Les sols argileux peuvent presenter des variations importantes de volume lors d'un changement hydrique, tel une periode de secheresse. Ce phenomene de retrait-gonflement des sols argileux est a l'origine de nombreux prejudices aux bâtis ce qui le situe, apres les inondations, au second rang des aleas naturels francais en matiere de cout des dommages : 5 milliard d'euros entre 1988 et 2007. Les maisons individuelles sont les plus touchees par ce phenomene qui provoque un tassement differentiel du bâti a l'origine de sa degradation (fissures dans les elements de maconnerie non armee en particulier). L'objectif de cette these est d'etudier la vulnerabilite des bâtis vis-a-vis de l'alea retrait-gonflement a travers une analyse de l'interaction sol-structure. Ce travail s'est porte sur les trois grands volets suivants : le comportement hydromecanique des sols argileux, l'interaction sol-structure et l'evaluation des dommages structuraux. Le comportement hydromecanique des sols argileux a ete modelise par le concept de surface d'etat et integre dans un modele d'interaction sol-structure inspire du modele de Winkler, avec des approches de plus en plus complexes : cas unidimensionnel tout d'abord, 2D ensuite en assimilant la structure a une poutre, puis en 3D en representant la structure par une plaque. Ces modeles d'interaction sol-structure permettent de calculer la deflexion relative d'un bâti, en fonction d'une valeur de succion imposee et des proprietes mecaniques ou hydromecaniques de la structure et du sol d'assise. La deflexion relative du bâti est alors comparee a des valeurs seuils afin d'evaluer le dommage. La derniere partie de cette these consiste en une etude de faisabilite pour le developpement de courbes de vulnerabilites adaptees a la problematique du retrait gonflement. Ces courbes representent la moyenne des dommages d'un type de bâti concu sur un type de sol gonflant pour une valeur de succion imposee. Ces courbes ont ete developpees a partir d'une typologie des sols gonflants et d'une typologie des bâtis issue des bases de donnees des maisons sinistrees. La moyenne des dommages est calculee par la methode de Monte-Carlo, en prenant en compte la variabilite des parametres du bâti.

Phénomènes d'interaction sol-structure vis-à-vis de l'aléa retrait-gonflement pour l'évaluation de la vulnérabilité des ouvrages

Prediction of Shear Strength and Vertical Movement due to Moisture Diffusion through Expansive Soils. (August 2006) Xiaoyan Long, B.S., Changsha Railway University; M.S., Tongji University Co-Chairs of Advisory Committee: Dr. Charles Aubeny Dr. Robert Lytton This dissertation presents an investigation of engineering behavior of expansive soils. An analytical study was undertaken for the development and modification of a Windows-based two-dimensional finite element computer program FLODEF that performs a sequentially coupled flow-displacement analysis for the prediction of moisture diffusion and the induced volume change in soils supporting various elements of civil infrastructure. The capabilities of the model are illustrated through case studies of shear strength envelope forecast and parametric studies of transient flow-deformation prediction in highway project sites to evaluate the effectiveness of engineering treatment methods to control swell-shrink deformations beneath highway pavements. Numerical simulations have been performed to study the field moisture diffusivity using a conceptual model of moisture diffusion in a fractured soil mass. A rough correlation between field and the laboratory measurements of moisture diffusion coefficients has been presented for different crack depth patterns.

Prediction of shear strength and vertical movement due to moisture diffusion through expansive soils

Settlements of lightly loaded structures are frequently caused by changes in matric suction causing shrinkage or swelling of soils. These structures are often not designed to deal with influences of these changes. This study explores issues related to ground displacement due to changes in matric suctions induced by root wateruptake by tree. Numerical simulations of moisture migration patterns in the unsaturated zone and in the vicinity of established tree were performed. The moisture flow model used is based on Richard’s equation with incorporated sink term and integrated with appropriate water-uptake models in 2D and 2D axi-symmetric form. The numerical solution was derived from a finite element approach for spatial discretisation along with a finite difference time-marching scheme. A series of numerical simulations have been performed by the model to assess functionality of stress-deformation analysis partially coupled to flow equation. The model is capable of estimating matric suction changes and accompanying volume change profiles due to water-uptake over a full-annual cycle. Time dependent boundary conditions based on rainfall data effects have also been explored. Results of sensitivity and parametric analyses shows that the predicted ground displacements are sensitive to all the parameters tested. On the other hand, all initial time step sizes used for testing the convergence criterion on the simulation works was found to converge and the simulated results shows difference of not more than ±5 %, which is considered satisfactory. The research also provides an assessment of the significance of trees induced suction changes on unsaturated soil slopes. The model is capable of estimating ground displacements due to matric suction changes on sloping ground. The magnitude of the ground displacement on the sloping surface depends on the relative position of trees on the slope. A relatively straight forward simple approach to model the matric suction changes and accompanying volume change profiles beneath tree as a result of water-uptake has been developed. The resulting model is potentially valuable for a range of geotechnical engineering problems situated on the vadose zones containing trees.

Tree-induced deformation in unsaturated soils

Effect of Ionic Stabilization on Vertical Movement in Expansive Subgrade Soils in Texas

The shrinkage-swelling behavior of the foundation layer in the urban perimeter of the city of Smara (Morocco), results in defects observed in the walls and partitions of public buildings, individual homes and city infrastructures. Since the shrinkage-swelling phenomenon is long-lasting and evolves slowly over time, these defects reappear, even after the damage has been repaired. The present study deals with the lithological, mineralogical and geotechnical characterization of the soil, with the aim of improving our understanding of the origins of its swelling characteristics and thereby adopting the necessary measures to limit the future appearance of defects in constructions. Granulometric analysis and determination of the Atterberg limits in the laboratory revealed that the clay fraction of the mudstone has only a weak potential to swell, which is insufficient to explain the soil's tendency to expand. X-ray diffractometry, together with the examination of several samples under a scanning electron microscope, revealed the presence of sulfate minerals (gypsum and anhydrite), which are known to experience significant changes in volume when hydrated or dehydrated. This soil's tendency to expand thus has its origins mainly in the transformation process of anhydrite into gypsum and vice versa, as a function of variations in its water content. Determination of the pressure modulus, the pressure yield point and the swelling pressure, based on in situ pressuremeter and rigid plate tests, allowed the deformability and state of rupture of the studied soil to be characterized. The measured values of swelling pressure are considerably greater than those transmitted to the ground by the foundations of existing

/pdf/damage-to-foundations-from-swelling-soil-in-smara-morocco-12i3otf3c3.pdf

Damage to foundations from swelling soil in Smara (Morocco): geotechnical data and mitigation measures

: Damage to lightly loaded structures, paving and service piping in areas of expansive clay soils has occurred throughout the world. The cause of this damage has been the inability to accurately model expansive soil movement so that foundations are adequately designed to withstand the movement. The amount and rate of differential soil movement for expansive soils is due to a combination of soil characteristics, namely: suction compression index, unsaturated permeability, and diffusivity. Currently, geotechnical engineers run tests to measure the soil properties required to estimate differential soil movements. However, there seems to be apprehension toward attempting these soil movement calculations due to the perceived complexity of the calculations or a simple lack of understanding of the theory. The procedures delineating the step by step process used to calculate suction profiles and volume strains of expansive soils is presented. These procedures include the methodology to predict soil heave and shrink underneath shallow foundations which generate maximum center lift and maximum edge lift slab distortion modes. The main contributions of this research are: equations and procedures to calculate the equilibrium suction profile and depth to constant suction for a particular soil profile and location, equations to calculate the horizontal velocity flow of water in unsaturated soils, the methodology to predict differential soil movement shortly after a slab has been constructed and before the soil under the slab has reached an equilibrium moisture content, and the procedures to apply differential soil movement theory to soil profiles with multiple layers and moisture effect cases to be used for shallow foundation design.

Procedures to Predict Vertical Differential Soil Movement for Expansive Soils

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Procedures to Predict Vertical Differential Soil Movement for Expansive Soils