Bridge Foundation Scour

Abstract

Three things happen when the water starts flowing. First, a drag force and associated shear stresses develop at the interface between the soil particle and the water flowing over it. Second, the normal stress on top of the soil particle decreases because of the water flow. Indeed, as the velocity increases around the particle or the obstacle, the pressure drops to maintain conservation of energy according to Bernoulli’s principle. This phenomenon is similar to the air flow on top of an airplane wing where the pressure is lower than below the wing thereby developing the uplift force necessary for the plane to fly. Third, the normal stresses and shear stresses applied at the boundaries are fluctuating with time because of the turbulence in the water. These fluctuations find their roots in the appearance and disappearance of eddies, vortices, ejections and sweeps in the flowing water; and they can contribute significantly to the erosion process especially at higher velocities. In some cases they are the main reason of erosion...