STRUCTURAL ENGINEERING

1. UNIVERSITY OF TECHNOLOGY
BUILDING AND CONSTRUCTION DEPARTMENT
GEOTECHNICAL ENGINEERING
Soil Structure Interaction
Soil Constitutive Relation Modeling
-1-
Prepared by
ADNAN NAJEM LAZEM
M.Sc. in Structural Engineering
2012-2013
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2. Soil Structure Interaction
Soil Constitutive Relation Modeling
Introduction to Soil Constitutive Relation Modeling
Soil is a complicated material that behaves :
1. non-linearly and often shows anisotropic.
2. Time dependent behavior when subjected to stresses.
3. soil behaves differently in primary loading, unloading and reloading.
4. It exhibits non-linear behavior well below failure condition with stress
dependent stiffness.
5. Soil undergoes plastic deformation.
6. It is inconsistent in dilatancy.
7. Soil also experiences small strain stiffness at very low strains and upon
stress reversal.
These above general behavior made the soil modeling not possibly being
accounted for in simple elastic-perfectly plastic.
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3. Soil Structure Interaction
Soil Constitutive Relation Modeling
1. MOHR-COULOMB
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4. Soil Structure Interaction
Soil Constitutive Relation Modeling
2. (MODIFIED) CAM-CLAY
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5. Soil Structure Interaction
Soil Constitutive Relation Modeling
3. DUNCAN-CHANG (HYPERBOLIC) MODEL
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6. Soil Structure Interaction
Soil Constitutive Relation Modeling
4. PLAXIS HARDENING SOIL MODEL
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7. Soil Structure Interaction
Soil Constitutive Relation Modeling
5. HYPER-ELASTIC MODEL
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8. Soil Structure Interaction
Soil Constitutive Relation Modeling
6. HYPO-ELASTIC MODEL
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9. Soil Structure Interaction
Soil Constitutive Relation Modeling
7. Visco-Plastic model
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10. Soil Structure Interaction
Soil Constitutive Relation Modeling
A short overview of the Soil Hardening model
Features of the model :
The Hardening Soil model (HS-Standard)
was designed by [2], [3] in order to reproduce basic
macroscopic phenomena exhibited by soils such as:
1. Densification, i.e. a decrease of voids volume
in soil due to plastic deformations.
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11. Soil Structure Interaction
Soil Constitutive Relation Modeling
2. Stress dependent stiffness, i.e. commonly
observed phenomena of increasing stiffness
modules with increasing confining stress
(also related to increasing depth).
3. Soil stress history, i.e. accounting for
preconsolidation effects.
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12. Soil Structure Interaction
Soil Constitutive Relation Modeling
4. Plastic yielding, i.e. development of
irreversible strains with reaching a yield
criterion.
5. Dilatancy, i.e. an occurrence of negative
volumetric strains during shearing.
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13. Soil Structure Interaction
Soil Constitutive Relation Modeling
Soil model with strain hardening behavior:
The plastic strain causes an increase in the yield stress as
shown below. Soils with loosely packed grains are strain
hardening because the disturbance during sharing causes the
grains to move closer together.
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14. Practical applications of the HS model
• Retaining wall excavations
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15. Soil Structure Interaction
Soil Constitutive Relation Modeling
• A short overview of the Softening Soil model
Features of the model :
Most natural clayey deposits, as well as
lime/cement treated clayey soils, exhibit strain-softening
behavior, which can affect, for example, the stability of an
embankment and the bearing capacity of a foundation on
this kind of ground.
Failure of soil under a foundation normally occurs
progressively, and in order to simulate the progressive
failure phenomenon, strain-softening material behavior
should be considered.
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16. Soil Structure Interaction
Soil Constitutive Relation Modeling
• Modeling Strain-softening
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17. Soil Structure Interaction
Soil Constitutive Relation Modeling
• Soil model with strain softening behavior:
The plastic strain causes a decrease in the yield stress as
shown below. Soils with densely packed grains are strain
softening because disturbance during sharing causes the grains
to move apart causing dilation.
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18. Soil Structure Interaction
Soil Constitutive Relation Modeling
• Soil model with Elastic–Perfectly Plastic behavior:
For relatively low-medium risk projects, an assumption
may be made that the stress-strain response can be represented
by two straight lines, to describe an initial linear elastic stiffness
(OA) and the yield stress or strength at failure during plastic
straining (AB).
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19. SUMMARY
Geotechnical engineers often faces challenges to choose
the most appropriate soil model applicable in their numerical
modeling. Therefore, there should be in depth understanding on
the concepts, advantages, limitation and also output of each
model for each problem being modeled.
Engineers should also make use of constitutive model
which provides a reasonable fit to data obtained from range of
laboratory test.
It is important to conduct various computation
measurement comparisons along with additional full-scale
experiments to ascertain the degree of realism in the models in
order to adjust and refine them to each type of different
modeling application.
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20. References
[1] Rafał F. Obrzud, GeoMod Consulting Eng. “On the use of
the Hardening Soil Small Strain model in geotechnical
practice”.
[2] Addenbrooke, T., Potts, D., and Puzrin, A. The influence of
pre-failure soil stiffness on the numerical analysis of the
tunnel construction. Géotechnique, 47(3):693–712, 1997.
[3] Schanz, T., Vermeer, P., and Bonier, P. (1999). Formulation
and verification of the Hardening Soil model. In Beyond
2000 in Computational Geotechnics. Balkema, Rotterdam,
1999.
[4] Kok Sien Ti, et al, “A Review of Basic Soil Constitutive
Models for Geotechnical Application”, EJGE.
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