Abstract
This paper includes a presentation of a numerical model for the description of the behavior of unsaturated sandy soils under cyclic loading with particular attention for liquefaction. The model is developed within the framework of the theory of Biot and the formulation of Coussy. It is also based on laboratory observations. The formulation leads to a simplified model, which allows also to deal with saturated soils. The cyclic elastoplastic constitutive model “MODSOL” is used to describe the cyclic behavior of the soil. The paper presents an analysis of the influence of the soil saturation on the response of a sandy soil to both monotonic and cyclic undrained loading paths. It shows that the decrease in the saturation degree of a sandy soil leads to an important increase in their resistance to liquefaction.
1. Introduction
Soil liquefaction constitutes a major cause of damage induced by earthquakes. It results from the interaction between the liquid and solid phases in porous media. This phenomenon may occur in both saturated and unsaturated soils; it results from a reduction in the effective mean stress, which leads to a deterioration in both the strength and stiffness of soils. Previous researches in liquefaction concerned mainly saturated soils. Since unsaturated soils are frequently encountered in geotechnical engineering [1], it is of major interest to investigate the soil liquefaction under partially saturated conditions. Triaxial cyclic tests on unsaturated Hostun sand indicated the possibility of liquefaction of partially saturated soils [2] and showed an increase in the resistance to liquefaction of soils with the decrease in the saturation degree.
6. Conclusion
This paper includes the presentation of a simple numerical model for the description of the response of unsaturated sandy soils to cyclic loading with a particular interest in liquefaction. The model is based on the theory of Biot and the formulation of Coussy together with the hypothesis of low suction, zero air flux and immiscible interaction between pore-water and pore-air in sandy soils. This model is similar to that of U-P model and thus it is very easy in using and integrating into finite element program. Numerical simulations conducted with this model showed that the soil saturation degree largely affects the resistance of sandy soils to liquefaction. The presence of pore-air reduces the excess pore pressure generation rate. And the induced partial saturation could mitigate liquefaction.
