DEM Modelling of Unbound Granular Materials for Transport Infrastructures
On soil fabric and rockfill embankments
Time: Tue 2020-08-18 13.00
Subject area: Transport Science, Transport Infrastructure
Doctoral student: Ricardo de Frias Lopez , Jord- och bergmekanik
Opponent: Associate Professor Leena Korkiala-Tanttu, Aalto University, Finland
Supervisor: Professor Johan Silfwerbrand, Betongbyggnad
Unbound granular materials (UGM) are widely used as load-bearing layers and for embankment construction within transport infrastructures. These play a significant role on operation and maintenance of transportation systems. However, pavement and railway engineering still today rely heavily on empirical models based on macroscopic observations. This approach results in limited knowledge on the fundamentals at particle scale dictating the macroscopic response of the material. In this sense, the discrete element method (DEM) presents a numerical alternative to study the behaviour of discrete systems with explicit consideration of processes at particulate level. Additionally, it allows obtaining information at particulate level in a way that cannot be matched by traditional laboratory testing. All of this, in turn, can result in greater micromechanical insight.This thesis aims at contributing to the body of knowledge of the fundamentals of granular matter. UGM for transport infrastructures are studied by means of DEM in order to gain insight on their response under cyclic loading. Two main issues are considered: (1) soil fabric and its effect on the performance of coarse-fine mixtures and (2) modelling of high rockfill railway embankments. Among the main contributions of this research there is the establishing of a unified soil fabric classification system based exclusively on force transmission considerations that furthermore correlates with performance. In particular, fabrics characterized by a strong interaction between the coarse and fine fractions resulted in improved performance. A soil fabric type with a potential for instability was also identified. Regarding embankments, DEM modelling shows that traffic induced settlements accumulate on the top layers and therefore seem to be unaffected by embankment height above a certain value. A marked influence of degradation, even considering its nearly negligible magnitude, was observed, largely resulting in increased settlements.