循环温度场作用下PCC能量桩热力学特性模型试验研究

Experimental research on thermomechanical characteristics of PCC energy pile under cyclic temperature field

PCC能量桩是河海大学岩土所开发的一种新型能量桩技术。在常规桩基静载荷模型试验基础上,将PCC能量桩放置在南京典型砂土中,并通过导热管内水体的循环对模型桩体施加温度场,以模拟PCC能量桩在实际运行过程中的承载力特性与受力机制,PCC能量桩先加载至工作荷载(极限荷载的一半),再施加热-冷循环一次,最后加载至极限荷载,测得不同温度下PCC能量桩的荷载-位移关系曲线、桩身应力-应变关系曲线等变化规律。试验结果表明,能量桩换热过程中,热量更容易从桩体传向土体(即夏季模式的热循环);热循环及制冷循环都明显改变了桩顶位移值,且往复循环作用下产生的塑性变形不能完全恢复,其积累变形可能危害上部结构安全;桩身受温度场作用产生的热应力相对较大,且不同约束条件下其变化值有所差异;在制冷循环下,桩底部甚至可能产生较大拉应力。

PCC energy pile is based on one of new type energy pile technology methods developed by Geotechnical Engineering Institute of Hohai University. On the basis of traditional static load test of pile, PCC energy piles are embedded into Nanjing typical sand. Thermal field of model pile is simulated through water circulation in the cyclic pipe. The characteristic and mechanism of bearing capacity of PCC energy pile in operation are studied. The PCC energy pile is firstly loaded to the working load（half of the ugtimate load） and then the heating and cooling cycle is applied. After that the model pile is loaded to the u〉imate load. The curves of load-displacement and stress-strain of pile shaft under different temperatures are measured. The resu〉s show that the heat can easily transfer from pile to soil（summer mode）. The displacement of pile top changes obviously during heating and cooling cycles. The change of temperature brings plastic deformation in the soil, which can harm the upper structure. The thermal stress in the PCC pile caused by temperature field is relatively large. The change of thermal stress is different under different constraint conditions. Under cooling cycle, tensile strain even appears on the bottom of pile.