APPLICATION OF FIBER BRAGG GRATING SENSING TECHNOLOGY TO TUNNEL MONITORING

On the basis of introducing the basic principle and advantages of fiber Bragg grating(FBG)sensing technology,the layout schemes of FBG and temperature compensation technology in the Bainijing Tunnel No.3 in Kunming City are put forward.After 24-hour continuous monitoring,the influence of daylong maximal difference in temperature on the changes of the Bragg wavelength is discussed;and reliability estimation of the Bragg wavelength obtained by temperature sensing system on each monitoring tunnel cross-section is carried out.The calculation results validate the reliability of the FBG measurement system as a result that the standard errors of the Bragg wavelength are less than 14 pm.Then,the eight-month strain monitoring data illuminate that alternation of dry season and rainy season as an important factor is the reason in strain fluctuation of monitoring spots and rainy season as the main reason for the increase of strain change.Finally,an important monitoring position is determined;and the secondary lining of the tunnel is stable at present.The achieved results show that the FBG is good at measuring strain distribution of tunnels due to its excellent characteristics compared with traditional electromotive sensors and other optical fiber sensors.As a result,it is a feasible and effective method for structural health monitoring and damage detection of tunnels.