基于BOTDR的能源桩现场试验与承载特性分析

Test and analysis of bearing characteristics of energy pile based on BOTDR

能源桩集承受荷载和热量交换于一体,受荷载-温度联合作用,其承载性状变化异常复杂。通过上海某能源桩工程现场试验,利用基于布里渊光时域反射技术(BOTDR)的分布式光纤智能感测技术监测桩身轴力和温度变化,获取荷载与温度单一因素及联合作用下桩身轴力及桩侧摩阻力分布曲线,分析了荷载-温度联合作用下能源桩承载性状与荷载传递特征。结果表明:能源桩承载性状与普通灌注桩有一定的差别,桩身温度升高会引起桩身变形,在土体约束作用下产生较大的桩身轴力,其大小与桩身温度变化量近似呈线性关系;荷载-温度联合作用时,桩身轴力远大于受单一因素作用时的桩身轴力,由荷载-温度联合作用引起的轴力增量可达到荷载单独作用时桩身轴力的2倍及以上,同时桩身受温度升高的影响会在较大范围产生桩侧负摩阻力,而荷载作用能够明显缓解桩侧负摩阻力的产生。

The energy pile is a combination of load bearing and heat exchange.It bears the combined action of load and temperature.The bearing capacity of energy pile is very complex.Based on the energy pile engineering in Shanghai,the Brillouin optical time-domain reflectometry(BOTDR)distributed optical fiber sensing technology is used to monitor the axial force and temperature of energy pile.The axial force and side friction distribution curve of pile are obtained under the load,temperature and under the joint action of load and temperature.The bearing characteristics and load transfer characteristics of energy pile under load and temperature are analyzed.The results show that the bearing behavior of energy pile is different from the ordinary cast-in-place pile.The increase of pile temperature will cause pile deformation,and the axial force of pile will produce under the constraint of soil,which is basically linear with the change of pile temperature.Under the combined action of load and temperature,the axial force of pile is much larger than that under the action of a single factor,and the increment of axial force caused by the combined action of load and temperature can reach two times or more that of under the action of load alone.At the same time,the side negative friction of pile will be generated in a large range due to the influence of temperature rising,but the load action can obviously alleviate the generation of negative friction.