# Study on the Effect of Insulation Materials on the Temperature Field of Piles in Ice-Rich Areas
## 4 The Effect of Insulation on the Temperature Field of Pile Foundation
### Effect of Insulation Thickness on the Temperature Field of Pile Foundation
Increasing the thickness of the insulation layer was significantly less efficient than increasing the temperature of the pile foundation when the thickness was greater than 10 cm. This is because the heat of hydration of the pile concrete is fixed, and upon increasing the thickness of the insulation layer, the concrete's heat of hydration loss is reduced. Thus, when the insulation layer reaches a certain thickness, it can retain most of the heat of hydration, so continuing to increase the thickness of the insulation layer reduces the amount of heat retained, so the pile body temperature increase is reduced. In real projects, we have to consider saving insulation material and reducing the construction period. Combined with the concrete ratio used in the project, we chose an insulation layer thickness of 10 cm to achieve the best effect. Effect of the Thermal Conductivity of Insulation Material on the Temperature Field of Pile Foundation  
The basic parameters of insulation materials are density, specific heat capacity, and thermal conductivity. The density and specific heat capacity of an insulation material account for less than 1% of the effect on the temperature of the pile. Thermal conductivity has a great influence on temperature. For this reason, we chose to analyze the thermal conductivity of the insulation. To study the effect of the thermal conductivity of the insulation material on the temperature of the pile, we took the most suitable insulation thickness of 10 cm from the finite element simulation and set its material thermal conductivity to 0.02 W/M\(\cdot\)K, 0.045 W/m\(\cdot\)K, 0.07 W/m\(\cdot\)K, 0.095 W/m\(\cdot\)K, 0.12 W/m\(\cdot\)K, respectively. We took the temperature data of 7 d and 28 d for analysis. Figure 10 shows that the pile body temperature gradually decreased upon increasing the thermal conductivity of the insulation material around the pile. At 7 d, the material insulation coefficients of 0.02 W/m\(\cdot\)k, 0.045 W/m\(\cdot\)k, 0.07 W/m\(\cdot\)k, 0.095 W/m\(\cdot\)k, and 0.12 W/m\(\cdot\)k for pile temperatures of 15.5 \({}^{\circ}\)C, 13.7 \({}^{\circ}\)C, 12.2 \({}^{\circ}\)C, 11.1 \({}^{\circ}\)C, and 9.5 \({}^{\circ}\)C, respectively. At 28 d, the pile temperatures were 0.73 \({}^{\circ}\)C, 0.16 \({}^{\circ}\)C, \(-\)0.14 \({}^{\circ}\)C, \(-\)0.35 \({}^{\circ}\)C, and \(-\)0.57 \({}^{\circ}\)C. The use of materials with lower insulation coefficients has a significant effect on raising the temperature of the pile. Figure 11 shows that as the thermal conductivity of the insulation increased, the maximum pile temperature decreased. At a lower thermal conductivity, the pile more quickly reached 0 \({}^{\circ}\)C refroze. This occurred because the greater the thermal conductivity of the insulation material, the faster the heat flow through the insulation and the faster the heat loss from concrete hydration under the concrete and permafrost temperature gradient. This decreased the pile-side temperature with increasing thermal conductivity at the same insulation thickness. Figure 9: Temperature change of pile foundation at 7.4 m.  
Figure 12 shows that changes in the thermal conductivity of the insulation material were roughly linear with changes in the pile body temperature. The maximum temperature of the pile base was still located away from the temperature that would damage the later strength of the concrete. This means that when the insulation layer was 10 cm, insulation material with a lower thermal conductivity could be used to ensure that the pile body concrete meets the adiabatic temperature rise rate and maximum maintenance temperature. The thermal conductivity of the insulation layer was reduced, allowing it to better retain the heat of hydration and also prevent ambient temperature loss. Thus, the temperature gradient was lower, and the rate of loss of hydration heat to the outside was reduced. This allowed the concrete's temperature to be maintained and also reduced the radius of disturbance during the construction of bored piles.