2 Material Properties and Test Program

AVERTISSEMENT Ce document est le fruit d'un long travail approuvé par le jury de soutenance et mis à disposition de l'ensemble de la communauté universitaire élargie. Il est soumis à la propriété intellectuelle de l'auteur. Ceci implique une obligation de citation et de référencement lors de l’utilisation de ce document. D'autre part, toute contrefaçon, plagiat, reproduction illicite encourt une poursuite pénale. Contact : [email protected] LIENS Code de la Propriété Intellectuelle. articles L 122. 4 Code de la Propriété Intellectuelle. articles L 335.2- L 335.10 http://www.cfcopies.com/V2/leg/leg_droi.php http://www.culture.gouv.fr/culture/infos-pratiques/droits/protection.htm "' UNIVERSITÉ 3 ~ DE LORRAINE L.ABORATOIRE O ' ~TUOE DES MICROSTRUCTURES ET DE M~CANtQUE • DES MATéRIAUX Dissertation presented to obtain the doctor' s degree of: Université de Lorraine by: Qian-Feng GAO Speciality: GeotechnicaJ Engineering Micro-macro approach of dilatancy phenomenon in remoulded clays - Study of the behaviour under saturated and unsaturated conditions Defended on December 13, 2018 In front of the jury: Philippe Cosenza Professor Université de Poitiers Reviewer Pierre Delage Professor Ecole des Ponts ParisTech Reviewer Cristina Jommi Professor Delft University ofTechnology Examiner Zhenyu Yin MCF-HDR Ecole Centrale de Nantes Examiner Mohamad Jrad MCF Université de Lorraine Examiner Lamine Ighil Ameur Doctor Cerema de Blois Examiner Mahdia Hattab Professor Université de Lorraine Supervisor Université Paris Saclay Jean-Marie Fleureau Professor Co-supervi sor CentraleSupélec Laboratoire d'Étude des Microstructures et de Mécanique des Matériaux LEM3 UMR CNRS 7239 - Université de Lorraine 7 rue Félix Savart - F-57070 Metz - France ~ UNIVERSITÉ m3 1.ABORATOlRE DES \? o·ûuoe MlCROSTRUCTURES ~~h,G\ ~ DE LORRAINE ET DE M~CANIOUE DES MATÊRIAUX Thèse pour• l'obtention du Grade de: Docteur de l'Université de Lorraine Présentée par: Qian-Feng GAO Spécialité: Géotechnique Approche micro-macro du phénomène de dilatance dans les argiles remaniées - Etude du comportement en condition saturé et non saturé Soutenue le 13 décembre 2018 Devant le jury composé de : Philippe Cosenza Professeur Université de Poitiers Rapporteur Pierre Delage Professeur Ecole des Ponts ParisTech Rapporteur Cristina J ommi Professeur Delft University of Technology Examinateur Zhenyu Yin MCF-HDR Ecole Centrale de Nantes Examinateur Mohamad Jrad MCF Université de Lorraine Examinateur Lamine Ighil Ameur Docteur Cerema de Blois Examinateur Mahdia Hattab Professeur Université de Lorraine Directeur de thèse Université Paris Saclay Jean-Marie Fleureau Professeur Co-directeur de thèse CentraleSupélec Laboratoire d'Étude des Microstructures et de Mécanique des Matériaux LEM3 UMR CNRS 7239 - Université de Lorraine 7 rue Félix Savart - F-57070 Metz - France Acknowledgements Acknowledgements This dissertation was carried out at the laboratory of LEM3 of the University of Lorraine, in Metz, France, from 2015 to 2018. It was financed by the China Scholarship Council (CSC) (No. 201508430168). I have received great help from many people during the preparation and writing of the dissertation. I would like to take this opportunity to thank them. First of all, I would like to sincerely thank my supervisor Prof. Mahdia Hattab for her valuable expertise and patient guidance. I am extremely grateful for her enthusiastic encouragement and help, which enable me to overcome all the problems I faced during the course of experiments and the preparation of the dissertation. I would like to express my deepest thanks to my co-supervisor Prof. Jean-Marie Fleureau at CentraleSupélec, whose excellent guidance, precious ideas and useful advice have greatly contributed to the accomplishment of my doctoral research. Besides my supervisors, I am very grateful to the jury members Prof. Philippe Cosenza at Université de Poitiers, Prof. Pierre Delage at Ecole des Ponts ParisTech, Prof. Cristina Jommi at Delft University of Technology, Prof. Zhenyu Yin at Ecole Centrale de Nantes, Dr. Mohamad Jrad at Université de Lorraine and Dr. Lamine Ighil Ameur at Cerema de Blois for their insightful comments and constructive suggestions to improve my dissertation. I am very grateful for the technical assistance provided by Dr. Mohamad Jrad in unsaturated triaxial tests and X-ray microtomography scans. The results and specimens of saturated triaxial tests offered by Dr. Lamine Ighil Ameur are also highly appreciated. I would like to thank Prof. Zhenyu Yin for his recommendation, otherwise I would not have the opportunity to meet with my current excellent supervisors. My special thanks are also extended to Prof. Pierre-Yves Hicher at Ecole Centrale de Nantes for his invaluable advice in interpreting the macro-micro results of saturated clays. I would like to express my great appreciation to my Master’s supervisors, Prof. Hui Dong at Xiangtan University and Prof. Zongwei Deng at Hunan City University, who encouraged me to start the doctoral research and have given me continued support. I Micro-macro approach of dilatancy phenomenon in remoulded clays-Study of the behaviour under saturated and unsaturated conditions I take this opportunity to express my sincere gratitude to all the faculty members of the LEM3 laboratory, particularly, Mr. Hanbing Bian, Ms. Wen Chen, Mr. Guillaume Robin, Ms. Yudong Zhang, Mr. Olivier Perroud, Mr. Jean-Sébastien Lecomte and Mr. Jérôme Slowensky, for their kind help and technical assistance. I would like to express my sincere gratitude to my colleagues and friends especially Dr. Dan Zhao, Mr. Zhengtian Yang, Mr. Wenqing Cheng, Dr. Yajun Zhao, Dr. Jing Wen and Mr. Lizhao Dai for their helps in performing unsaturated triaxial tests, soil-water characteristic tests and scanning electron microscopy observations. Last but not least, I must extend my warmest and most sincere thanks to my family and my girlfriend for providing me with continued support and encouragement throughout the three years of my study in France. Qian-Feng GAO Metz, France September 15, 2018 II Abstract Abstract Clay is extensively distributed on the Earth’s surface. It is widely used in the field of Civil Engineering, for example, as a building material. Furthermore, clay can be used as not only a natural barrier in the dam cores but also a matrix for the storage of radioactive wastes because of its desired retention properties. The complex nature of clay has aroused great interest of researchers in its mechanical behaviour under saturated and unsaturated conditions. The microscopic observation is a necessary complement for a better understanding of this behaviour. The objective of this research is to examine the influence of triaxial stress paths on the mechanical behaviour of remoulded clay and the mechanisms that occur at the microstructural level. The dilatancy phenomenon is particularly investigated considering a given stress level reached by following different stress paths. In the second part, this research focuses on the influence of suctions on the mechanical behaviour. For the saturated remoulded clay, the dilative behaviour at a given stress level, reached by following two different stress paths (i.e., the constant σ'3 stress path and the purely deviatoric stress path), was analysed in detail. The influence of stress levels was also examined in this research. The microstructural analysis was conducted at different scales by means of different methods: scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and X- ray microtomography (XR-μCT). The macroscopic results of saturated clay show that, at a given stress level, the volumetric behaviour greatly depends on the stress path. In the case of overconsolidated clay, the dilatancy is activated especially when triaxial shearing is performed following the purely deviatoric stress path. At the microscopic level, the results highlight five modes of particle orientation that could be activated under triaxial loading. The results also reveal that the appearance of dilatancy phenomenon in highly overconsolidated remoulded clay may be attributed to the tortuous arrangement of clay particles, the opening of micropores, and the formation and opening of mesocracks. For the unsaturated remoulded clay, the studies were performed through many macroscopic and mesoscopic tests on Kaolin K13 clay (the same material as that for saturated tests) and a III Micro-macro approach of dilatancy phenomenon in remoulded clays-Study of the behaviour under saturated and unsaturated conditions kaolinite-montmorillonite mixture termed M35 (to show the influence of mineralogy). The evolution of suctions was measured using hygrometers placed near the upper and lower ends of clay specimens. The results show that, at a high suction level, the deviatoric stress of unsaturated clay increases to a peak and then decreases down to a residual value. The shear strength of unsaturated clay generally increases with increasing mean stress and suction. However, in the high suction tests, the development of cracks during drying led to the inhomogeneity of the specimens and thus resulted in relatively small shear strengths. Keywords: Remoulded Clay; Triaxial Test; Dilatancy; Microstructure; Suction; Shear Strength IV Résumé Résumé L’argile est abondamment distribuée à la surface de la Terre, c’est un matériau très largement utilisé dans la domaine Génie Civil, comme matériaux de construction par exemple. L’argile est également utilisée comme des barrières naturelles dans les cœurs

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