Monitoring and analysis of cast-in-place concrete bored piles adjacent to deep excavation by using BOTDA sensing technology

In order to monitor the deflection of bored piles, BOTDA sensing technology is employed to measure the strain and temperature profiles along three bored piles adjacent to a deep excavation. Based on the measured strain, the deflections can be calculated according to the mechanics of materials. Comparison between the deflections measured by traditional inclinometer and strain based measurement method has been fully conducted. A two-dimensional FEM model was constructed to simulate the interaction between excavation and subway tunnel and examine the deflection of the three bored piles during progressive excavation. Finally, the deflection profiles calculated from measured strains and simulated by FEM are comprehensively summarized and analysed. It can be found that the deflection changing trend at the top of the bored piles are consistent with the simulation results with acceptable errors while the deflection calculated from the measure strains has a significant discrepancy with the simulation results.