保压蜗壳外围混凝土应变及脱空分布式光纤监测

Distributed Optical Fiber Sensor based Monitoring on Surrounding Concrete Strain and Gap Width of Preloading Spiral Case

采用基于PPP-BOTDA分布式光纤应变感测技术,将特制的感测光缆安装到水轮机保压蜗壳表面及外围混凝土内,对充水试验和保压卸压过程中蜗壳结构的应变分布和变化进行监测,实测光纤应变量与计算结果接近。当充水试验加压到2.6MPa和4.1MPa时,钢蜗壳表面的环向平均实测应变分别为330με和590με。感测光缆有效监测到了蜗壳在首次加压到1MPa时的应力调整现象,以及卸压后约-20με的残余应变。试验中还观察到了卸压后外围混凝土的收缩,混凝土结构环向压应变约为70~100με,计算得到蜗壳和混凝土脱空的隙缝开度为0.5~1.4mm,监测成果可为蜗壳结构的设计优化提供参考。

Sensing optical cables were installed on the surface of a steel spiral case and into the surrounding concrete to monitor the strain distribution during a water-filling test and a preloading-unloading program based on PPP-BOTDA distributed optical fiber sensing technology.The monitored strain was close to the calculated strain.When the water-filling pressures were 2.6 MPa and 4.1MPa,the average hoop strains of the spiral case were about 330μεand 590με,respectively.With sensing cables,it was the first time that the stress adjustment of the spiral case was monitored when inner pressure increased to 1MPa and the residual strain of-20μεwas obtained after preloading.Meanwhile,the shrinkage of the surrounding concrete was effectively monitored during depressurization.The measured hoop strain of concrete was 70με-100με,according to which the width of the gap between the steel plate and concrete was estimated to be 0.5-1.4mm.The monitoring results by PPP-BOTDA provide references for the optimal design and safety monitoring of the spiral case structure.