[Translate to English:] Thèse : L’impact des événements climatiques et de la sécheresse sur le phénomène du retrait gonflement des argiles en interaction avec les constructions

PhD defense: Hossein ASSADOLLAHI

Title: The impact of climatic events and drought on the shrinkage and swelling phenomenon of clayey soils interacting with constructions

Team: GC-E

Abstract: Climate change and severe climatic events such as long drought/rehydration periods are at the origin of the shrinkage and swelling phenomenon in expansive soils. This phenomenon is affected by Soil-Vegetation-Atmosphere (SVA) interactions and can cause severe structural damage to lightly loaded constructions such as residential buildings. The objective of this research work is to simulate the in-situ behavior of the shrinkage-swelling in expansive soils in a SVA context using numerical tools. A soil-atmosphere interaction method is primarily presented along with a coupled hydro-thermal soil model. This approach was established in order to determine primarily, the natural time variable boundary conditions at the considered soil surface based on the mass and energy balance concept, and secondly to determine the spatial-temporal changes of the soil suction, water content and temperature. This approach was validated using in situ observations of monitored sites. Thereafter, the influence of the water uptake by vegetation was incorporated in the source term of the unsaturated water flow theory, using an existing root water uptake model. Subsequently, the temporal variations of the soil suction were related to the volume change behavior using a simple approach developed based on the experimental results of drying/wetting tests performed in the literature. The associated volumetric indices in the void ratio-log suction plan, along with the complementary parameters of the linear model were correlated with basic geotechnical parameters. The proposed approach was validated with in situ data provided from an experimental site. The Roaillan experimental site was instrumented in order to monitor the soil’s physical changes along with the structural behavior of the building. Comparisons between the simulated and observed soil suction, soil water content, temperature and soil movements in time and depth showed an acceptable performance of the predictions. The approach was then extended to study the influence of future climate projections (2050) on the soil’s physical variables and movements. Three RCP climate change scenarios were considered in this analysis which revealed different possible behavior in both short term and long term. Finally, the developed approach was applied to the French territory by dividing it to six different climatic regions. Different soil parameters were attributed to each of these climatic regions in order to set the reference condition. Thereafter, the influence of different external factors was analyzed on the soil movements over a chosen period. The study finally suggests the adequate actions to take for minimizing the amplitude of the shrinkage and swelling phenomenon in a SVA context.

The jury is composed of:

• Mrs Farimah MASROURI, Professor, University of Lorraine (ENSG) – Reviewer
• Mrs Mahida HATTAB, Professor, Université de Lorraine – Examinator
• Mr Yu-Jun CUI, Professor, Ecole des Ponts ParisTech – Reviewer
• Mr Jean-Marie FLEUREAU, Professor, Centrale Supélec (ECP) – President of Jury
• Mr Hossein NOWAMOOZ, Associate Professor, INSA Strasbourg – PhD director

The defense will be held on Monday, 17th June 2019 at 15:00 pm in the amphitheater "Arts et Industries" of INSA Strasbourg.

Keywords: Drought, Shrinkage-Swelling of clayey soils, Soil-Vegetation-Atmosphere interactions, climate change, suction, unsaturated expansive soils, Geotechnical modelling, Geotechnical monitoring