Study On Load Transfer Characteristics Of Geothermal Energy Piles Under The Coupling Of Construction Load And Temperature

The static drill rooted geothermal energy piles is a new type of geothermal energy pile combining static drilling root planting method and ground source heat pump technology.It buries the heat exchange tube in the cement soil on the side of the pile,which not only facilitates construction,but also improves the heat exchange efficiency,has broad engineering application prospects.As a new type of building energy-saving technology,geothermal energy piles have been applied in many buildings at home and abroad,but has not yet formed a complete set of design regulations.At present,the research and application of geothermal energy piles in deep soft ground are few.Due to the limitation of test cost and site,there are not many on-site measurements,especially the lack of long-term thermo-mechanical characteristics research,so it is difficult to evaluate the safety and durability of geothermal energy pile structure.In this paper,field tests combined with numerical simulation are used to study the heat transfer and bearing performance of geothermal energy piles under different working conditions and long-term temperature load.The article provides suggestions for the engineering design and construction of geothermal energy piles,and provides a basis for the further promotion and application of geothermal energy piles.1.In terms of the heat transfer performance of geothermal energy piles,this paper tests the thermal conductivity of the rock and soil body through the thermal response test.According to the temperature change law of pile body and soil body during the operation of geothermal energy pile,the heat transfer law of pile body and soil body is analyzed.Finally,a numerical model is established to analyze the heat transfer efficiency of geothermal energy piles with different heat exchange distances and different thermally conductive materials.Through the temperature change of the pile body and the soil during the field test of the geothermal energy pile summer mode,the temperature change law of the pile and the soil during different test periods can be obtained.The results show that the initial average temperature of the soil is affected by the atmospheric temperature and there is a slight difference between the top and bottom of the pile.During the test,the temperature distribution of the pile body is greatly affected by the heat dissipation conditions at both ends of the pile and the thermal conductivity of the soil around the pile.The sudden temperature rise of the soil at twice the pile diameter relative to the pile is not an instantaneous response,but a large delay.The temperature influence radius of this test pile is between 2 times the pile diameter and 4 times the pile diameter.After the pile body is naturally heated for 19 days,the average temperature of the soil at the 2 times pile diameter range has increased by 1 ° C.It shows that the heat dissipation during recovery period is quite slow.Through the thermal response test,the average initial temperature and the integrated thermal conductivity of the on-site soil can be calculated,and a three-dimensional heat transfer numerical model can be established to analyze the heat transfer efficiency of geothermal energy piles with different heat exchange distances and different heat conductive materials.The results show that increasing the heat transfer tube spacing,heat transfer tube heat transfer coefficient,and the thermal conductivity of the cement soil around the pile can improve the heat transfer efficiency of the geothermal energy pile.2.In terms of the thermo-mechanical structural response of geothermal energy piles,the internal force changes of the pile body of the geothermal energy pile and the load transfer relationship with the soil around the pile are carried out under the combined action of the superstructure load and the temperature load of different working conditions.Through the field test of the geothermal energy pile in summer mode(pile heating)and winter mode(pile cooling),the variation law of the pile body axial force and the lateral friction resistance of the geothermal energy pile under the combined action of building load and temperature load are analyzed.Besides,comparing the field tests of other geothermal energy piles at home and abroad,the influence of pile top constraints and the properties of the soil layer around the pile on the thermo-mechanical properties of geothermal energy piles are analyzed.The research results show that during the actual operation of geothermal energy piles,the additional stress of the pile body caused by temperature load and the changes in the friction resistance of the pile side are closely related to the constraint of the pile top.The distribution of the soil layer around the pile and the nature of the soil layer will also affect the pile body.The distribution of stress and frictional resistance on the side of the pile has an impact.Therefore,when analyzing the bearing performance of geothermal energy piles,the basic physical and mechanical parameters and thermal physical parameters of the soil layer around the pile,cyclic temperature loads and pile top constraints should be considered in order to better guide the design of geothermal energy piles and construction.This paper discusses the heat transfer performance and structural thermo-mechanical response of geothermal energy piles around heat transfer and structure.It uses field tests and numerical simulations to analyze and compare the heat transfer performance and structural thermo-mechanical response of geothermal energy piles.Discussing the stress characteristics and possible problems of geothermal energy piles as a buried pipe carrier of ground source heat pump systems,and provides a basis for the further promotion of geothermal energy piles.