Experimental Study And Numerical Simulation Of Thermodynamic Properties Of Phase-Change Piles In Saturated Sand

Energy pile is a new type of pile foundation in recent years.It combines the heat exchange tube with the ordinary pile body to achieve the purpose of using the geothermal energy to meet the building’s own heating and cooling demand balance.Compared with the traditional pile foundation,the energy pile needs to bear the function of supplying energy to the building in addition to the upper load,connecting the building and supporting the soil.Therefore,the analysis of the mechanical properties of energy piles is particularly important.Based on the similarity principle,this paper systematically analyzes the mechanical properties of energy piles through large-scale model tests,and numerically simulates the model tests using finite element software.The main work content and research results are as follows:(1)This paper summarizes the methods and methods of energy pile research at home and abroad,and discusses the existing problems of energy pile technology.(2)The heat transfer of heat exchange tubes and energy piles,the heat transfer inside the piles,and the heat exchange theory between the energy piles and the surrounding soils are elaborated and analyzed.(3)A model test was carried out to embed a large-scale precast concrete pile with a diameter of 0.2 m and a length of 1.5 m into a steel box with saturated sand.The size of the steel box was 2.45 m × 2.45 m × 2 m(length × width × height),the mechanical properties of the energy pile under long-term cyclic temperature load are studied.The results show that:(1)The energy pile will bring a certain temperature accumulation under the cyclic temperature load;(2)Uneven stress and strain distribution along the depth direction of the pile and the same plane inside the pile;(3)The displacement of the pile will occur during the temperature cycle,and an unrecoverable plastic displacement will occur after the end of the temperature cycle.(4)Under the cyclic temperature load,the energy pile will not only produce the mechanical properties of the pile,but also affect the soil pressure and pore pressure change of the soil around the pile.(4)The ABAQUS finite element analysis software was used to model the energy pile model test,and the correctness of the model test results was verified.The results show that the numerical simulation results are in good agreement with the test results.The mechanical properties of ordinary piles and phase-change piles under temperature load were analyzed by using the validated model.The mechanical properties of energy piles under different temperature gradient conditions were analyzed.The results show that(1)phase change materials can reduce the thermal response of the energy pile under temperature load to a certain extent.Under the same temperature load condition,the phase change pile has a certain reduced temperature,stress,expansion amount and pressure change around the pile.(2)Although the higher temperature gradient can increase the heat exchange capacity of the energy pile,it will also increase the heat load of the energy pile,which will cause more changes in the mechanical properties of the energy pile.