Deformation monitoring of long GFRP bar soil nails using distributed optical fiber sensing technology

Abstract

This paper introduces a new measurement technology characterized by the use of distributed optical fiber sensor (OFSs) for monitoring the strain and temperature distribution of glass fiber reinforced polymer (GFRP) bar soil nails. Laboratory tension tests were used to verify the performance of the OFSs for strain and elongation monitoring of GFRP bars. The measured strain data from the OFSs agree fairly well with the data from strain gauges in calibration tests. In field monitoring tests, two GFRP bar soil nails were installed with OFSs and pure strain data were used to evaluate the performance of GFRP bar soil nails after installation in a practical slope. Both the strain and temperature distributions measured by the OFSs show symmetric features. A Brillouin optical time domain analysis (BOTDA) measurement unit was used to collect temperature and strain data from the OFSs. The monitoring data show that the accumulative elongations of the soil nails present a continuous but limited increase with time in the field. The achieved maximum elongations of soil nails were less than 0.4 mm. The measured axial elongations of the soil nails were also validated using corresponding data predicted by a theoretical model. The test results from the present study prove that BOTDA based sensors are useful for the investigation of the average strain distributions (or elongation) of long soil nails and these data are useful for the estimation of the potential sliding surface of the entire soil nailing system.