###### Abstract
[18] conducted cyclic thermal response tests on energy piles and found that the heating/cooling process can induce reversible rise/settle of the pile top when the pile top load is less than 30% of the ultimate bearing capacity, respectively. [PERSON] et al. [19] found that the constraint of the superstructure on the pile top significantly affected the distribution of axial stress and the temperature-induced radial deformation of the energy pile, as well as the lateral friction resistance and the bearing performance of the pile foundation. There are some limitations in the in situ experiment and analytical method, and the reliable numerical model has excellent versatility in the study of the energy pile [20]. Compared with other numerical methods, the finite element method can efficiently characterize transient effects; this ensures the specified engineering precision and can deal with complex conditions (such as different types of materials) [20]. Therefore, increasing attention has been paid to the study of the thermomechanical behavior of energy piles using the finite element method. [PERSON] et al. [21] combined the finite element model with the heat transfer theory, analyzed the heat transfer mechanism and heat conduction characteristics of energy piles, and subsequently studied the influence of different media on the thermal conductivity of energy piles. [PERSON] et al. [20] analyzed the mechanical performance of energy pile under the influence of different soil strength parameters; the results show that the axial elongation and contraction of energy pile under the constraint condition is unfavorable to the stability of pile foundation. [PERSON] et al. [22] investigated the temperature-induced stress and found that the dynamic lateral friction (induced by temperature) has little effect on the bearing capacity of end-bearing piles. [PERSON] et al. [23] investigated the reasons for the increase in bearing performance with temperature growth and found that the contact pressure between pile and soil is generally smaller than 15 kPa. The unsteady-state temperature distribution of energy piles is the basis for the study of both thermomechanical behavior and heat transfer performance of energy piles [4; 24; 25]. This is because the generation of thermal stress during the heat transfer process may have a significant effect on the stress distribution of the pile foundation structure [1; 22]. However, the temperature field around energy piles is less studied under typical intermittent operation and unbalanced thermal load conditions. There are few reports on the thermal behavior of the energy pile group, especially the influence of different arrangement modes on the thermal performance of the energy pile group. This is because each pile in the group is connected together through the platform, the load acting upon the pile is borne by both the pile and the foundation, and the load transfer mechanism of the pile group is different from that of a single pile and is more complex [26]. In this paper, a finite element numerical model was proposed and verified in order to identify the temperature field distribution around the energy pile and the thermomechanical behavior of the group. First, the heat conservation control differential and thermomechanical equation of energy pile were proposed, and a finite element numerical model, which enables the evaluation of the temperature field of energy pile and the thermomechanical behavior of the pile group, was developed. A full-scale in situ test of a large diameter over-length energy pile (1000 mm-diameter, 44 m-long) was carried out to verify the model. Second, the distribution of temperature field in pile body and surrounding underground under typical intermittent working conditions (heating load and cooling load unbalance conditions) were determined. The conceptual model of thermal load under typical intermittent operation conditions was proposed. Thermomechanical behavior characteristics of the energy pile group were determined, and the influences of arrangement on it were analyzed.