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Determination of Soil Stiffness Parameters

Short Course on Computational Geotechnics + DynamicsBoulder, ColoradoJanuary 5-8, 2004

Stein StureProfessor of Civil EngineeringUniversity of Colorado at Boulder

Contents

General concepts and stiffness of sandHooke’s law

E-moduli from triaxial testing

E-moduli from oedometer testing

Examples on the estimation of E

Stiffness of claysUndrained clay behavior

Drained clay behavior

Examples on the estimation of E

Computational Geotechnics Determination of Soil Stiffness Parameters

Idealized and real stress-strain behavior of soils

Idealized types of stress-strain behaviors: (a) nonlinear elasticModel, (b) linear elastic model, and (c) elastoplastic model



Various types of elastoplastic behaviors: (a) strain hardening, (b)

perfectly plastic, (c) strain softening, and (d) combination of a to c.


Hooke’s Law of Isotropic Elasticity


Hooke’s Law of Isotropic Elasticity


Standard Drained Triaxial Test on Sand


Standard Drained Triaxial Test on Sand


Oedometer Test on Sand





Hooke:

Loose:

Dense:

oedoed EEE3

2)21(

1

1

( 13)

ref

y

ref pp

E

3

2150

ref

y

ref pp

E

3

2500



y'

x'

K0

2 x'

refx

refx

ref ppp

E

15023

2150

refx

refx

ref ppp

E

50023

2500

E E50

Loose:

Dense:

This implies:


Summary on Stiffness Parameters: Sand

(Laboratory based experience)

E E50 2

3Eoed

13

E

pref150

x'

pref

E

pref500

x'

pref

E E ref x

'

pref

E 15MPa x

'

pref

E 50MPa x

'

pref

pref 100kPa

Loose:

Dense:

Loose:

Dense:

Unloading: About 4 times stiffer. smallComputational Geotechnics Determination of Soil Stiffness Parameters

Selection of Moduli for FEM-Computation

E50ref 15MPa

y0

/ 70kPa

y' 50kPa

y' 95kPa

x' 50kPa

E50 15000 0.5 10000kPa

Layer 1 (extremely loose sand

Layer 1:

Average

Mohr-Coulomb model:

Example 1 (loading):


Selection of Moduli for FEM-ComputationExample 2 (unloading):

E50ref 45MPa

E50ref 30MPa

15.0,4 50 refrefur EE

y' 21.5' 55kPa

x' 27.5kPa

E 4 45000 27.5100 95000kPa

x' 10kPa kPaE 3800010.0300004

Layer 1 (dense): Layer 3 (medium):

Unloading: for both layers

Mohr-Coulomb model:

Layer 1:

Layer 3:


Eoed from Cone Penetration Test in Sands

qc

Eoed qc

= 1 to 3

= 3

refcoed pqE )1030(

Cone Resistance:

Correlation:

Literature NC-Sand:

Vermeer’s Experience:

Alternatively:


Undrained Triaxial Test on Clay

Eu50

15000CuIp%

Eu50 3G50

Normally consolidated clay:

Cu = undrained shear strength (or Su)






Plate Loading Tests

Duncan & Buchignani (1976)


Plate Loading Tests


Summary on Stiffness Parameters: ClayUndrained Conditions

Do not use empirical relationships only. Get good quality experimental data from lab tests, cone penetration tests and vane tests


Drained Behavior for Clays


Drained Behavior for Clays
