Experimental Study of the Applications of Fiber Optic Distributed Temperature Sensors in Detecting Seepage in Soils

摘要

Fiber optic distributed temperature sensors (FODTS), based on Brillouin and Raman scattering, have been successfully used in various applications such as fire detection, petroleum pipeline leakage detection, and concrete dam crack monitoring. In recent years, FODTS have been used to monitor the seepage of reservoirs, earth dams, water channels, embankments, tunnels, and levees. Unlike other applications, monitoring the seepage of these structures involves acquiring, processing, and analyzing the temperature information of porous media that are mainly rocks and soils. Detailed studies on the thermal interaction among rocks/soils, water, and optic fibers are essential to improve judgment on the occurrence of seepage and explore the possibility of quantifying the seepage rate. This paper describes a large-scale experimental study that investigated the thermal interaction. The study was carried out on three different soils (i.e., poorly graded gravel, poorly graded sand, and silty sand) in both non-seepage and seepage conditions. The effects of soil types, moisture content, seepage rates, and heat source powers on temperature changes were assessed in this study. It was found that, with a heat source, FODTS could effectively detect seepage under most circumstances. The temperature change differs in different soils. For all the soils investigated, the moisture content and the heat power showed significant influence on the temperature change. The seepage rate has insignificant influence on temperature change.