Scour around spherical bodies and self-burial

This paper summarizes the results of an experimental study on scour around spherical bodies and self-burial in steady current and in waves. The equilibrium scour depth below a fixed sphere in steady current for live-bed conditions was found to be S/D = O(O.3) D being the sphere diameter. The effect of the Shields parameter, theta, and that of the position of the sphere with respect to the bed, e, were investigated. It was found that, under live-bed conditions, the effect of theta is quite weak. It was also found that the effect of e is significant. No scour occurs when e/D > 0.8. It was demonstrated that, in the case of waves, the Keulegan-Carpenter number, KC, is the main parameter that governs the equilibrium scour depth. S/D is always smaller in waves than in steady currents. Regarding the self-burial, the equilibrium self-burial depth in steady current was found to be e/D= O(0.5). The self-burial depth in waves is governed by KC, similar to the scour depth for a fixed sphere. e/D is always smaller in waves than in steady currents. The experiments indicated that the time scale of both the scour process and the self-burial process is a function of theta in the case of steady current, and theta and KC in the case of waves.