Brillouin Scattering Fiber Optic Sensor for Distributed Measurement of Liquid Content and Geosynthetic Strains in Subsurface

摘要

The design and functionality of optical sensing for distributed measurement of water content in soil and strains in geosythetics are presented. Sensing is based on the characteristics of Brillouin scattering at discrete positions along a single optical fiber embedded in the geomedia. The bare fiber is used in strain measurements and it is coupled with a hydrophilic polymer in water content measurements. Experiments with a prototype water content sensor demonstrated measurement of water-content up to 30% in compacted wet clay. Swelling and drying of the polymers showed that the water-content measurements were fully reversible. Experiments with an instrumented PVC geosynthetic strip showed strain measurements to be possible up to the breakage strain of the fiber (～ 3.5%) over its one-meter gauge length.