

et Silt

Gravelly Sand

20

24

D

Desiccated OC Clay

Clayey Sand

28 OC Clay

Gravelly Sand

Seismic Piezocone TestSeismic Piezocone Test

VsObtains Four Independent Measurements with Depth:

fsCone Tip Stress, qtPenetration Porewater Pressure u fs

u

Penetration Porewater Pressure, uSleeve Friction, fsArrival Time of Downhole Shear

W t

60ou1

u2Wave, ts

qc

Downhole Shear Wave Velocityy

Anchoring SystemA t t d SAutomated SourcePolarized WaveDownhole VDownhole Vs

Automated Seismic Source

• Electronically-actuated

Automated Seismic Source

• Self-contained

• Left and right l i tipolarization

• Modified beam uses fin to enhance shear wave generation

• Successfully tested to depths of 20mdepths of 20m

• Capable of being used with traditional impulse hammerhammer

0.08 Left Strike

Downhole Shear Waves

-0.02

0

0.02

0.04

0.06

0 50 100 150 200Am

plitu

de Right Strike

CROSSOVER Method

Left Strike

-0.08

-0.06

-0.04 Time (ms)

A

0 08

CROSSOVER Method

-0 02

0

0.02

0.04

0.06

0.08

0 50 100 150 200Am

plitu

de

Shear Wave at 8.15 m

Shear Wave at 9.20 m

-0.08

-0.06

-0.04

-0.02 0 50 100 150 200Time (ms)

A

500500 Maximum crosscorrelation at ∆t = 6.75 ms

CROSSCORRELATION

0

100

200

300

400

200 150 100 50 0 50 100 150 200-100

0

100

200

300

400

-5 0 5 10 15 20

Shear wave velocity = 155 m/s

-400

-300

-200

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

-400

-300

-200

100

Time shift (ms)

Sod Farm, Charleston, SC

00 10 20

qt (MPa)

00 100 200 300

fs (kPa)

0-100 400 900 1400

U2, U0 (kPa)

00 400 800

Vs (m/s)

4

8

4

8

4

8

4

8

12

16

m)

12

16

12

16

12

16

20

24

Dep

th (m

20

24

20

24

20

2424

28

32

24

28

32

24

28

32

24

28

3232

36

32

36

32

36

32

36

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

00 5 10 15 20 25

qt (MPa)

00 1 2 3 4 5 6 7 8Friction Ratio (%)

0-500 500 1500 2500

u2 (kPa)

00 250 500

Vs (m/sec)

0

5

0

5

0

5

0

5

SM

Dense Sand

Clayey Silt

10

BG

S (m

)

10 10 10

Dense Sand

15

Dep

th B

15 15 15Stiff Clay

20

25

20

25

20

25

20

25

CPT-Related Websites

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

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

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

• 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/