Hossein Nowamooz

On désigne habituellement par retrait-gonflement des sols argileux les variations de volume qu’un massif d’argile peut subir sous l’effet des variations de la pression interstitielle négative (succion) de l’eau, lors d’une humidification ou d’un séchage. L’objectif de ce travail est de compléter les connaissances expérimentales sur le comportement hydromécanique des sols gonflants rencontrés dans les travaux de génie civil, de géotechnique et de géotechnique de l’environnement afin de mieux en tenir compte dans les modèles de calcul. De nombreux travaux ont montré l'intérêt de réaliser des essais œdométriques pour caractériser le potentiel et la cinétique de gonflement des sols. Ils ont révélé également l’influence de l’humidification ou du séchage sur le gonflement ou le retrait, avec des pertes ou des augmentations de rigidité des éprouvettes. En revanche, l’influence de plusieurs cycles de séchage/humidification sur le comportement mécanique n’a été que très rarement analysée. Cette thèse rapporte les résultats d’études expérimentales effectuées à l’œdomètre avec imposition de succion par la méthode osmotique sur des matériaux gonflants compactés lâches et naturels denses. Plusieurs cycles de séchage/humidification ont été appliqués sur ces matériaux sous trois faibles charges mécaniques constantes. Pendant ces cycles, les éprouvettes manifestent un retrait cumulé pour le sol lâche et un gonflement cumulé pour le sol dense. Les résultats montrent que dans les deux cas, les déformations volumiques convergent vers un état d’équilibre où le sol présente un comportement réversible. A la fin des cycles de succion, un cycle de chargement/déchargement a été effectué sous les succions constantes. Les valeurs de la pression de préconsolidation p0(s), de l’indice de compression vierge [lambda(s]] et de l’indice de compression élastique [kappa] dépendent directement des chemins de contrainte suivis. L’ensemble des résultats expérimentaux permet de déterminer les surfaces de charge : la limite de séparation de micro/macro (Lm/M) ; la surface de chargement-effondrement (LC : Loading Collapse du modèle BBM) et la surface de comportement saturé (SCS). La succion limite entre la micro- et la macrostructure (Lm/M) dépend parfaitement de la structure interne et du diamètre qui délimite les deux familles de pores. L’évolution de la pression de préconsolidation en fonction de la succion imposée est présentée par la surface LC. Les courbes de compressibilité sous différentes succions convergent vers la courbe correspondant à l’état saturé sous de fortes contraintes appliquées. La pression à partir de laquelle, le sol continue son chemin sur la courbe du comportement normalement consolidé est appelée la pression de saturation (Psat). Plus la succion imposée est élevée, plus la charge nécessaire pour atteindre cette pression de saturation est importante. La surface SCS présente la variation de la pression de saturation en fonction de la succion imposée. Nous pouvons considérer que les surfaces de charge SCS et LC sont uniques pour les sols denses cependant elles se superposent à la fin des cycles de succion pour les sols lâches. Les cycles hydriques augmentent aussi la limite (Lm/M) entre la micro- et la macrostructure pour les deux sols

Increasing extreme weather events and climate change can significantly affect soil moisture regimes, particularly soil suction, leading to additional challenges associated with unsaturated soils, including the collapse phenomenon. The collapsibility of soils poses significant engineering and geotechnical risks globally, necessitating urgent attention from engineers. This work establishes a numerical model of a shallow foundation subjected to rainfall and load using COMSOL Multiphysics. A hydromechanical model (H-M) is introduced which incorporates The Richards’ module and the Extended Basic Barcelona Model (EBBM) as a constitutive model to predict settlements in shallow foundations influenced by climate change and intense rainfall. The validation of the model is conducted through experimental tests, ensuring its accuracy. Additionally, in the practical application, the hydromechanical model is applied to anticipate the effect of infiltration on settlements of shallow foundations. The simulation results show that infiltration leads to an increase in the pressure head above the water table, decreasing soil suction, which induces additional settlement due to wetting-induced collapse. The maximum settlement happened at the corners of the footing due to increased exposure to infiltration and a greater reduction in suction. The collapse potential calculated from the numerical simulation was found to be consistent with the predictions established via analytical models, validating the accuracy of the numerical approach.

This work investigates the equilibrium stage of the crack propagation of a fine-grained soil after several drying and wetting cycles (shrinkage and swelling hysteresis). This stage is found to be crucial in practical engineering since the soil continues to show its irreversible hydraulic settlement, which is a potential risk for some severe structural damages. The shrinkage area and the shrinkage crack area were determined by using the image processing method. For the cyclic experimental investigations, the shrinkage cracks were followed during six months of successive wetting and drying cycles for two samples (with two different initial water contents). These long-term tests were completed by some short term single drying path tests performed on samples prepared at different initial states. The results showed the existence of a unique equilibrium stage at the end of the wetting and drying cycles for the two studied samples. The equilibrated soil subsidence was separated into two parts: the reversible settlement of the equilibrium stage and the irreversible settlements cumulated during successive wetting and drying cycles. At the equilibrium stage, the reversible deformation was 5.9% and the irreversible deformation was 3.8%. A simplified theoretical approach was also used to predict the cracking equilibrium stage and its soil subsidence. The fitted parameters of the theoretical approach for each cycle were stabilized to confirm the existence of this equilibrium stage.

Borehole heat exchanger (BHE) array is a key element in the ground source heat pump system (GSHPS). The BHE array is traditionally simplified by assuming the same heat exchange rate for each BHE, which normally is not correspondent to the real applications. In this investigation, a TRT was firstly conducted for a site located in Shanxi Province (China) to get the local ground thermal properties. A numerical simulation framework was next verified by the TRT results. Subsequently, the ground thermal properties obtained by the TRT were used in the numerical simulation model to investigate the influence of two operation strategies on the ground temperature development of the surrounding soil and the BHE performance. The results showed that both ground temperature and BHE array performance decreased during the 8-year operation period of the BHE array in the heating mode. The ground temperature around the center BHE was lower in the same heat load (SHL) scenario (same heat load for the BHEs in the array) than in the same inlet temperature (SIT) scenario (same carrying fluid inlet temperature for the BHEs in the array), and this difference can be 2 C in the 7^th year. The annual average outlet temperature in the SHL scenario was also lower than that in the SIT scenario, especially in the long term. The investigation shows that SIT working strategy superiors the SHL strategy, providing a reference for the upcoming investigation on the design aspect of the GSHPS.

Waterproof capacity, thermal isolation, and pushover strength are the main characteristics when an unstabilized rammed earth (URE) wall is constructed. In this paper, a comprehensive numerical simulation model is built to evaluate the effect of 15 different factors on those three aforementioned properties of URE walls. The simulation results show that the hydraulic, thermal, and mechanical properties of the wall are interconnected. It is found that the waterproof capacity of the wall can be mainly improved by increasing the dry density, decreasing the rising damp effect, and reducing the fine content value of the wall. The thermal insulation characteristic of the wall can be ameliorated by increasing the wall thickness and reducing the rising damp effect, fine content, and dry density. In addition, the pushover capacity of the wall can be strengthened by increasing the wall width, fine content, wall thickness, and vertical load and decreasing the rising dampness and wall height. In addition, time has a positive effect on the waterproof capacity, thermal insulation, and mechanical strength of URE walls. These properties change significantly in the first 100 days and then stabilize after 180 days for a typical URE wall. Eventually, a new theoretical approach is proposed to predict the long-term THM behavior of URE walls by considering the 15 factors in its framework.

Borehole Heat Exchanger (BHE) can be installed in different infrastructures to store or extract energy, such as pavement cooling in summer and de-icing in winter. Although there are approaches to estimating the performance of a BHE based on analytical, semi-analytical or numerical simulation methods, predicting the performance of a BHE in the perspective of Machine Learning (ML) is still necessary. In this investigation, four ML algorithms including Linear Regression (LR), Polynomial Regression (PR), Artificial Neural Network (ANN) and Random Forest (RF) were used to explore the underlying relationship between the Heat Extraction Rate (HER) and the influencing factors. In total, the annual HERs of 400 Thermal Performance Tests (TPTs) covering 12 major factors were computed in a validated numerical simulation framework. After providing necessary database, the 4 ML approaches were trained and evaluated. The results showed that the trained PR approach had the best performance. Specifically, the trained PR approach had a Root-Mean-Square Error (RMSE) lower than 1.74 W · m⁻¹, with the Coefficient of Determination (R²) higher than 0.99. Additionally, the trained approach was compared to an in-situ TPT in Shijiazhuang (China) and two numerical simulated scenarios in Alsace (France). The results showed that the trained PR approach predicted well the in-situ TPT by having 3 W · m⁻¹ of RMSE, and it predicted correctly the numerical simulated HER of a BHE with 0.09 and 0.72 W · m⁻¹ of RMSEs for two scenarios with 5 and 1 °C of inlet fluid temperatures. The proposed prediction model can be applied to estimate the performance of a BHE, providing another option to fast evaluate the BHE performance.

In this article, a simplified soil-atmosphere interaction analysis is proposed by using a simple mass/water balance equation and a thermal based energy balance approach which gives the infiltration rate and the soil surface temperature respectively. The deduced surface temperature is primarily validated by comparison with field measurements (Héricourt site) and secondly by comparing the derived net solar irradiance to seven net irradiance models. Finally, a hydro-thermal simulation approach established by relating the variations of the soil water content to the soil thermal conductivity, is applied to the Roaillan site, which was monitored since 2011 to investigate the hydro-thermal changes of the soil due to environmental stresses in the vicinity of the foundation of a damaged building. The simulation results provide the necessary data to determine the affected depth of the soil due to climatic conditions. Results show that the first layer (< 1.5 m depth) is mainly affected by climatic conditions in which the variations of water content and suction are less than those of temperature. Furthermore, the soil settlements are also compared to the extensometer measurements at three different depths. Although some differences exist but globally the proposed approach is able to consider the soil-atmosphere interaction in its framework.

Granular materials are often used in pavement structures. The influence of anisotropy on the mechanical behaviour of granular materials is very important. The coupled effects of water content and fine content usually lead to more complex anisotropic behaviour. With a repeated load triaxial test (RLTT), it is possible to measure the anisotropic deformation behaviour of granular materials. This article initially presents an experimental study of the resilient repeated load response of a compacted clayey natural sand with three fine contents and different water contents. Based on anisotropic behaviour, the non-linear resilient model (Boyce model) is improved by the radial anisotropy coefficient γ₃ instead of the axial anisotropy coefficient γ₁. The results from both approaches (γ₁ and γ₃) are compared with the measured volumetric and deviatoric responses. These results confirm the capacity of the improved model to capture the general trend of the experiments. Finally, finite element calculations are performed with CAST3M in order to validate the improvement of the modified Boyce model (from γ₁ to γ₃). The modelling results indicate that the modified Boyce model with γ₃ is more widely available in different water contents and different fine contents for this granular material. Besides, based on the results, the coupled effects of water content and fine content on the deflection of the structures can also be observed.