Monitoring and analysis of PHC pipe piles under hydraulic jacking using FBG sensing technology

• The FBG sensor has been used for pipe pile monitoring for the first time.
• Axial force on the piles was calculated at different penetration depths.
• The axial force is significantly influenced by the resistance of soil layers.
• Average shear stress along the pile was calculated based on measured strains.
• The average shear stress was significantly affected by the penetration depths.

Pretensioned high-strength concrete (PHC) pipe piles have been widely used for geotechnical engineering such as foundation engineering, slope engineering, highway engineering. To study the performance of a PHC pipe pile under hydraulic jacking, the monitoring of the strain profile along the PHC pipe pile under hydraulic jacking was carried out using FBG sensing technology. In this study, a PHC pipe pile was instrumented with two series of fiber Bragg grating (FBG) sensors along pile axial direction and was then installed in the field using a hydraulic jacking method. To monitor the variation of strains along a PHC pile, two series of eight FBG strain sensors with different peak wavelengths were mounted on opposite sides of the pile with one meter spacing. In addition, based on the pile theory, both the axial force of the pile and average shear stress on the pile surface are calculated using the measured axial strains. It is found that there were significant residual strains in the piles after installation when hydraulic force was removed. This study confirms that the fiber Bragg grating (FBG) sensors are suitable for monitoring strain distribution along a pile under hydraulic jacking.