低承台2×2能量桩基础单桩运行热力耦合特性研究

能量桩技术是一种集地源热泵和建筑桩基功能于一体的新型节能技术。为了研究能量桩在运行过程中的热力学特性及其对基础结构的影响规律,依托低承台2×2群桩基础,开展单根能量桩加热工况下的群桩基础热力响应特性现场试验,实测能量桩、对角桩及承台的温度和应变等变化规律,着重分析能量桩本身由于温度变化引起的力学特性、及其对桩周土体、邻桩和承台等结构的影响规律。研究结果表明,本文试验条件下,加热工况下低承台2×2桩基础中单根能量桩桩身中部产生的最大约束压应力值约为3.94 MPa,约为考虑桩体被完全加热和完全约束情况下的应力上限值的48%;在温降和运行桩的共同影响下,承台中部将产生约为1.05 MPa的附加拉应力(约为混凝土抗拉强度值的43.8%);在温度和上部荷载的耦合作用下,能量桩桩顶位移达-0.6 mm,约为桩径的0.6‰。

Thermo-mechanical coupling characteristics of single energy pile operation in 2×2 pile-cap foundation

The energy pile technology is a new energy-saving technology that integrates the functions of ground source heat pump and building pile foundation. In order to study the thermo-mechanical characteristics of energy piles and their effects on the other parts of pile foundation, field tests on the thermal response of a 2×2 pile-cap foundation under single pile heating conditions are carried out. The temperature and strain changes of energy piles, diagonal piles and cap are measured. The mechanical properties of the energy piles due to temperature changes, the influence laws on the soil around the pile and the structure of the cap are discussed. It is shown that the maximum constraint compressive stress of 3.94 MPa is generated in the middle of the pile during the summer operation of the energy piles. The condition of the thermal stresses associated with the complete heating and restraint of the pile provides a suitable upper bound for design, and the measured value is about 48% of the upper bound. Under the combined effects of atmospheric temperature and operating pile, an additional tensile stress of approximately 1.05 MPa (approximately 43.8% of the tensile strength of concrete) will be induced in the middle of the cap. The head displacement of the energy pile is about -0.6 mm (0.6‰ of pile diameter) under the thermo-mechanical coupling.