Investigation Into The Thermo-mechanical Performance Of Energy Pile Considering The Regional Distribution Of Temperature

The large-scale use of traditional petrochemical energy has aggravated the air pollution,and the voice of new energy utilization and development is rising in recent days.As a new method to utilize the shallow geothermal energy,energy piles have dual functions of heat transfer and load-carrying.However,the multi-field coupling makes the thermo-mechanical performance of the pile complex and changeable,and the utilization efficiency of the energy pile is closely related to the temperature regional characteristics.The key to the popularization and development of energy piles is that how to reasonably design the energy piles considering the design functional requirement and local temperature characteristics.In this paper,the thermo-mechanical behavior of energy piles suitable for different temperature regions was studied according to the influence of regional temperature change and the design functional requirements.Firstly,a model test system of energy pile was designed and built based on the similarity principle and FBG sensing technologies.Secondly,the temperature characteristics were summarized and classified considering the relevant codes and the characteristics of energy piles.Then,the thermo-mechanical performance of energy piles in different temperature was studied by the model test method in view of the shortcomings of current energy piles research.And then,the second development was carried out in the finite element software based on the existing boundary surface model,and the numerical simulation was carried out with the experimental prototype,which verified the feasibility and applicability of the numerical method.Finally,the long-term thermo-mechanical behavior of energy piles was investigated by numerical simulation based on the field test.The model test results showed that thermal accumulation effect in soil temperature field was caused by multiple thermal cycles.The thermal stress of increased firstly and then decreased along the pile body and the value of thermal stress increased with the number of thermal cycles.Irreversible settlement of pile head occurred subjected to the thermal cycles,and the irreversible displacement would accumulate with the increase of cycling number but at a lower rate.The experimental results were compared with that of numerical simulation using the boundary surface model,which verified the feasibility and applicability of the numerical method and can be used to study and analyze the thermo-mechanical performance of energy piles.Long-term numerical experiments of thermodynamic characteristics based on field tests showed that for the heating or cooling-dominated temperature regions,the maximum value of thermal axial force induced by thermal cycles during the same time was larger than that in the temperature regions where refrigeration and heating demand was comparable,respectively.In different temperature regions,cumulative displacements occur at the top of the pile,and the cumulative rate decreases with increasing number of cycles.