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Soil-structure Interaction in Geothermal Foundations

Moradshahi, Aria | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48277 (06)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khosravi, Ali
  7. Abstract:
  8. Regarding the issue that significant amount of energy consumption in the world is dedicated to heating and cooling of the buildings, by using traditional methods of heating and cooling, the environment is facing serious problems like green house gases. There were various techniques for decreasing the amount of contaminants stem from this process. Heat-exchanger energy piles are one of the most common methods that will result in economic usage of energy resources. Assessing the long-term behavior of the energy piles requires comprehensive understanding of the complex interaction between soil and pile subjected to mechanical and thermal loadings. Several numerical and analytical methods have been proposed for the analysis of geothermal heat exchanger energy piles during thermo-mechanical loading, including load transfer (T-z) and finite element method (FEM) formulations. This study adapts the axial load-transfer analysis, originally developed for piles under mechanical loading, to study the interaction between soil and energy piles during combined mechanical loading and thermal volume change. Specifically, this study uses this approach to understand the effect of restrained thermal expansion on the mobilized side shear resistance and the role of head restraint using data from energy piles beneath an actual building during heating. Also a finite difference method was developed to evaluate the thermo-mechanical behavior of the energy piles using FLAC 2D. These analysis were validated using in-situ measurements of the distributions in axial stresses and strains in three instrumented, full-scale energy piles installed beneath a one-story building at the US Air Force Academy in Colorado Springs, CO. After selecting appropriate values of soil, foundation, and soil-structure interaction properties, for both models, they were observed to properly capture the observed distributions in stress and strain during heating and cooling. The main impacts of the boundary conditions are reflected in the nonlinearity of the distribution of the thermal axial stress distribution and the location of the maximum stress. The head stiffness imposed on the pile by the overlying structure was observed to have a major effect on the pile behavior, while the role of lateral expansion on soil-structure interaction was observed to be negligible. The cooling process was not observed to lead to a major change in the pile response from cooling for the particular subsurface stratigraphy at the site, with an elastic response observed in both heating and cooling
  9. Keywords:
  10. Thermal Expansion ; Thermomechanical Loading ; Finite Difference Method ; Load Transfer Method ; Heat Exchangers ; Energy Pile

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