geotechnical site characterization by cone penetration testing
DESCRIPTION
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) - PowerPoint PPT PresentationTRANSCRIPT
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
0
4
8
12
16
20
24
28
0 20 40 60 80 100
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
0
4
8
12
16
20
24
28
0 20 40 60
qt (MPa)
De
pth
(m
ete
rs)
0
4
8
12
16
20
24
28
0 500 1000
fs (kPa) u b (kPa)
0
4
8
12
16
20
24
28
-200 0 200 400 600 800
qt
ub
fs
Comparison CPT and SPTDowntown Memphis
0
4
8
12
16
20
24
28
0 20 40 60 80 100
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
0
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
0
4
8
12
16
20
24
28
32
36
0 10 20
qt (MPa)
Dep
th (
m)
0
4
8
12
16
20
24
28
32
36
0 100 200 300
fs (kPa)
0
4
8
12
16
20
24
28
32
36
-100 400 900 1400
U2, U0 (kPa)
0
4
8
12
16
20
24
28
32
36
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
0
5
10
15
20
25
0 5 10 15 20 25qt (MPa)
Dep
th B
GS
(m
)
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8Friction Ratio (%)
0
5
10
15
20
25
-500 500 1500 2500u2 (kPa)
0
5
10
15
20
25
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/