Experimental study on the performance of coarse grain materials as scour protection

Abstract

Large scale hydraulic model tests were carried out to investigate the erosive potentials, bed stability and the performance as scour protection of wide-graded quarry-stone material with fractions ranging from 0.063 - 200 mm. Within the two phase test program the material was exposed to several wave spectra during hydraulic model tests in the Large Wave Flume of the Forschungszentrum Küste and additionally to an incrementally increased current in a closed-circuit flume at the Franzius-Institute. As result of the wave load, a maximum scour depth of S/D = 0.161 was observed after 9000 waves with a simulated storm duration of 20 h in model scale. Furthermore, fractional critical shear stresses were determined based on velocity measurements, which indicate highly selective incipient motion of individual fractions under steady current conditions. The selective mobility of this wide-graded material could not be expressed by the Shields approach.