Experimental investigation of seepage velocity monitoring using heated fiber optics for detecting drainage filters clogging in river levees

Abstract

Drainage works are one of the measures for preventing seepage in river embankments. The objective of this study was to apply aDTS (active Distributed Temperature Sensing) as a monitoring tool to determine whether or not the functionality of the drainage works is maintained in good condition over a long period of time. This method combines a continuous measurement of temperature change distribution along optical fibers and an active heating of optical fiber cables. Specifically, heated optical fiber cables are laid in the longitudinal direction of the embankment between the drainage works and the embankment to measure the temperature changes in the ground along the fibers to measure the apparent heat conduction characteristics and estimate the conditions inside the embankment from these changes. As a fundamental study, we first studied filter materials to be used in the levee model experiments based on horizontal one-dimensional experiments, and organized the relationship between bulk thermal conductivity and pore velocity. Next, the change in apparent thermal conductivity in response to detection of the clogging of the filter material was determined from small levee model experiments, and the applicability of aDTS was verified in large levee model experiments. The results suggested the feasibility of using aDTS to detect clogging of the filter material in the drainage works.