1454
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
On the other hand the PR’s model clearly shows an
accumulation of vertical displacement at each cycle. Moreover
during the first phase, transient and stationary behaviours can be
distinctly observed. The change in amplitude of loading implies
a change in the tendency of accumulation.
Figure 6. Comparison between mean effective and deviatoric stresses at
0.5m depth under the top of the suction caisson for PR and DP models.
Corresponding evolutions of mean effective and deviatoric
stresses are shown in Figure 6 while pore pressure accumulation
is given in Figure 8. During the first part of the loading, the
difference between both models is limited. For the Prevost’s
model, the transient phase is short and a drop in mean effective
stress is coupled with an increase of pore water pressure. Then a
stationary phase takes place, corresponding to an
accommodation phase (see in Figure 7) and the mean effective
pressure gets back to its first value when pore water pressure
dissipates. The difference is quantitatively greater for the
deviatoric stress but qualitatively the behaviour is identical.
Figure 7. Stress paths in the p’-q plane at 0.5m depth (PR model). The
first step of loading ends after 1000s when the second begins.
During the second part of loading, the soil characterized by
PR model shows a continuous decrease of mean effective stress
without reaching a stationary state. Greater amplitude of loading
entails greater plasticity effects and then contractancy. After
about 1600s, the stress path reaches the phase transformation
line and the mean effective stress increases for a while before
going down again. This continuous contractancy appears
because the model involves plasticity in loading and unloading
as well as a transition between contractive and dilative zones.
On the other hand, the soil described by DP model behaves
elastically most of the time because once the greatest deviatoric
stress is reached, the stress path lies within the plasticity surface
when unloaded and reloaded.
4 CONCLUSIONS
The Prevost’s model is simple, elegant and able to qualitatively
take into account the main features of cyclic loading. Basic
parameters are easy to obtain from classical laboratory tests.
Nevertheless an accurate modelling of cyclic tests requires
additional parameters and a new form of plastic potential.
A suction caisson was modelled as a practical case study.
Capabilities of the Prevost’s model compared with a classical
Drucker-Prager model appear clearly. The transient modelling
depicts pore pressure and plastic deformation accumulation
which the Drucker-Prager model is unable to represent.
Figure 8. Comparison between pore pressure evolutions at 0.5m depth
under the top of the suction caisson for PR and DP models.
5 ACKNOWLEDGEMENTS
I would warmly acknowledge all people that help me daily to
achieve this PhD and my colleagues that suffer my little
idiosyncrasies. I would also thank the FNRS for its financial
support.
6 REFERENCES
Arulmoli, K., et al. 1992.
Verification of Liquefaction Analyses by
Centrigue Studies, Laboratory Testing Program, Soil Data Report. .
Elgamal, Ahmed, et al. 2003. Modeling of cyclic mobility in saturated
cohesionless soils.
Internation Journal of Plasticity.
2003, Vol. 19,
pp. 883-905.
Houlsby, G. T., Ibsen, L. B. et Byrne, B. W. 2005.
Suction caissons for
windturbines.
Perth , Australia : International Symposium on
Frontiers in Offshore Geotechnics (ISFOG).
Ishihara, K., Tatsuoka, F. et Yasuda, S. 1975. Undrained deformation
and liquefaction of sand under cyclic stresses.
Soils and
foundations.
1975, Vol. 15, 1, pp. 29-44.
Popescu, R. et Prevost, J.-H. 1993. Centrifuge validation of a numerical
model for dynamic soil liquefaction.
Soil Dynamics and
Earthquake Engineering.
1993, Vol. 12, pp. 73-90.
Prevost, J.H. 1985. A simple plasticity theory for frictional cohesionless
soils.
Soil Dynamics and Earthquake Engineering.
1985, Vol. 4, 1,
pp. 9-17.
Vertseele, H. 2012.
Cyclic loading of suction caisson foundations for
offshore wind turbines.
University of Liège. 2012. Master Thesis.
Yang, Zhaohui et Elgamal, Ahmed. 2008. Multi-surface Cyclic
Plasticity Sand Model with Lode Angle Effect.
Geotechnical and
Geological Engineering.
June 2008, Vol. 26, 3, pp. 335-348.
Zerfa, F. Z. et Loret, B. 2003. Coupled dynamic elastic-plastic analysis
of earth structures.
Soil dynamics and Earthquake Engineering.
2003, Vol. 23, pp. 435-454.
