能量桩通过内置循环管与周围土体进行热交换来开采浅层地热能。通过室内模型试验,测试4个完整的冷热循环过程中能量桩仅受温度作用及热-力耦合两种工况下的桩身和桩侧土体温度、桩顶和桩侧土表面沉降、桩顶荷载及桩身内力,分析黄土地基中埋设单U形换热管的能量桩热力学及承载变形特性。试验结果表明,对于每个冷热循环过程,随循环时间增加能量桩热交换效率逐渐降低并趋于稳定状态,黄土地基中能量桩桩身温度随深度增加逐渐减小。冷热循环会使能量桩桩顶产生累积沉降,与仅受温度作用工况相比,在热-力耦合作用下能量桩桩顶累积沉降较大,桩侧土表面沉降较小,而桩侧土体受影响范围则较大。对于两种工况,冷热循环稳定后能量桩最大附加应力均出现在桩身中部,热循环时桩身上部摩阻力为负,下部摩阻力为正,冷循环时则相反。
Abstract
Energy piles utilize shallow geothermal energy by exchanging heat with surrounding soils through built-in circulating pipe. Model tests were conducted to investigate the behavior of energy pile embedded in loess soils during 4 entire heating-cooling cycles under two conditions, i.e., the energy pile only experienced heating-cooling cycles and the energy pile experienced loading throughout the heating-cooling cycles. The variation of the temperature of the pile and surrounding soils, the settlement of the soil surface and the pile as well as the pile head load and its internal force were recorded. Furthermore, the load-bearing deformation characteristics and thermo-mechanical characteristics of energy pile with single U-shaped heat exchanger were analyzed. The test results indicated that the pile heat transfer efficiency gradually decreases to a stable state with the development of cycling. The temperature in the energy pile shaft in loess soils decreases with the depth and the cooling-heating cycles will cause accumulation of settlement of the pile. Compared with the energy pile only experiencing heating-cooling cycles, the energy pile experiencing loading throughout the heating-cooling cycles will result in a greater accumulative settlement of pile and a smaller settlement in soil surface as well as a greater range of soils influenced surrounding the pile. For the two above conditions, the maximum superimposed stress will occur near the middle of the pile shaft after the cooling-heating cycles are stable. Heating process will induce negative, positive skin friction on the upper and lower pile shaft, respectively. While cooling process will cause opposite skin friction on the upper and lower pile shaft.
关键词
地热能 /
能量桩 /
黄土地基 /
模型试验 /
冷热循环 /
热-力耦合
Key words
geothermal energy /
energy pile /
loess foundation /
model test /
cooling-heating cycles /
thermo-mechanical coupling
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