INFLUENCE OF CROSS-SECTION ON WAVE SCOUR AROUND PILES

The study extends the investigation of scour around circular vertical piles in waves, reported in 1992 in two works by Sumer et al. In the p resent paper, the influence of cross-sectional shape of piles on scour is studied. An extensive series of tests was carried out with two kin ds of cross sections: a circular cross section, and a square cross sec tion tested at two orientations to the flow (namely, 90-degrees orient ation and 45-degrees orientation), therefore giving three different te st configurations. The equilibrium scour depth as well as the time sca le of the scour process were investigated. Based on the present data, design equations are established relating the equilibrium scour depth, S0, to the Keulegan-Carpenter number (KC). For a given KC where KC le ss than or similar to 100, the scour depth is the largest for the squa re pile with 45-degrees orientation and smallest for the square pile w ith 90-degrees orientation, the circular-cylinder scour lying in betwe en. In all three cases, the equilibrium scour depth normalized by the pile width (S0/D) increases with increasing KC number. For KC greater than or similar to 100, however, S0/D approaches a constant value, whi ch is about 2 for the square piles and about 1.3 for the circular pile . Regarding the time scale of the scour process, this quantity is gove rned by two parameters, namely the Keulegan-Carpenter number and the S hields parameter. Given the latter two parameters, the time scale was found to be somewhat smaller in the case of the square pile with a 90- degrees orientation than those in the other two cases.