# A Study on the Softening Shear Model of the Energy Pile-Soil Contact Surface
## 3 Results
### The Evolution of Axial Strain in Pile  
Positive values of the measured temperature strains indicate that the pile has expanded in the axial direction after being heated, and it can be seen from Figure 10 that the temperature strains induced by the pile body upstream of the seepage flow are smaller than those downstream, and the bottom of the energy pile does not undergo any temperature change due to the lack of temperature change. Figure 11 shows the horizontal section of axial additional temperature strain at different operating times and depths of energy piles under simulated working conditions. With the operation of energy pile, the maximum strain at the buried depth of 1.5 m increases from 159.94 to 183.18 \(\upmu\varepsilon\), with a change rate of 14.53%. The maximum strain at 15.5 m increases from 153.35 to 185.45 \(\upmu\varepsilon\), with a change rate of 20.93%. The maximum strain at 22.5 m increases from 150.32 to 183.61 \(\upmu\varepsilon\), with a change rate of 22.14%. The maximum strain at 29.5 m increases from 144.86 to 181.37 \(\upmu\varepsilon\), with a change rate of 25.20%. The maximum strain at 36.5 m increases from 138.72 to 177.97 \(\upmu\varepsilon\), with a change rate of 28.29%. The rate of change of axial additional temperature strain of the pile body gradually increases with the increase in burial depth. Figure 12 shows the distribution of the additional axial temperature strain of the pile body under seepage and non-seepage. As can be seen from Figure 12, the axial temperature strain of the specific point of the energy pile under seepage and non-seepage both increase gradually with operation time. In the operation process from 1 d to 28 d, when the seepage velocity of the fourth layer (fine sand layer) is 49.6 m/a, the maximum value of the upstream temperature strain increases from 114.70 to 160.88 \(\upmu\varepsilon\), which is 40.26%, and the maximum value of the downstream temperature strain increases from 114.72 to 166.65 \(\upmu\varepsilon\), which is 45.26%. The upstream maximum value increases from 115.09 to 165.08 \(\upmu\varepsilon\), which is 43.43% higher under the non-seepage effect when the seepage velocity is 0 in layer 4. The downstream maximum increases from 114.71 to 164.66 \(\upmu\varepsilon\), and is elevated by 43.54%. When the seepage velocity of the five-layer fine sand layer is 48.8 m/a, the upstream temperature strain maximum increases from 111.64 to 150.74 \(\upmu\varepsilon\), being elevated by 35.02%, and the downstream temperature strain maximum increases from 113.54 to 162.99 \(\upmu\varepsilon\), being elevated by 43.55%. Under the non-seepage effect, i.e., when the seepage velocity is 0 in layer 5, the upstream maximum value increases from 112.16 to 158.83 \(\upmu\varepsilon\), being elevated by 41.61%, and the downstream maximum value increases from 113.43 to 159.50 \(\upmu\varepsilon\), being elevated by 40.61%. Figure 10: Upstream and downstream temperature in pile. From the above results, it can be seen that the groundwater seepage can reduce the additional temperature strain of the upstream pile body while increasing the magnitude of the temperature strain of the downstream pile body. This is because seepage will bring the heat from the upstream pile body to the downstream, which makes the temperature of the downstream pile body higher than that of the upstream, and the additional temperature strain of the pile body being positively correlated with the temperature. Figure 13 shows the axial additional temperature strain on the outside of the energy pile body (run continuously for 30 d). It can be seen from the figure that there is an obvious fault in the temperature strain at the junction of strata layers, which is because the elastic modulus and thermal expansion coefficient of different strata are different, resulting in  
Figure 11: Horizontal section of axial additional temperature strain. Figure 12: Cloud diagram of axial additional temperature strain distribution. different temperature strains due to different constraints.