The Concept of Effective Stress in Unsaturated Soils - Multiscale Geomechanics: From Soil to Engineering Projects - page 175

capillary pressure may lead to precocious failure phenomena that need to be handled
by introducing a damage criterion into the constitutive law.
Many studies have been carried out in the past 20 years to extend the use of the
effective stress concept to unsaturated soils. The use of the effective stress concept
allows a unified interpretation of the data, both in elasticity and on the failure
criterion. The micromechanical model, which features a single parameter R , leads to
a very good agreement with the experimental results for the determination of both
the q ( p' ) and E (σ' v ) functions.
With the generalized definition of the effective stress proposed in this chapter,
sum of the total stress and the capillary pressure derived from the micromechanical
model, it is possible to regroup all the final points of large strain triaxial tests on the
failure criterion of the saturated samples and those of the small strain triaxial tests on
the master curve of the dry and quasi-saturated specimens. Therefore, this model
constitutes a very practical and simple way of predicting the strength and stiffness of
a soil whenever its capillary pressure is known.
6.7. Acknowledgements
The authors would like to thank the ICCTI, the French Embassy in Portugal
and the CNRS in France for their support in the organization of the exchanges
between the IST and the ECP and for the realization of some of the tests in both
institutions.
6.8. Bibliography
[BIA 89] B IAREZ J., F LEUREAU J.M., I NDARTO T AIBI S., Z ERHOUNI M.I., “Influence of water
negative pore pressure on the flow of granular materials in silos”, Proceedings of the First
International Conference on Micromechanics of Granular Media , Clermont-Ferrand, 4-8
September 1989. B IAREZ J. & G OURVÈS R. (eds), A.A. Balkema, Rotterdam, The
Netherlands, pp. 385-392, 1989.
[BIA 88] B IAREZ J., F LEUREAU J.M., Z ERHOUNI M.I., S OEPANDJI B.S., “Variations de volume
des sols argileux lors de cycles de draînage-humidification”, Rev. Franç. Géotechnique ,
vol. 41, pp. 63-71, 1988.
[BIA 93] B IAREZ J., F LEUREAU J.M., T AIBI S., “Constitutive model for unsaturated granular
media made up by spheres”, Proc. 2nd Int. Conf. on Micromechanics of Granular Media ,
Birmingham, UK, Thornton (ed.), Balkema, Rotterdam, the Netherlands, pp.51-58, 1993.
[BIA 94] B IAREZ J., F LEUREAU J.M., T AIBI S., “Critère de résistance maximale des sols non
saturés : Approche expérimentale et modélisation”, Proc. 13th Int. Conf. on Soil Mech.
and Found. Eng. , New Delhi, Oxford & I.B.H., pp. 385-388, 1994.