Study On Analysis Method For Mechanical Behaviors Of Energy Pile Groups

The energy pile is a new type of pile which combines the ground source heat pump technology with the conventional pile foundation,and plays the role of bearing the superstructure load and heat exchange with the foundation.Under the effect of temperature-mechanical coupling,the working performance of the energy pile group foundation is different from that of the conventional pile group.Therefore,it is important to study the practical analysis method which can reasonably consider the interaction of pile group.In this paper,based on the previous work and considering the influence of temperature and the interaction of pile groups,the governing equations of the mechanical properties of pile groups under the thermal-mechanical coupling are derived.The main research contents and conclusions of this paper are as follows:(1)A method based on the analysis method of working performance of the conventional single pile is proposed for the working performance analysis of single energy piles,in which the unloading and reloading characteristics of pile-soil interface are simulated by Pyke criterion.The proposed method is validated by comparing the predicted values with the data collected from literatures.(2)A method based on the analysis method of working performance of the single energy pile is proposed for the working performance analysis of energy pile groups,in which the transfer of shear stress on the side of pile and stress at pile tip in the foundation is considered to reflect the interaction between two piles.The proposed method is validated by comparing the predicted values with the data collected from literatures,and the design chart of the interaction coefficient of the energy pile is given.(3)The mechanical characteristics of the energy pile group are analyzed by the proposed method.The computed results indicate that:Under the pure temperature load,the displacement direction of single pile is the same as that of pile group.Due to the interaction of pile groups,the displacement of pile groups is larger than that of single pile with the same temperature increment,and the displacement ratio of pile groups and single pile decreases with the increase of temperature increment.The interaction of pile groups caused by mechanical load is greater than that caused by temperature load under thermal-mechanical coupling.Under load-heating coupling,the pile top of pile group foundation may sink,which is different from the uplift of pile top of single pile,indicating that the interaction of pile groups must be considered in the design of energy pile foundations.