Bridge scour estimation using unconstrained distributed fiber optic sensors

Bridge scour is soil erosion around the bridge foundation (pier or abutment), which may cause foundation damage. Thus, effective, real-time, reliable, and robust monitoring methods are imperative. This study proposes a distributed fiber optic sensing method based on an ultra-weak fiber Bragg grating (UWFBG) array for scour monitoring and estimation. In this method, most of the optical fiber is installed freely on the surface of piers/abutments in spiral form. The unconstrained optical fiber can deform randomly and easily under flowing water, and the deformation can be collected by the UWFBGs written in the optical fiber. The scour estimation can be realized by analyzing the difference between signals of the optical fiber embedded in the sand and those immersed freely in the water. A series of experiments were designed and carried out to demonstrate the proposed method. The effects of flow velocity and temperature were investigated experimentally. Standard deviation was employed as the scour indicator, because it can indicate the discrete degree of signals. Experimental results show that the proposed method can estimate the scour in real time.