## 1 Introduction  
In recent years, energy piles have gained prominence in engineering as an innovative technology derived from ground source heat pumps [1; 2; 3]. These piles have the dual functions of bearing loads and transferring heat. In addition to supporting the structural load of upper buildings, they also play a crucial role in facilitating heat exchange between piles and the surrounding soil. Energy piles harness geothermal energy and minimize adverse environmental impacts. Nowadays, energy piles are widely used in several developed nations, such as Austria, Germany, and the United Kingdom [4; 5; 6; 7]. Moreover, research focused on energy pile technologies is increasing. [PERSON] et al. [8] conducted an energy pile test on a silty clay foundation and discovered that repeated heating and cooling cycles could lead to a settlement between the pile top and the soil surface. [PERSON] et al. [9] conducted tests on energy piles in saturated clay and observed that repeated thermal cycles caused the irreversible settlement of the piles. [PERSON] et al. [10] analyzed the thermal performance of a large-diameter bored pile on a soft soil foundation. Theyinvestigated how fluid circulation and temperature variations within the formation impact the thermal performance of the energy pile. The thermal-mechanical response of energy piles is not only affected by external thermal and force loads but also depends on the properties of the piles [11; 12; 13]. By adding steel fiber to a pile, the thermal conductivity of the pile can be improved, which will enhance the heat transfer efficiency of the energy pile [14; 15; 16]. On the other hand, the mechanical properties of a pile can be effectively improved. In recent years, many scholars have studied the properties of steel fiber-reinforced concrete piles. [PERSON] [17] studied the effect of steel fiber inclusion on the mechanical properties of steel fiber-reinforced concrete. The results showed that the strength of the specimen increased, and the overall mechanical properties of the steel fiber-reinforced concrete specimen were significantly better than that of a plain concrete specimen, which indicates that steel fiber can effectively improve the toughness of concrete and prevent cracks. To clarify the influence of fiber volume fraction on the thermal properties of cement concrete, [PERSON] et al. [18] studied the thermal conductivity of steel fiber concrete and carbon fiber concrete through experiments and composite theoretical models. The results show that the volume fraction of steel fiber significantly affects the thermal properties of concrete, and steel fiber forms a network structure that effectively improves the heat conduction of concrete. Cyclic thermal loading causes significant thermal stress between a pile and the soil, resulting in the irreversible settlement of the pile. Introducing phase change material (PCM) into energy piles can help mitigate the impact of thermal loading [19; 20]. PCM can maintain a constant temperature and supply latent heat through changes in its state [21; 22; 23]. PCM possesses the characteristics of high energy density and minimal temperature fluctuations; this is why PCM has been incorporated into pile systems [24; 25; 26]. By incorporating expanded graphite and a nanoscale composite PCM, [PERSON] et al. [27] developed an integrated cement-based composite material suitable for energy piles. They subsequently conducted experimental tests to assess its mechanical properties. The results indicated an increase in the bending strength of the cement-based composite materials with an increase in the content of composite PCM. [PERSON] et al. [28] introduced an expanded graphite base and a graphite nano matrix composite PCM to an energy pile. The results showed that the strength of the energy pile, which was incorporated with 10% composite PCM, reached 37 MPa. [PERSON] et al. [29] enhanced energy piles by incorporating PCM into the concrete within a pile.