Profiling Overconsolidation Ratio in Clays by Piezocone...
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Transcript of Profiling Overconsolidation Ratio in Clays by Piezocone...
Georgia Tech
Profiling Overconsolidation Ratio in Clays by Piezocone and Flat
Dilatometer Tests
Paul W. Mayne
Georgia Tech
Cavity Expansion-Critical State Model for CPTu-OCR
φ’, Cc, Cs
Soil Properties:M = 6 sinφ’/(3-sinφ’)
φ’ = effective stress friction angleCc = compression indexCs = swelling indexΛ . 1 – Cs/Cc
IR = G/su = UndrainedRigidity IndexG = shear modulussu = undrained shear strength
Georgia Tech
Cavity Expansion-Critical State Model• Cone Tip Resistance: qt- σvo = Nkt su
• Nkt = (4/3) [ ln(IR)+ 1] + π/2 + 1
• su = (M/2) σvo´ (OCR/2)Λ
)/1(
12/)1)(ln3/4('/))(/2(2
Λ
+++
−=π
σσR
vovot
IqMOCR
Georgia Tech
Determine Undrained Rigidity Indexττ = shear stress= shear stress
γγss = shear strain= shear strain
ττmaxmax = s= suu = c= cuu = undrained shear strength= undrained shear strength
ττ //γγss = G= shear modulus= G= shear modulus
Define: Rigidity Index:Define: Rigidity Index:IIRR = G/s= G/suu
γRef = = 1/I1/IRR
Georgia Tech
Cavity Expansion-Critical State Model∆umeas = ∆uoct + ∆ushear
Spherical Cavity Expansion: ∆uoct = (4/3) su ln(IR)CSSM: ∆ushear = σvo´ [1 - (OCR/2)Λ]CSSM: su/σvo' = (M/2)(OCR/2)Λ
)/1(
1)ln()3/2(1)'/(2
Λ
−
−∆=R
vo
IMuOCR σ
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Type 2 Piezocone Model for OCR
∆umeas = ∆uoct + ∆ushear
∆u2 =(2/3M) σvo'(OCR/2)Λ ln(IR) + σvo´[1-(OCR/2)Λ]
qt-σvo = (M/2) σvo'(OCR/2)Λ[(4/3)(lnIR +1)+π/2 +1]
Georgia Tech
Cavity Expansion CPTu2 Model
OCRM
q uT b
vo=
+−
2
1195 1
1
. '
/
σ
Λ
where M = 6 sinφ’/(3-sinφ’) and Λ . 1 – Cs/Cc
fs u2
qc →→ qqTT
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Fixed Wall Chamber Tests
Kaolinitic Clay from SlurryPrestressed in Steel Chambers and Unloaded to atmospheric conditionsExtensive lab testing (consol, triaxial, direct simple shear, Ko-tests)Miniature in-situ tests (electric cone, piezoprobe, vane)
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Fixed-Wall Chamber Testing at Cornell University
Kaolin-silica mixtureLL = 33, PI = 11wn = 34 %Prestressed to 0.5 atms
Chamber: d = 1.5 mH = 2.3 m
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Miniature Cone & Piezoprobe DataChamber Tests with Cornell Clay
0
200
400
600
800
1000
1200
-50 0 50 100 150
Piezocone Readings (kPa)Dep
th (met
ers)
qT
u1
u2
Georgia Tech
Applied & Predicted OCRs in KaolinCornell Clay Chamber Tests
0
200
400
600
800
1000
1200
0 10 20 30 40Overconsolidation Ratio, OCR
Dep
th (met
ers)
CPTu2
Prestress = 50 kPa
Triaxial Tests: φ' = 33.5o Λ = 0.75
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K50 Kaolinitic Clay in Flexible Wall Chamber Tests (Kurup & Tumay, 1993)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 2 4 6 8 10
Overconsolidation Ratio, OCRDe
pth
(m) CPTu Model
Induced
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St. Hilaire, Quebec
0
5
10
15
20
25
30
0 1 2 3 4 5Overconsolidation Ratio, OCR
Dep
th (met
ers)
CPTu
Oedometer
Lafleur et al. (1988, CGJ)φ' = 28o Λ = 0.75
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Taranto, Italy
6
8
10
12
14
16
18
20
22
0 10 20 30 40 50 60Overconsolidation Ratio, OCR
Dep
th (met
ers)
CPTu2
Oedometer
Battaglio, et al. (1986) φ' = 28o Λ = 0.80
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Saint Jean Vianney, QuebecLaRochelle, et al. (1988)
0
1
2
3
4
5
0 20 40 60 80 100OCR
Dep
th (m)
SCE-CSSM
Meas. sp' = 1 MPa
0
1
2
3
4
5
0 1 2 3 4 5Piezocone Reading (MPa)
Dep
th (m)
qt
u2
Georgia Tech
OCR from Type 1 Piezocones
)/1(
1 1'95.1
12Λ
+−=
vo
t uqM
OCRσ
fs u1
qc →→ qqTT
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San Francisco Bay Mud, Muni Metro Station
0
5
10
15
20
25
30
35
40
0 1 2 3 4Overconsolidation Ratio, OCR
Dep
th (met
ers)
CPTu1
Oedometer
Koutsoftas (1989)φ' = 29o Λ = 0.75
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Boston Blue Clay, Massachusetts
Boston Blue Clay
0
10
20
30
40
0 1 2 3 4 5Overconsolidation Ratio, OCR
Dep
th (met
ers)
Oedometer
CPTu1
Baligh et al. (1980)φ' = 33.5o Λ = 0.80
Boston Blue Clay
0
10
20
30
40
0 5 10 15 20
Piezocone Reading (kg/cm2)
Dep
th (met
ers)
qt
u1 (apex)
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Taranto, Italy
6
8
10
12
14
16
18
20
22
0 10 20 30 40 50 60
Overconsolidation Ratio, OCRDep
th (met
ers)
Oedometer
CPTu1
Battaglio, et al. (1986) φ' = 28o Λ = 0.80
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Dual-Element Piezocones and Paired Sets of u1 and u2 Soundings
Georgia Tech
Bothkennar, UK Test Site(Powell, et al., 1988)
0
2
4
6
8
10
12
14
16
18
20
0 1 2 3 4 5 6Overconsolidation Ratio
CPTu1
CPTu2
φ' = 370
Λ = 0.80
0
2
4
6
8
10
12
14
16
18
20
0.0 0.5 1.0 1.5 2.0Piezocone Reading (MPa)
Dep
th (m
eter
s)
qt
u1
u2
Georgia Tech
Dual CPTu - Haga NorwayHaga Clay, Norway
0
1
2
3
4
5
6
7
8
0 5 10 15 20Overconsolidation Ratio, OCR
Dep
th (met
ers)
CPTu1CPTu2Oedometer
Lunne, et al. (1986) φ' = 34o Λ = 0.7
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Brent Cross, UK (London Clay)
0
2
4
6
8
10
12
14
16
18
20
0 10 20 30 40 50 60Overconsolidation Ratio, OCR
Dep
th (met
ers) CPTu1
CPTu2Oedometer
Lunne, et al. (1986) φ' = 20o Λ = 0.75
Georgia Tech
Cavity Expansion-Critical State Method for Flat Dilatometer in Clays
Essentially, the lift-off pressureis dominated by porewater effects
induced during penetration
p0 ≈ umax
Georgia Tech
CPTu-DMT Database: p0 ≈ umeas
Georgia Tech
CE-CSSM for DMT in Clays
Georgia Tech
CE-CSSM for DMT in Clays
Georgia Tech
Conclusions
o Theoretical Basis for relating OCR to normalized CPTu parameter (qt-um)/σvo’ and DMT parameter, KD.
o Cavity Expansion + Critical State Soil Mechanics indicates importance of φ’, Λ = 1 −Cs/Cc, and Rigidity Index, IR
o Calibration with Well-Documented Sites
qc
fsu1
u2
→→ qqTT