Transcript Determination of Soil Stiffness Parameters

Determination of Soil Stiffness
Parameters
Short Course on Computational Geotechnics + Dynamics
Boulder, Colorado
January 5-8, 2004
Stein Sture
Professor of Civil Engineering
University of Colorado at Boulder
Contents
General concepts and stiffness of sand
Hooke’s law
E-moduli from triaxial testing
E-moduli from oedometer testing
Examples on the estimation of E
Stiffness of clays
Undrained clay behavior
Drained clay behavior
Examples on the estimation of E
Computational Geotechnics
Determination of Soil Stiffness Parameters
Idealized and real stressstrain behavior of soils
Idealized types of stress-strain behaviors: (a) nonlinear elastic
Model, (b) linear elastic model, and (c) elastoplastic model
Computational Geotechnics
Determination of Soil Stiffness Parameters
Idealized and real stressstrain behavior of soils
Various types of elastoplastic behaviors: (a) strain hardening, (b)
perfectly plastic, (c) strain softening, and (d) combination of a to c.
Computational Geotechnics
Determination of Soil Stiffness Parameters
Hooke’s Law of Isotropic
Elasticity
Computational Geotechnics
Determination of Soil Stiffness Parameters
Hooke’s Law of Isotropic
Elasticity
Computational Geotechnics
Determination of Soil Stiffness Parameters
Standard Drained Triaxial Test on
Sand
Computational Geotechnics
Determination of Soil Stiffness Parameters
Standard Drained Triaxial Test on
Sand
Computational Geotechnics
Determination of Soil Stiffness Parameters
Oedometer Test on Sand
Computational Geotechnics
Determination of Soil Stiffness Parameters
Oedometer Test on Sand
Computational Geotechnics
Determination of Soil Stiffness Parameters
Oedometer Test on Sand
Hooke:
1 
2
E
(1  2 ) Eoed  Eoed
1 
3
Loose:
E
2
 150
ref
p
3
Dense:
Computational Geotechnics
E
2
 500
ref
p
3
y
p
ref
(  13 )

y
p
ref
Determination of Soil Stiffness Parameters
Oedometer Test on Sand
 'y 
 'x
K0
 2 'x
Loose:
x
x
E
2
 150
2
 150 ref
ref
ref
p
3
p
p
Dense:
x
x
E
2

500

2

500
p ref
3
p ref
p ref

This implies:
Computational Geotechnics
E  E 50
Determination of Soil Stiffness Parameters
Summary on Stiffness Parameters:
Sand
(Laboratory based experience)
2
E  E 50  E oed
3
Loose:
  13
E

150
ref
p 
p
'
x
ref
E

Dense:

 500
ref
p
p
'
x
ref
pref 100kPa
 Computational Geotechnics
EE
ref
Loose: E  15MPa
 'x
pref

Dense: E  50MPa
 'x
pref
 'x
pref
Unloading: About 4 times stiffer.  small

Determination of Soil Stiffness Parameters
Selection of Moduli for FEM-Computation
Example 1 (loading):
Layer 1 (extremely loose sand
Mohr-Coulomb model:
/
Layer 1:  y0  70kPa 
Average

Computational Geotechnics
 'y  95kPa
ref
E 50
 15MPa
 'y  50kPa
 'x  50kPa

E 50 15000
0.5 10000kPa
Determination of Soil Stiffness Parameters
Selection of Moduli for FEM-Computation
Example 2 (unloading):
Layer 1 (dense): E 50  45MPa
ref
Unloading:
Layer 3 (medium):
Eurref  4E50ref ,  0.15
for both layers

Mohr-Coulomb
model:
Layer 1:
  2 1.5  55kPa
'
y
'
E  4  45000
Layer 3:

Computational Geotechnics
 'x 10kPa
27.5
100
E 50ref  30MPa

 'x  27.5kPa
 95000kPa
E  4  30000 0.10  38000kPa

Determination of Soil Stiffness Parameters
Eoed from Cone Penetration Test in
Sands
Cone Resistance:
qc
Correlation: E oed  qc
Literature
 NC-Sand:  = 1 to 3

Vermeer’s
Experience:  = 3
Alternatively: Eoed  (30  10) qc p ref
Computational Geotechnics
Determination of Soil Stiffness Parameters
Undrained Triaxial Test on
Clay
15000Cu
Ip%
Normally consolidated clay:
E u50 
Cu = undrained shear strength (or Su)
E u50  3G50
Computational Geotechnics

Determination of Soil Stiffness Parameters
Idealized and real stress-strain
behavior of soils
Computational Geotechnics
Determination of Soil Stiffness Parameters
Idealized and real stress-strain
behavior of soils
Computational Geotechnics
Determination of Soil Stiffness Parameters
Plate Loading Tests
Duncan & Buchignani (1976)
Computational Geotechnics
Determination of Soil Stiffness Parameters
Plate Loading Tests
Computational Geotechnics
Determination of Soil Stiffness Parameters
Summary on Stiffness Parameters:
Clay
Undrained Conditions
Do not use empirical relationships only. Get good quality experimental data from lab tests, cone
penetration tests and vane tests
Computational Geotechnics
Determination of Soil Stiffness Parameters
Drained Behavior for Clays
Computational Geotechnics
Determination of Soil Stiffness Parameters
Drained Behavior for Clays
Computational Geotechnics
Determination of Soil Stiffness Parameters