# A Study on the Softening Shear Model of the Energy Pile-Soil Contact Surface
## 3 Results
### The Evolution of Temperature in Pile and Surrounding Soil  
After the energy piles were operated for 28 d, the measured temperature values upstream of the seepage under the in situ test condition were 32.25, 34.81, 31.18, 29.43, 30.31, 19.68 and 19.75 \({}^{\circ}\)C in order from shallow to deep, and the measured temperature values downstream of the seepage were 36.00, 33.56, 35.02, 31.97, 34.81, 19.81 and 19.75 \({}^{\circ}\)C. The temperature change rates upstream and downstream of the seepage were 12%, -4%, 12%, 9%, 15%, 1% and 0% in order from shallow to deep. Under the numerical simulation condition, the temperature probe was used to extract the temperature values of the pile body, and the measured temperature values upstream of the seepage were 35.16, 34.72, 34.58, 31.30, 30.61, 20.00 and 20.00 \({}^{\circ}\)C from the shallow layer to the deep layer, and the measured temperature values downstream of the seepage were 35.87, 35.32, 35.07, 34.24, 33.45, 20.00 and 20.00 \({}^{\circ}\)C from the shallow layer to the deep layer, respectively. The temperature change rates upstream and downstream of the seepage under simulated conditions were 2%, 2%, 1%, 9%, 9%, 9%, 0% and 0% in order from shallow to deep. A comparison of the temperature change rates shows that the temperature values on the  
Figure 8: Temperature additional pressure on pile side. upstream side of the pile under seepage are usually smaller than those on the downstream side, and the temperature change rate with time in the seepage stratum is larger than that in the non-seepage stratum, which is consistent with the conclusion that seepage can enhance the heat transfer performance of energy piles. The temperature change curves with time at different locations from the heat exchanger pipe in the seepage layer are shown in Figure 9, and there is an obvious difference between the upstream and downstream temperature trends of the soil around the pile as the energy pile runs with seepage. It can be seen from Figure 9, when there is no groundwater seepage, that the temperature field of the soil body around the pile is symmetrically distributed with the energy pile as the center, and the temperature of the soil body around the pile gradually increases with the increase in the running time of the energy pile, and the range of thermal influence increases. After 30 d of continuous operation, the thermal influence range of both upstream and downstream is 2.1 m. When the seepage rate is 50 m/a, the upstream thermal influence range is 1.1 m, which is a reduction of 47.61% compared to no seepage, and the downstream thermal influence range is 3.4 m, which is an increase of 61.90% compared to no seepage. When the seepage rate is 100 m/a, the upstream thermal influence range is 0.7 m, which is a reduction of 66.66% compared to no seepage, and the downstream thermal influence range is 4.6 m, which is an increase of 119.04% compared to no seepage. It can be seen from the above results that when there is seepage, the heat accumulation area downstream of the energy pile is not fixed. Specifically, as the seepage velocity increases, the heat accumulation area decreases, because the larger seepage velocity takes away more heat. Moreover, with the increase of the operation time, it keeps moving downward to the seepage direction, and the heat influence range perpendicular to the seepage direction keeps decreasing, so the seepage can dissipate heat from the upstream soil region and effectively reduce the heat accumulation problem of the upstream soil. Figure 10 shows the temperature change curve of the outer side of the pile body of the upstream and downstream energy piles with depth during 30 d of continuous operation. From the curve in Figure 10, it can be seen that with the increase in burial depth, the temperature value of the pile-soil interface first rises rapidly and then decreases in segments. The temperature first rises because the ground temperature of the shallow layer is affected by the outside air. Moreover, the temperature change amplitude is relatively small.