基于实测的桩基埋管换热性能和温变沉降特征分析

In-situ test analysis of the heat transfer features of the energy piles and their settlement due to cyclic temperature variations

通过对江苏某实际工程传统钻孔单U和并联双U埋管、桩基并联双U及并联双螺旋埋管换热器进、出口水温、流速的实测,以单位井深换热量为性能指标,结合经济性指标E,对比分析了4埋管换热器换热性能和经济性的差别。分析了桩基埋管换热器运行过程中冷、热堆积对其换热性能的影响。进一步对桩基埋管换热器进行了温度-荷载联合测试,模拟冬、夏两季能源桩承载运行的取、放热工况,获得了能量桩的桩身温度分布和桩顶动态沉降曲线,分析了桩顶换热过程中因热胀冷缩而产生位移的规律性,指出桩顶沉降累积量过大会导致桩基失稳,这一点在能量桩的设计阶段应注意加以考虑。

The paper is to engage in an in-situ test analysis for the heat transfer features of energy piles and their settlement due to the cyclic temperature variations based on the data we have gained in the said tests. Practically speaking,we have done the tests in a certain practical project in Jiangsu and analyzed the results concerned by using an index of the heat transfer per unit borehole depth and economic index E,including the borehole heat exchanger（ BHE） with a single U-tube,BHE with a parallel double U-tube and the pile foundation（ PF） along with a parallel double U-tube and PF with a parallel double Helix-tube. For the research purpose,we have measured and recorded the water temperature at the inlet and the outlet of the underground heat exchanger and the water flowing rate through the U-tubes in each BHE and PF. In addition,we have also analyzed the impact of the cold and heat accumulation situation on the heat transfer performance of the energy piles. What is more,an external force has also to be exerted to the two energy source piles in the different geometries while they were being heated or cooled due to the temperature variations caused by the rejection of heat in summer and absorption in winter on the actual operational conditions needed.At the same time,we have also been keeping monitoring activities in the process of the temperature changes of the structure and displacements of the piles＇ top surfaces via the thermal couples and stress sensors. Besides, we have also illustrated the coupled effects of the temperature variations and conventional static loads on the variation modes of the piles top displacements due to the aforementioned heat rejection and natural recovery cycle processes,which help to disclose the settlement features of the two sorts of energy piles caused by the cyclic temperature variations in the test. It is perhaps due to the accumulation of the displacements that may have resulted in the pile instability. Thus,further studies are needed to make clear whether the instability aroused by frequent cyclic temperature variations in a long run is likely to cause damage to the building structures. Besides,this should also be paid close attention to in the design stage of the energy piles.