桩顶约束下桥梁大直径能量桩热力响应现场试验

Field Test on Thermal Response of Large Diameter Energy Pile under the Pile Top Constraint

能量桩是一种绿色新技术,符合工程建设节能减排与绿色发展理念。为了研究大直径能量桩的热力学特性及结构响应,依托河南省三门峡灵宝市国道310底董桥台2×2群桩基础,在大直径灌注桩内埋设换热管形成能量桩。开展了无荷载夏季工况能量桩热响应现场试验,实测能量桩运行期间出、入水口温度、应力、回温后残余温度、温度变化量-热致应力/轴力关系、桩顶位移等变化规律。试验结果表明:三组不同流速试验下,流速增大,桩身温度、应力有小幅增大;停止试验后回温5 d后残余温度仍有16%~28%,7 d后回温残余温度约11%~17%;桩身最大应力约为3.5 MPa;能量桩桩顶累积变形-0.98 mm(约仅为桩径的0.81‰);桩顶在单桩无荷载、无荷载承台群桩约束、单桩逐级加载、恒载承台群桩约束的不同条件下,K值分别为28.6%、37.8%、43.2%和71.4%;试验流速为0.6、0.8 m/s,每平米桩-土接触面积换热量q分别是0.4 m/s流速下q的53%和128%。

Energy pile is a new green technology,in line with the concept of energy conservation and emission reduction in engineering construction and green development. In order to study the thermodynamic properties and structural response of energy piles of large diameters,a heat exchange pipe was buried in the large-diameter cast-in pile under the bearing platform to form an energy pile at the site of national G310,Lingbao city,Henan Province,2×2 pile group foundation of Didong abutment. Field tests on the thermal response of energy piles without loading in summer were carried out to measure outlet and inlet temperature,stress,residual temperature after return temperature,temperature change-thermally induced stress/axial force relationship and pile top displacement during operation of energy piles. The test results show that the temperature and stress of the pile increased slightly with the increase of flow rate under three different flow rate tests. After stopping the test,the residual temperature was still 16%-28% after 5 days of reheating,while the residual temperature after 7 days was about 11%-17%. The maximum stress along the pile was about 3.5 MPa. The cumulative deformation of the pile tip of the energy pile was-0.98mm(about 0.81‰ of the pile diameter). The values of Kh of pile top were 28.6%,37.8%,43.2% and 71.4% respectively under different conditions of single pile no-load,no-load cap pile group constraint,single pile step-by-step loading,and constant load cap pile group constraint,showing an increasing trend. The qat the flow rate of 0.6 m/s and 0.8 m/s was 53% and 128% of qat the flow rate of 0.4 m/s.