Effect of sediment gradation on scour by symmetric crossing jets: an experimental investigation

Abstract

A laboratory study with 162 experiments was designed and conducted to investigate the effect of three non-uniform sediment samples on the scour morphology by the symmetric crossing jets. The bed sediment materials with close median diameter values and different non-uniformities were utilized to investigate the scour at various crossing angles. The results were also compared with the equivalent single jet. The proper novel relationships were presented to predict the scour hole depth, and dimensions. The results showed that at a crossing angle of 30° with low and medium tailwater depth, the scour depth increases with increasing the non-uniformity of the bed materials. At the crossing angle of 30°, the armor layer was created perfectly that was thick on the bottom of the scour hole, but for the crossing angles of 70° and 110° it was thin and was a mixture of the coarse and fine particles. At low tailwater depth at the crossing angles of 70° and 110°, by increasing the non-uniformity of the sediments, the scour tended to be more asymmetric. At the high tailwater depth, for the crossing angles of 70° and 110° the scouring was less than that of the crossing angle of 30° and single jet. HIGHLIGHTS The effects of sediment gradation, have been investigated using three non-uniform sediments on the scour below two crossing jets for the first time.; The armoring phenomenon has been studied.; The scour shape is non-symmetric in some hydraulic conditions.; Novel regression formulae considering the non-uniformity parameter are developed for the scour prediction.;

Keywords

• non-uniform sediment
• regression equations
• scour below crossing jets