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Numerical Investigation of the Effects of Different Parameters on the Mechanical Response of Energy Pile under Cyclic Thermal Loading in Saturated Clay

Sadeghzadeh, Mohammad Reza | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55594 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ahmadi, Mohammad Mehdi
  7. Abstract:
  8. Considering the environmental pollution caused by the consumption of fossil fuels, replacing clean and renewable energies instead of fossil fuels has become one of the most critical issues across the world. The use of energy geostructures, especially energy piles, to exchange the heat between the superstructures and the ground is one of the approaches for taking advantage of clean energy. In order to maintain the safety and the serviceability of structures built on energy piles, it is necessary to study the effects of heat exchange between energy piles and the ground on the mechanical behavior of energy piles, as well as the effects of various parameters on the interaction between energy piles and the ground. In this thesis, a 3D finite difference model was initially created using FLAC3D for thermo-mechanical analysis of energy piles under thermal loading and coupled thermo-mechanical loading. The current numerical model has been verified by comparing the results of the present model with those of field tests and numerical models performed by other researchers. Then using the present model, the effects of changing the thermal conductivity coefficient of energy pile and clayey soil, the thermal expansion coefficient of energy pile and clayey soil, and the amount of thermal loading applied to the energy pile on the mechanical response of the energy pile have been investigated under cyclic heating and cooling thermal loading. In this research, mechanical responses include axial strain and stress, shaft friction, and axial displacement along the pile. The results indicate that under applying ±20°C of temperature change, only increasing the pile thermal expansion coefficient leads to large displacements in the soil and the pile, and as a result, by returning the pile to the initial temperature, the soil prevents the energy pile from returning to its initial state Also, the results show that the change of the thermal expansion coefficient of the pile and the amount of thermal loading compared to the other investigated parameters more significant effects on the mechanical behavior of the energy pile. Considering the amount of tensile stress developed along the energy pile and the low tensile strength of concrete, for designing energy piles under thermal loading, cooling periods are more important than heating ones. Since energy piles are often subjected to mechanical compressive load in addition to thermal load, in this research, the effects of changing the amount of mechanical load on the energy piles mechanical behavior have also been investigated. The results show that increasing compressive mechanical load during the cooling of the energy pile increases the contraction strains along the pile, and due to the interaction between the pile and the ground, the soil strains increase too. As a result, by returning the energy pile to the initial temperature, the ground prevents the energy pile from returning to its initial state. Also, the compressive mechanical load increases the compressive stress and decreases the tensile stress along the pile, as a result, the possibility of tensile rupture of the concrete energy pile during cooling is eliminated.
  9. Keywords:
  10. Energy Pile ; Parametric Study ; Energy Pile Group ; Coupled Thermo-Mechanical Behaviour ; Saturated Soil ; Numerical Finite Difference Modeling ; Cyclic Thermal Loading

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