Fiber optic monitoring and performance evaluation of geotechnical structures.

摘要

Although health monitoring of civil infrastructures using fiber optic sensors has drawn increasingly attention, the potential of fiber optic monitoring in geotechnical applications is still not well identified. The advantages of fiber Bragg grating (FBG) sensors in accuracy and reliability make them exceptionally attractive for monitoring strains, temperatures, displacements, etc. of geotechnical structures.;This research has therefore commenced to develop and apply FBG based sensors for geotechnical structures in both laboratory and field conditions, together with conventional transducers. Firstly, a variety of FBG based sensors were developed and fabricated for strain, displacement and temperature measurements. Calibration test results show that the FBG based sensors are reliable for monitoring geotechnical structures with high accuracy. Secondly, the FBG sensors have been installed on steel and glass fiber reinforced polymer (GFRP) soil nails for measuring strain distributions along nail lengths during field pullout tests, respectively. Typical test data indicate that the pullout resistance has an empirical relationship with N value in standard penetration tests (SPTs). The pullout-displacement relationships before failure can be fitted by hyperbolic functions, based on which a simplified pullout model can be established. Thirdly, newly developed FBG sensing bars have been embedded in the physical models of Wudu Dam and Shuangjiangkou Cavern Group for monitoring internal displacements. The monitoring results from FBG sensing bars were in good agreement with those from conventional sensors. The comparison between experimental and numerical results verifies the reliability of these sensors and leads to some conclusions on the deformation and overall stability conditions of the geotechnical structures under investigation. Finally, a monitoring system consisting of various FBG sensors has been applied for monitoring a mat foundation and a newly stabilized slope. Implications on the current foundation design assumptions are discussed on the basis of the monitoring results. The long-term slope monitoring results indicate that slope movements fluctuated with time and that the strains and stresses in soil nails had the same tendency as the rainfall magnitude. The soldier piles at the slope toe came to play a role in resisting the potential sliding after the slope movements towards downhill accumulated to certain values.