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Water infiltration associated with natural precipitation events or other artificial activities such as pipe leaks in expansive soils significantly influence the engineering properties; namely, coefficient of permeability, shear strength and volume change behavior. For this reason, it is challenging to design or construct geotechnical infrastructure within or with expansive soils. Several billions of dollars losses, world-wide, can be attributed to the repairing, redesigning and retrofitting of infrastructure constructed with or within expansive soils, annually. Piles are widely used as foundations in expansive soils extending conventional design procedures based on the principles of saturated soil mechanics. However, the behavior of piles in unsaturated expansive soils is significantly different from conventional non-expansive saturated soils. Three significant changes arise as water infiltrates into expansive soil around the pile. Firstly, soil volume expansion contributes to ground heave in vertical direction. Secondly, volume expansion restriction leads to development of the lateral swelling pressure resulting in an increment in the lateral earth pressure in the horizontal direction. Thirdly, pile-soil interface shear strength properties change due to variations in water content (matric suction) of the surrounding soil. These three changes are closely related to matric suction variations that arise during the water infiltration process. For this reason, a rational methodology is necessary for the pile load transfer mechanism analysis based on the mechanics of unsaturated soils. Studies presented in this thesis are directed towards developing simple methods to predict the load transfer mechanism changes of piles in expansive soils upon infiltration. More emphasis is directed towards the prediction of the pile mechanical behavior which includes the pile head load-displacement relationship, the pile axial force (shaft friction) distribution and the pile base resistance using unsaturated mechanical as a tool. The function of matric suction as an independent stress state variable on the mechanical behavior pile is highlighted. More specifically, following studies were conducted: (i) Previous studies on various factors influencing the load transfer mechanisms of piles in unsaturated expansive soils are summarized and discussed to give a background of current research. More specifically, state-of-the-art reviews are summarized on the application of piles in expansive soils, mobilization of lateral swelling pressure, mobilization of unsaturated pile-soil interface shear strength and methods available for the load transfer analysis of piles in expansive soils. (ii) Employing unsaturated soil mechanics as a tool, theoretical methods are proposed for estimating the lateral earth pressure variations considering the mobilization of lateral swelling pressure. The proposed methods are verified using two large-scale laboratory studies and two field studies from published literatures. (iii) The shear displacement method and load transfer curve methods used traditionally for pile load transfer mechanisms analysis for saturated soils were modified to extend their applications for unsaturated expansive soils. The influence of volume change characteristics and unsaturated soil properties on unsaturated expansive soils are considered in these methods. The validation of the modified shear displacement method and modified load transfer curve method were established using a large-scale model test performed in the geotechnical engineering lab of University of Ottawa and a field case study results from the published literature. (iv) A large-scale model pile infiltration test conducted in a typical expansive soil from Regina in Canada in the geotechnical lab of University of Ottawa is presented and interpreted using the experimental data of volumetric water content suction measurements and shear strength data. The results of the comprehensive experiment studies are also used to validate the proposed modified shear displacement method and modified load transfer curve method achieving reasonable good comparisons. The proposed modified shear displacement method and modified load transfer curve method are simple and require limited number soil properties including the soil water characteristic curve (SWCC), matric suction profile upon wetting and drying and some soil physical properties. Due to these advantages, they can be easily and conveniently applied in engineering practice for prediction of the mechanical behavior of piles in unsaturated expansive soils, which facilitate practicing engineers to produce sound design of pile foundation in unsaturated expansive soils in a simplistic manner.

Master of Science / Department of Civil Engineering / Dunja Peric / Piles have been used for many years in civil infrastructure as foundations for buildings, bridges, and retaining walls. Energy piles are thermo-active foundation systems that use geothermal energy for heating and cooling of buildings. Ground source heat is a very attractive, economical, efficient and sustainable alternative to current heating practices. Unlike the air temperature, the temperature below the Earth’s surface remains relatively constant throughout the year, somewhere between 10oC to 15oC below a depth of 6 m to 9 m (Kelly, 2011). This provides an opportunity for construction of thermo-active foundation systems with embedded geothermal loops. The main purpose of such thermo-active system is to transfer deep ground heat to a building through the fluid circulating within the geothermal loop. It is because these thermo-active foundation systems enable heat exchange between the deep ground and the building that is called the heat exchanger pile (HEP). The thermal energy supplied by a HEP can then supplement air-pump-based heating/cooling system. Although heat exchanger piles have been successfully implemented in Europe and Asia, their usage in U.S. remains uncommon. One reason for this might be currently limited understanding of the associated soil-structure interaction, thus unfavorably affecting the design procedures. To this end, a study was undertaken to investigate the predictive capabilities of computational models and to gain a better understanding of the load-transfer mechanisms of energy piles. Thus, coupled thermo-hydro-mechanical computational modeling of a single actual end bearing HEP was carried out for different loading scenarios including thermal and mechanical loads by using the finite element code ABAQUS/Standard 6.13-2. The results of the analyses of the heat exchanger pile with two different types of layered soil profile are presented: isotropic and anisotropic. The computational model was validated and verified successfully against field test results for all considered loading scenarios. Additional analyses were performed to gain a deeper insight into the effects of soil layering and on the behavior of energy piles. It was found that changes in the soil stiffness affected primarily the head displacement and vertical stresses and strains in the pile.

Soft soil reinforcement by inclusion is a growing technique caracterized by a pile grid and a granular embankment introduced between the reinforced soil and the structure. Unlike traditionnal methods, the load is partially transferred to the pile heads by arching in the embankment. The application area of this research focuses on the shallow foundations case, in which the thickness of the embankment is small. The litterature review shows that only a few studies were dedicated to that case, and that fundamental questions remains concerning the load transfer in the embankment. Chosen method for this research consists in two-dimensionnal physical modelling, analysis of the conducted simulations, and development of an analytical model in order to predict the load transfer to the piles by arching in the embankment. The results of this PhD thesis provide original elements of evidence of the load transfer in the studied system, proposes an analytical model based on block division of the granular embankment by shear bands - which is in good agreement with experimental data - and lead to a better understanding of arching in soils.

Soft soil reinforcement by inclusion is a growing technique caracterized by a pile grid and a granular embankment introduced between the reinforced soil and the structure. Unlike traditionnal methods, the load is partially transferred to the pile heads by arching in the embankment. The application area of this research focuses on the shallow foundations case, in which the thickness of the embankment is small. The litterature review shows that only a few studies were dedicated to that case, and that fundamental questions remains concerning the load transfer in the embankment. Chosen method for this research consists in two-dimensionnal physical modelling, analysis of the conducted simulations, and development of an analytical model in order to predict the load transfer to the piles by arching in the embankment. The results of this PhD thesis provide original elements of evidence of the load transfer in the studied system, proposes an analytical model based on block division of the granular embankment by shear bands - which is in good agreement with experimental data - and lead to a better understanding of arching in soils. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished