Influence of Temperature on BOTDR Used to Monitor Stabilizing Piles

Abstract

Abstract Distributed optical fiber sensors based on Brillouin scattering are emerging as valid alternatives for monitoring the health of civil structures and applications in geological engineering. The measurements are made by establishing a correlation between fiber strain and temperature in the frequency shift of Brillouin backscattered light induced by a monochromatic light pulse. The monitored strain consists of two parts: stress strain and temperature strain. This article presents an application of Brillouin optical time domain reflectometry in measuring stabilizing pile deformation over time. In the process of pile construction, the hydration heat of cement raises the temperature of the pile, thus causing errors in pile strain monitoring. So, the effect of temperature on strain should be considered. A finite element model built on the basis of monitoring objects and their geological environment is proposed to eliminate the influence of hydration heat on pile strain. The results indicated that the changed temperature resulting from hydration takes approximately three months to reach the same level as the ground temperature, in agreement with the monitoring results. The magnitude of the relative strain caused by hydration temperature was on the order of 10−4 microns and should be considered in the three-month monitoring data after the construction of piles. Factors that may affect calculation accuracy are discussed on the basis of the experimental and numerical results.