Geotechnical Site Characterization by Cone Penetration Testingbartlett/CVEEN6330/CPTMayne.pdf ·...
Transcript of Geotechnical Site Characterization by Cone Penetration Testingbartlett/CVEEN6330/CPTMayne.pdf ·...
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/