Riprap Equation for Protecting the Local Scour at Bridge Piers

초록

In this paper, the experiments to develop a riprap formula were conducted in an open channel flume having the opening ratios from 90% to 95%. The influence coefficients for the approaching angles and a riprap formula are suggested based upon the water depth, Froude number, opening ratio. The influence coefficients are changed by the variation of the length-width ratio of the pier and an appoaching angle. The riprap formula suggested in this paper can be applied to protecte the scour around the bridge piers having the semi-circular shape. The riprap size is varied based upon the pier Froude number and the ratio between water depth and pier width as well as the approaching angle. The riprap formula was compared with the existing six different formula with application about 50 different piers in Korea. The suggested formula indicates the similar riprap size compared to Richardson formula in no approaching angle but indicates the bigger riprap size in the bigger approaching angles. The suggested formula in this paper can be widely applied in the riprap design for the local scour protection around the bridge piers in Korea with the consideration of the approaching angles.