Strain Monitoring on PHC Pipe Piles Based on Fiber Bragg Grating Sensors

Fiber Bragg grating (FBG) sensors emerged as a relatively new strain-sensing technology for civil engineering applications. This study presents a field test to assess the feasibility of FBG sensors in monitoring the strain profile of prestressed high-strength concrete (PHC) pipe piles during installation. Two open-ended PHC pipe piles were instrumented with FBG sensors and then driven into the ground using a hydraulic jacking machine. To measure the strain profile along the test piles, nine FBG sensors were arranged in a single optical fiber and then mounted on one pile at the opposite side to monitor the strain at different levels as a function of wavelength shift. The procedure for installing the FBG sensors along the PHC pipe piles is introduced first. Next, the distribution of the axial forces and average side shear stresses that were evaluated from the strain measurements of the FBG sensors are discussed. The field test results indicate that the FBG sensor system was suitable for monitoring the strain state of PHC pipe piles during installation. The axial forces and side shear stresses along the test piles were influenced significantly by the penetration depth and the local soil resistance.