Study On Load Transfer Mechanism Of Single Energy Piles Under Thermo-mechanical Loading

The energy pile is a new pile foundation that combines the ground source heat pump system with the traditional pile foundation,which has the function of bearing and heat transfer,and has a good application prospect.However,there are few researches about the load transfer mechanism of the single energy pile under thermal coupling,which restricts the popularization and application of energy piles.In this paper,the load transfer mechanism of single energy pile is studied through model slot test,theoretical analysis and numerical simulation.The main works and conclusions are as follows:(1)The model slot test is used to analyze the effect of temperature on the working characteristics of the energy pile under different pile top load and soil conditions.The results show that:The pile strain and the pile tip compressive stress will increase with the increase of temperature and decrease with the decrease of temperature.After the temperature recovers,the pile strain and pile tip compressive stress with top load cannot restore to the initial value;The sinking of the pile caused by cooling is greater than the rising deformation when the temperature rises,and there is residual settlement at the top of the pile.(2)A simplified calculation method for the energy pile under the thermo-mechanical coupling effect is established based on the single-pile load transfer method,the pile-soil load transfer function chooses a hyperbolic model,and the Masing rule is used to simulate the unloading characteristic of the pile-soil interface.The simplified method is verifyied the rationality and reliability through engineering examples,the results show that the simplified method can simulate the working characteristics of single energy pile under thermal coupling.(3)The parametric sensitivity analysis is performed on single energy pile with the proposed simplified method,and the performance characteristics of energy pile under different pile lengths,pile top loads,temperature increaase,soil at the pile tip and pile top constraints are compared.The results show:the maximum pile temperature stress of the pile body will increase with the increase of pile length,temperature increase,soil stiffness at the pile tip and the constraint of the pile top,but it will decrease with the increase of pile top load;As the pile length becomes larger and the soil stiffness at the end of the pile increases,the point of maximum temperature stress will move down the pile,when the pile top load,temperature increase and the constraint of the pile top become larger,the point of maximum temperature stress will move up the pile.