The Study of Rate of Scour at Cylindrical, Square and Round Nosed Piers

Rate of scour adjacent to piled foundations may result in rapidly loss of skin friction and load bearing capacity of the piles. The piles may be subjected to unplanned bending stresses, from lateral loads and hydrodynamic forces. The knowledge related to the time taken by different piers to achieve a certain scour depth is limited. In this study experiments were conducted using wooden pier models in the re-circulating glass sided tilting flume  of 12,5 m length, 300 mm width and 450 mm deep. In all three tests water depth, discharge, and mean approach flow velocity in the channel were kept constant. The flume was filled with cohessionless bed material (artificial sand) average grain diameter of 0.203 mm to a uniform thickness. The scour depths observed from experiments were 30 mm, 16 mm and 14 mm in square, cylindrical and round nosed piers respectively. It was observed that, it takes more time for the cylindrical and round nosed piers to achieve scour depth of 22.2 mm and 20 mm respectively as estimated by Breusers and Raudkivi 1991. The results also showed that: it takes shorter time for a square nosed pier to achieve its empirical scour depth value of 26.7 mm. This indicates that the rate of scour depth development in square nosed pier is higher than that of the cylindrical and round nosed piers at a given time.