An Optical Fiber Bragg Grating Sensing System for Scour Monitoring

This paper proposes an optical fiber Bragg grating (FBG) sensing system for scour monitoring around the foundations of bridge piers and abutments. The new system introduces a uniform-strength fiber-reinforced polymer (FRP) beam that is instrumented with two FBG sensors in two sides of its neutral axis. The tensile and compressive strains of the beam are measured under a hydrodynamic pressure as water flowing around bridge foundations. By assuming equal temperatures around the uniform-strength beam, the difference in wavelength variations of the two embedded FBG sensors was found to be proportional to the square of flow velocity, which is directly related to scour. A prototype scour sensing system was designed and fabricated to test its sensing property in the laboratory. The experimental results indicate that the proposed system is sensitive to flow change and further monitor the scour process effectively, without responding to its surrounding hydrostatic and soil pressures.