Approche par éléments discrets des sols granulaires. Application à l'analyse des pressions latérales des terres.

Abstract

This thesis presents a contribution to the analysis of lateral earth pressures in different states; at rest, passive and acti ve. The analysis concerns a granular deposit in the dry state, and is carried out using 2D discrete element numerical modeling. In this work, the grains are modeled by circular elements with the introduction of a rolling resistance, the normal contact forces are calculated by a viscoelastic model and the tangential forces are calculated by a viscoelastic model with sliding taking into account the stick-slip phenomenon. The first part of this analysis deals with lateral pressure at rest, for which a model of a cyclic odometer test is developed. It is shown that the evolution of the lateral earth pressure coefficient 𝐾0 with loading history is in good agreement with that of empirical formulas derived from experience, where 𝐾0 increases with the increase of soil’s overconsolidation ratio. Furthermore, micromechanical analysis has shown that for a normally consolidated sample, horizontal contacts are more dominant, and consequently horizontal friction forces are higher, resulting in a low value of 𝐾0. For an overconsolidated sample, vertical contacts become more frequent, increasing horizontal normal forces and leading to an increase in 𝐾0. Using a simple three-grain model, it is highlighted that the evolution of 𝐾0 along a loop for a loading-unloading cycle in the oedometer test results from friction. The second part concerns the analysis of lateral earth pressure in both passive and active states. A model of a granular deposit supported by a rigid moving wall is developed. The obtained results have shown that, for the passive state, the lateral earth pressure coefficient at peak (Kₚ) matched the value obtained from Rankine's equation using the peak friction angle derived from a conventional biaxial compression test. Whereas, for the active state, the lateral earth pressure coefficient (Kₐ) matches the coefficient predicted by Rankine's equation if the introduced internal friction angle is derived from shear tests with stress path similar to that of the active lateral pressure state.