On the Local Scour around Group Piers in Series by Experimental Tests

In this research a physical model is presented. A trapezoidal shape of channel with 1.45 m width, 1 meter depth and banks slope of 1H: 1.5V was used. Circular piers (6, 8 and 10cm diameter) were tested under three different flow discharges of 50, 65 and 80 lit/s and three different median bed material sizes equal to 0.94, 1.31 and 2.12 mm. Seven different longitude distance to pier diameter ratios (1, 1.5, 2, 2.5, 3, 4 and 5) were tested. Measurement of scour depth (upstream, around and downstream of pier) was accomplished in 10, 15, 20, 30, 60, 120, 240 and 360 minutes from the beginning of each test. The results showed that 30% to 40%, 55% to 65% and more than 90% of local scour occurs at first two minutes, at first 10 minutes and 120 to 200 minutes from the beginning of test respectively. The effect of different parameter especially the distance between piers on scour depth at group piers in series was evaluated and the results were compared to other investigators. It was found that our results is best fitted with the general form of well known Sheppard et al. (2004)’s equation.