## 2 Overview of the DBP-EP Model Test  
### DBP-EP and Soil Condition  
The experimental location for this study is situated at the snow and ice melting test base of Hubei University of Technology in Wuhan, China, as illustrated in Figure 2. The dimensions of the model tank measure 1200 mm \(\times\) 1200 mm \(\times\) 1200 mm, with its internal surface insulated using 50 mm thick extrusion board. The test pile consists of a prefabricated model measuring 1000 mm in length, maintaining a scaling ratio of 1:25 between the pile and the heat exchanger pipe. The materials used for the mold of the pile body comprise a PVC plastic pipe with an inner diameter of 0.1 mm and a steel pipe with an inner diameter of 30 mm, along with a 3D-printed base and an accompanying 3D-printed components to secure the upper steel pipe centered within the setup. When assembled, the PVC exterior needs to be reinforced with wire, and after the assembly is completed, cement mortar is poured into the mold, and the ratio of cement mortar is water-sand-cement = 0.23:1.1:0.3. The pipe embedded within the pile is made of copper, featuring an outer diameter of 6 mm, an inner diameter of 4.8 mm, and a total length of 8000 mm. Given that the DBP-EP in situ testing focuses solely on the thermal response of the heat exchanger tubes that extend from the pile's body, these tubes are positioned horizontally during this test to maintain a consistent length for the circulating liquid heat exchanger pathway. The constant load at the top of the pile was applied by weights, with a single weight of 100 N. A separate 3D-printed model was fabricated as the base of the loading plate, and space was reserved at the bottom of the model for the heat exchanger tubes and the sensor lines. The top loading plate is an aluminum square plate with a weight of 66 N. The weights and micrometer are placed on top of the plate. The pile was placed in the center of the model tank; the layout of the measurement points inside the pile and the soil conditions around the pile are shown in Figure 3. One group of temperature probes, T\({}_{A}\), was embedded in the pile, and six groups of temperature probes, T\({}_{B}\), T\({}_{C}\), T\({}_{D}\), T\({}_{E}\), T\({}_{F}\) and T\({}_{G}\), were embedded around the pile. The T\({}_{A}\) group of temperature probes was fixed on the side surface of the steel pipe before pouring the pile, and the probes were poured into the pile, along with the steel pipe. In the T\({}_{B}\) group, the temperature probes were affixed to the lateral surface of the pile body, allowing for direct measurement of temperature variations from that specific location. In contrast, the temperature probes utilized in the T\({}_{C}\), T\({}_{E}\), T\({}_{F}\), and T\({}_{G}\) groups were secured to steel reinforcement bars and embedded within the soil body. This setup facilitates comprehensive temperature monitoring throughout the surrounding environment of the pile. Furthermore, four temperature sensors were arranged at the upper and lower parts of the energy pile, specifically located at the entrance and exit of the heat exchange tube. These probes play a crucial role in tracking the temperature fluctuations of the circulating water within the heat exchange system, ensuring that the inlet water maintains a consistent temperature. Figure 2: Field diagram of indoor modeling test. Furthermore, the earth pressure monitoring system incorporates two pressure cells, with a diameter of 28 mm and a thickness of 10 mm. The pressure cells are embedded in layers on the bottom of the pile during the sand filling process. The temperature probes at T\({}_{\rm A}\), T\({}_{\rm B}\), T\({}_{\rm C}\), T\({}_{\rm D}\), T\({}_{\rm E}\), T\({}_{\rm F}\), and T\({}_{\rm G}\) were placed from 50 mm below the surface of the earth, and the spacing between each of the temperature probes along the depth direction was 200 mm.