Model tests on temperature field and heat exchange efficiency of energy pile in loess foundation
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摘要: 为研究黄土地基中能量桩热交换效率特性，开展了夏季/冬季模式下不同饱和度黄土中能量桩模型试验。试验采用了饱和度分别为42%、69%的重塑黄土，模型桩为钢筋混凝土预制桩，内置了U型、W型2种换热管，桩径采用了50、65、80 mm三种规格，利用埋入/静力压入2种方式将能量桩设置在黄土中。试验结果表明：桩土温度场表现出明显的三维特征，桩土热量交换以水平方向为主，能量桩温度水平影响范围不小于3倍桩径；桩侧土温度梯度与黄土饱和度、运行模式、施工挤土效应及换热管型式密切相关；整体上，夏季模式下能量桩热交换效率低于冬季模式，夏季模式下黄土饱和度较高时热交换效率也较高，而冬季模式下相反；不论冬季模式还是夏季模式，黄土饱和度相同时，W型换热管埋入桩热交换效率高于U型换热管静压桩，U型换热管埋入桩的热交换效率最低，桩径为50、65 mm能量桩的热交换效率基本相当，而桩径为80 mm能量桩的热交换效率显著降低；与非挤土桩相比，挤土桩能平均提高热交换效率约13.7%。Abstract: Model tests on energy piles in loess with different saturation degrees under summer/winter mode were conducted to understand the heat exchange efficiency characteristics. Remolded loess was used with saturation degrees of 42% and 69%, respectively. The precast reinforced concrete piles were applied as the model energy pile, with diameters of 50, 65, and 80 mm, installed with U-shaped and W-shaped heat exchangers. The energy piles were placed in the loess using two methods: embedded/static jacking. The experimental results show that the temperature field in surrounding soils exhibits obvious three-dimensional characteristics, and the heat exchange between the pile and soil is mainly in the horizontal direction. The horizontal influence zone of the energy pile temperature is not less than 3 times the pile diameter. The temperature gradient in surrounding soils is closely related to the saturation degree of loess, operating mode, soil displacement effect during construction, and heat exchanger type. Overall, the heat exchange efficiency in summer mode is lower than that in winter mode. A higher saturation degree for loess corresponds to a higher heat exchange efficiency in summer mode, while the truth is the opposite in winter mode. Either in the winter or summer mode, when the loess saturation degree is the same, the heat exchange efficiency of embedded piles with W-shaped heat exchanger in loess is higher than that of jacked piles with U-shaped heat exchanger, while the heat exchange efficiency of embedded piles with U-shaped heat exchanger is the lowest. The heat exchange efficiency of energy piles with diameters of 50 and 65 mm is nearly the same, while that of 80 mm diameter ones is much lower. Compared with non-displacement piles, the displacement piles can improve the heat exchange efficiency by around 13.7% averagely.
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Key words:
- subgrade engineering /
- energy pile /
- model test /
- temperature field /
- heat exchange efficiency /
- loess foundation
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图 3 直径50 mm能量桩夏季模式下的稳态温度场
Figure 3. Steady temperature field of energy piles in summer operation mode (D=50 mm)
图 4 直径50 mm能量桩冬季模式下的稳态温度场
Figure 4. Steady temperature field of energy piles in winter operation mode (D=50 mm)
图 5 直径65 mm能量桩夏季模式下的稳态温度场
Figure 5. Steady temperature field of energy piles in summer operation mode (D=65 mm)
图 6 直径65 mm能量桩冬季模式下的稳态温度场
Figure 6. Steady temperature field of energy piles in winter operation mode (D=65 mm)
图 7 直径80 mm能量桩夏季模式下的稳态温度场
Figure 7. Steady temperature field of energy piles in summer operation mode (D=80 mm)
图 8 直径80 mm能量桩冬季模式下的稳态温度场
Figure 8. Steady temperature field of energy piles in winter operation mode (D=80 mm)
图 9 黄土地基饱和度对能量桩热交换效率的影响
Figure 9. Effect of loess foundation saturation degree on heat exchange efficiency of energy piles
图 10 换热管型式对能量桩热交换效率的影响
Figure 10. Effect of heat exchanger type on heat exchange efficiency of energy piles
图 11 桩径对能量桩热交换效率的影响
Figure 11. Effect of pile diameter on heat exchange efficiency of energy piles
图 12 能量桩施工方法对热交换效率的影响
Figure 12. Effect of energy pile construction method on heat exchange efficiency
表 1 黄土物理力学性质
Table 1. Physical and mechanical properties of loess
土类型 含水量/% 密度/(g·cm-3) 孔隙比 土粒相对体积质量 饱和度/% 导热系数/(W·m-1·K-1) 比热容/(kJ·m-3·K-1) 原状黄土 15.4 1.56 0.98 2.67 42 0.68 2 151 重塑黄土① 15.2 1.58 0.95 42 0.68 2 177 重塑黄土② 23.8 1.72 0.92 69 1.08 2 460 
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表 2 模型试验方案
Table 2. Model test schemes
试验编号 桩径/mm 换热管型 土体饱和度/% 桩入土方式 ① 50 U型 42 埋入 ② 50 U型 42 静压 ③ 50 U型 69 埋入 ④ 50 U型 69 静压 ⑤ 50 W型 42 埋入 ⑥ 50 W型 69 埋入 ⑦ 65 U型 42 埋入 ⑧ 65 U型 42 静压 ⑨ 65 U型 69 埋入 ⑩ 65 U型 69 静压 ⑪ 65 W型 42 埋入 ⑫ 65 W型 69 埋入 ⑬ 80 U型 42 埋入 ⑭ 80 U型 42 静压 ⑮ 80 U型 69 埋入 ⑯ 80 U型 69 静压 ⑰ 80 W型 42 埋入 ⑱ 80 W型 69 埋入
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