Scour Monitoring System Using Fiber Bragg Grating Sensors and Water-Swellable Polymers

Abstract

Bridge scour has emerged as a significant concern worldwide, especially in the United States; approximately 60% of bridge failures are scour related. Because of the difficulty of bridge-scour inspection, scour-induced failures tend to occur suddenly without prior warning or signs of distress to the structures. A reliable, effective, and robust monitoring system is very desirable. Therefore, the present study aimed to develop an innovative scour monitoring system using fiber Bragg grating (FBG) sensors and water-swellable polymers. The polymer material swells to several times the original volume upon the absorption of water, and the expansion induces a measurable tension on the FBG sensor. The scour monitoring system is vertically embedded in soil, and the measured wavelength shifting of a particular sensor is able to indicate that the sensor is no longer covered with soil (i.e., the soil level has decreased to the elevation of that particular sensor). A detailed introduction of the sensor design was presented, including specially designed protection to prevent water from entering the sensor unit before the sensor system is in place. A prototype of the sensor system was fabricated, and several tests were conducted in the laboratory to verify the functionality of the device. The results indicate that the system is capable of monitoring the change of soil level. Furthermore, the repeatability of the polymer swelling implies the capability of monitoring the entire scour process in the long term. In addition, the proposed system concept could also be used for subsea pipeline scour monitoring and other types of chemical sensing by interchanging the polymer with materials sensitive to other measurands, such as oil.