Influence de la compacité sur la structure des pores et le transport du chlorure dans les terreaux d’infrastructures vertes

Abstract

The overflow of sewers after heavy rainfall represents a challenge for Canadian cities. To address this situation, many cities prioritize directing stormwater towards infiltration infrastructures rather than directly into storm or sanitary sewers. This approach helps reduce peak flows and the amount of water ending up in the sewers. The hydraulic characteristics of the soil used in Montreal's green infrastructures significantly influence the mechanisms of infiltration of rainwater. The main objective of this study is to analyze the response of different types of soils to stormwater runoff in infiltration basins. This analysis focuses on the structure and porosity of soils at different relative compactions, allowing for observation of the types of flow that occur in these materials and their influence on water flow. To achieve this objective, infiltration tests in saturated columns and analyses using X-ray tomography (CT scan) were conducted on two types of soils (mixes 1 and 2 from the city of Montreal) at two relative compactions (75% and 85% of the standard Proctor). The infiltration test results were compared to numerical modeling results obtained with two transport models. The results of the infiltration tests conducted with chloride revealed significant differences in the breakthrough curves of mixes 1 and 2 compared to the reference soil, Bomix sand. With both soil mixes, chloride passed through the column more quickly in terms of the ratio between the volume of water recovered downstream and the total void volume. The numerical results show that the mobile-immobile flow model (MIM), a model suitable for soils with dual porosity and preferential flow paths, better replicates the breakthrough curves than the convective-dispersive model (CD). Increasing the relative compaction from 75% to 85% does not affect this observation. X-ray tomographies visually confirm the existence of dual porosity and the variability of pore size in the soils. The results demonstrate that compaction significantly impacts saturated hydraulic conductivity by reducing the volume of macropores between aggregates.

Date	18 Jun 2024
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	François Duhaime (Supervisor) & Jean-Sébastien Dubé (Co-supervisor)