非对称循环温度荷载下2×2能源群桩倾斜性状离心机试验研究

Centrifuge modelling of inclination of 2×2 energy pile groups subjected to non-symmetrical cyclic thermal loading

在能源桩地源热泵系统运行过程中,能源群桩基础可能产生非对称温度分布,导致基础倾斜,对其正常使用构成不利影响因素。研究通过离心机试验,量化了砂土中2×2能源群桩在非对称循环温度荷载下的倾斜变形,试验在恒定竖向荷载下施加15个幅值为10℃的双向循环温度荷载,共开展10个试验,研究了群桩基础中能源桩非对称布置形式、竖向荷载大小以及筏板-土体相互作用对基础倾斜的影响。结果表明:非对称循环温度荷载导致基础倾斜不断累积并逐渐趋于稳定,在正常竖向荷载作用下(安全系数2.0),基础累积倾斜约1.8‰,小于规范限值2.5‰,群桩发生轴力重分布,最大轴力增加约40%初始值;随着竖向荷载的增加,基础累积倾斜有可能超过2.5‰。非对称循环温度荷载所导致群桩基础倾斜在设计中应予以考虑。

During the operation of energy pile-based ground source heat pump systems,the energy piles may experience non-symmetrical temperature changes,resulting in inclination of pile group.This can affect its serviceability unfavourably.By conducting centrifuge tests,the inclination of 2×2 energy pile groups in sand induced by non-symmetrical cyclic thermal loading is quantified.During each test,15 two-way thermal cycles with an amplitude of 10˚C are applied while maintaining a constant vertical load.A total of 10 tests are carried out to evaluate the effects of the distribution of energy piles within the group,magnitude of vertical load and raft-soil interaction on the inclination of pile groups.The results show that the inclination of pile group accumulates with thermal cycles at a reducing rate.Under normal vertical load(FoS=2.0),the accumulated inclination is about 1.8‰,less than 2.5‰as specified by the China design code.The redistribution of axial load occurs with the maximum increase of about 40%of the initial value.As the vertical load increases,the accumulated inclination can exceed 2.5‰.The inclination of pile group induced by non-symmetrical cyclic thermal loading should be well considered at the design stage.