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Mid-America Earthquake Center. Geotechnical Site Characterization by Cone Penetration Testing. Paul W. Mayne, PhD, P.E. Professor, Geosystems Civil & Environmental Engineering. FHWA. Standard Penetration Test. Rotary-drilled Borehole. Standard Penetration Test (SPT)

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geotechnical site characterization by cone penetration testing

Mid-America

Earthquake Center

Geotechnical Site Characterization by Cone Penetration Testing

Paul W. Mayne, PhD, P.E.

Professor, Geosystems

Civil & Environmental Engineering

FHWA

standard penetration test
Standard Penetration Test

Rotary-drilled

Borehole

Standard Penetration Test (SPT)

Procedures: ASTM D 1586

N = measured Number of Blows to drive sampler 300 mm into soil.

corrections to spt n value

Effect

Variable

Term

Value

Overburden

Stress

svo'

CN

(Pa/svo')0.5 but < 2

Energy

Ratio1

·        Safety Hammer

·        Donut Hammer

·        Automatic Hammer

CE

0.6 to 0.85

0.3 to 0.6

0.85 to 1.0

Borehole Diameter

·        65 to 115 mm

·        150 mm

·        200 mm

CB

1.00

1.05

1.15

Sampling

Method

·        Standard sampler

·        Sampler without liner

CS

1.0

1.1 to 1.3

Rod

Length

·        10 m to 30 m

·        6 to 10 m

·        4 to 6 m

·        3 to 4 m

CR

1.0

0.95

0.85

0.75

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

Corrections to SPT N-value

1 Obtain by energy measurement per ASTM D4633

corrections to spt n value1
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
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
Cone Penetration Tests (CPT)

Cone Trucks

Mobile 25-tonne rigs with

enclosed cabins to allow

testing under all weather

conditions

corrections to cpt
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
Anchored Cone Rig

Mud Island, Downtown Memphis, TN

  • 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
seismic piezocone test
Seismic Piezocone Test

Vs

fs

u2

u1

qc

Obtains Four Independent

Measurements with Depth:

  • Cone Tip Stress, qt
  • Penetration Porewater Pressure, u
  • Sleeve Friction, fs
  • Arrival Time of Downhole Shear
  • Wave, ts

60o

downhole shear wave velocity
Downhole Shear Wave Velocity
  • Anchoring System
  • Automated Source
  • Polarized Wave
  • Downhole Vs
automated seismic source
Automated Seismic Source
  • 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
downhole shear waves
Downhole Shear Waves

Left Strike

Right Strike

CROSSOVER Method

Shear Wave at 8.15 m

Shear Wave at 9.20 m

CROSSCORRELATION

Maximum crosscorrelation at Dt = 6.75 ms

Shear wave velocity = 155 m/s

Time shift (ms)

cpt soil behavioral classification
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 – sand

2 – Organic material 6 – Sandy silt to silty sand 10 – Gravelly sand to sand

3 – 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

cpt related websites
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/