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Physical Modeling of Energy Pile Behavior under Thermo-Mechanical Loading

Arbab, Ali | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53225 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Jafarzadeh, Fardin
  7. Abstract:
  8. A heat exchanger pile is a pile that is equipped with absorber pipes so that it can exchange heat with the surrounding soil. These piles couple the structural support role of conventional piles to the heat exchanger role of shallow geothermal systems for any built environment. So They are subjected to both mechanical and thermal loads. The use of these piles can be useful in reducing greenhouse gas emissions and reducing fossil fuel consumption. In order to study the thermomechanical behavior of heat exchanger piles, a physical model has been constructed in the Advanced Soil Mechanics Laboratory of the School of Civil Engineering at Sharif University of Technology. In this physical model, four closed-end aluminum pipes with a diameter of 20 mm and a length of 600 mm are used as pile models, and each pile is equipped with a U-shaped pipe to circulate water inside the pile. The space between the absorber pipe and the pile is filled with water to have the same temperature throughout the pile. Besides, a water bath is used to control and change the temperature, which is equipped with a water circulation system. In this model, 16 temperature sensors are used, 12 of which are embedded around the pile and inside the soil, also these 12 sensors are able to measure soil moisture. Four other sensors are used to measure the temperature of the pile, the temperature of the water entering the pile, the water temperature coming out of the pile, and the temperature of the soil tank. Also, in this model, 128 strain gauges are used along with the pile on its outer surface; in a way, that strain gauges are installed on four sections in each pile. The sections are 10, 30, 40, and 55 cm apart from the top of the pile. At each section, eight strain gauges are used, 4 of which are used to measure axial strain, and four other strain gauges are used to measure bending strain. Besides, LVDTs are used to measure the head settlement of each pile. In this physical model, the total pressure cells are also used to monitor the vertical and horizontal pressure changes of the soil under the toe pile. Two series of experiments have been performed to study the mechanical and thermal behavior of heat exchanger piles. In the first series of experiments, three experiments (T1 to T3) were conducted to study the effect of heating and cooling cycles with three different mechanical loads on energy piles. In the second series of experiments, three experiments (T4 to T6) were performed to investigate the effect of increasing and decreasing the pile's temperature on the settlement and the bearing capacity of the pile. The results show that the thermal cycles cause permanent settlement in a pile, which decreases with the increasing number of cycles. Also, increasing the temperature of the pile increases the bearing capacity, and reducing its temperature reduces the bearing capacity of the pile. Also, heating the pile creates more axial force than cooling it. Regarding the method of heat transfer, it can be said that during thermal loading, the heat transferred from the pile radially expands more sharply than the depth, and the amount of temperature changes in the points under the pile is tiny compared to around the pile
  9. Keywords:
  10. Heat Exchanger Pile ; Single Pile ; Physical Modeling ; Geothermal Energy ; Thermomechanical Loading ; Energy Pile

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