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

Georgia Tech

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

Georgia Tech

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)

Georgia Tech

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

Georgia Tech

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

Georgia Tech

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

Georgia Tech

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

Georgia Tech

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

Georgia Tech

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

Georgia Tech

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

Georgia Tech

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)

Georgia Tech

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

Georgia Tech

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

Georgia Tech

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