| The detection of pile foundation engineering has the characteristics of concealment,multiple influencing factors,high destructiveness,and difficult implementation,which makes traditional mechanical and electronic detection instruments face many problems in the detection and monitoring of pile foundation engineering due to the limitations of their own properties.Fiber Bragg Grating(FBG)sensing technology,as one of the most advanced online detection technologies,can realize the measurement of physical parameters such as temperature,stress,strain,and refractive index.Due to its advantages of small size,anti-electromagnetic interference,and high sensitivity,it has been used in the field of health monitoring of pile foundation engineering in recent years.However,due to the problems of poor mechanical properties,high production costs,and complex sensing signal demodulation of FBG,its application in pile foundation engineering has been severely affected.Therefore,this paper takes pile foundation health monitoring as the application background,aims to develop high-performance fiber grating sensors and arrays,and focuses on the production,encapsulation of FBG and its application in pile foundation engineering.The designed and prepared FBG sensors and arrays for pile foundation health monitoring and PM-FBG multi-parameter sensors are presented.The main work and research results of this thesis are as follows:(1)Customized writing of fiber gratings has been achieved based on hydrogen-loaded fiber and phase mask method.The effects of laser divergence angle and refractive index distribution within the fiber core on FBG fabrication were studied.By adjusting the distance between the fiber core and the phase mask and applying axial tension to the fiber,the problem of writing multiple FBGs with different central wavelengths on a single phase mask was solved,reducing the production cost of FBG arrays.(2)A study was conducted to address the low sensitivity and susceptibility to damage of fiber optic grating sensors in the health monitoring of pile foundation structures.Different structural fiber optic grating sensors were developed and packaged using various methods,including embedded FBG strain sensors,temperature sensors,and FBG array sensing cables.The changes in stress and strain of square piles were analyzed by embedding FBG array sensing cables in concrete piles,and the development process of internal cracks in square piles was discussed.FBG array sensing cables were also embedded in drilled shafts constructed using the drilling and grouting method for a foundation self-balancing static load test.The monitoring results of FBG array sensing cables,distributed sensing fiber optics,and vibrating wire strain gauges were compared and analyzed.(3)To address the complexity,large volume and weight,and high production costs associated with multi-parameter FBG sensors and sensing systems,a new type of multi-parameter sensor based on polarization-maintaining fiber Bragg gratings(PM-FBG)was developed using 3D printing fused deposition modeling.The PM-FBG sensor enables dynamic detection of temperature,displacement,and torsion of the structural surface.The sensing performance of the PM-FBG sensor was calibrated,and its sensitivity to temperature,displacement,and torsion was found to be superior to that of commercial FBG sensors.To address the issues associated with FBG sensors in pile foundation health monitoring,a pile foundation model testing platform was constructed,and the PM-FBG multiparameter sensor was used to monitor the cracking and settlement processes on the surface of the pile foundation model. |
PDF Full Text Request