Development of Fiber Bragg Grating Based Soil Pressure Transducer for Measuring Pavement Response

摘要

A soil pressure transducer by using fiber Bragg grating (FBG) sensors associated with a circular diaphragm is developed. The FBG based transducers can be used for pavement performance study and weigh-in-motion measurement. We consider three methods of bonding the FBG to the diaphragm: (i) radially, (ii) radially, inside a glass caillary, and (iii) circumferentially. The investigation of strain-gradient induced spectral broadening in FBG-based transducers is conducted since spectral broadening can have adverse effects ont he sensor interrogrations. We derive analytical closed form results for describing measurand-induced strain gradients in circular geometry transducers, which allow us to experimentally demonstrate novel FBG bonding approaches that eliminate spectral broadening. In addition, Bragg spectral broadening analysis using T-matrix calculation is also conducted to validate some of the experimental results. Two prototypes of soil pressure transducers are field tested at the Cold Region Research Engineering Laboratory (CRREL). The buried pressure transducers are impact-tested by use of a Falling-weight-Deflectometer (FWD), and detected by NRL-developed FBG interrogation device. Lastly, we use the Boussinesq equation to verify the soil stress measured by the buried transducers.