Modeling of hydro-chemo-mechanical behavior of clay soils for prediction of landslide displacements

The present thesis is composed of two parts. The first part presents the chemo-mechanical effect on the volumetric and shearing behaviour of saturated soil as a continuum. The second part presents the chemo-mechanical effect on the shearing behaviour of a discontinuity. Following Gajo and Loret, 2003, saturated soil is considered as a two-phase deformable porous medium, namely solid and fluid phase consisting of different species. There are clay particles, adsorbed water and ion in the solid phase. The fluid phase includes pore water and salt which may diffuse through the porous medium. In addition, water may be exchanged between solid and fluid phases while the mass of clay particles and ions in the solid phase remains constant. Thus, the balance equations are momentum balance, the mass balance of pore water and salt in the fluid phase, the mass balance of absorbed water. A two-dimensional element is proposed to approximate the solution of the balance equations which has been implemented in a user-defined subroutine (UEL) of the commercial code ABAQUS. This element has taken into account the 2D displacement of the soil skeleton, multidimensional flow of water, osmotic effect, advection and diffusion of salt. A new hyperelastic law is presented by extending the chemo-mechanical model proposed by Loret et al., 2002. The innovative aspects of the proposed model are the following: 1) both the tangent shear stiffness and bulk stiffness depend on the applied stress state and pore water solution, 2) the anisotropy of fabric tensor is introduced in the elasticity law. Moreover, the yield function has been modified to obtain smaller peak strength for highly overconsolidated samples to have better agreement with experimental results. The proposed 2D model is validated with experimental results on natural bentonite (a very active clay) and the soil extracted from low activity clay of Costa della Gaveta slope in Southern Italy. The swelling and swelling pressure of these two types of soil have been computed and compared with the experimental data to show the accuracy and reliability of the proposed model. Furthermore, the effects of elastic anisotropy are investigated on the soil behaviour such as swelling, swelling pressure, stress paths and horizontal stress. Furthermore, a simplified analysis has been performed to show the effect of swelling pressure on slope stability. In the second part, a contact element is proposed to account for the flow of water and diffusion of salt in addition to displacement in the simulation of interface behaviour. This element has been implemented in a user-defined subroutine (UEL) of ABAQUS. Moreover, a nonlinear elasticity law is proposed in which traction in the contact region has been taken into account. The Mohr-Columb yield criterion is used for the plastic regime in which it is assumed that the friction angle is a function of salt concentration and displacement rate based on the experimental data. Some preliminary results are shown for the flux of salt and water through the element. In addition, the effects of salt concentration and displacement rate are presented on the shearing behaviour of the contact element.