Investigation the effect of the collar thickness on scour reduction around Bridge Pier

Local scour around bridge pier is one of the most important destruction factors of bridges. Many researchers have investigated scour around bridge pier; however, there is still not available single solution for this issue due to complexity of the problem and multiplicity of the effective factors. Different methods have been proposed to prevent or reduce scouring around bridge piers such as Riprap, collar, slot, submerge sheet and so on. According to researches, installing a collar around the base to delay the onset of scour in some cases significantly reduced the depth of scour around the base. In this study, by using the rectangular collar around the cylindrical pier, the effect of the collar thickness on scour reduction around bridge pier was investigated. The results of the experiments showed with installation of the collar not only velocity of scour is reduced but the depth of scour hole around the pier especially in downstream of the pier is also decreased. Also, with increasing collar thickness, the performance of the collar is reduced. Based on the results, the collar thickness was equal to 5 percent of the pier diameter and less than that had negligible reduction in the performance of the collar. However, the performance of the collar decreased when the collar thickness was more than 5 percent. Therefore, the appropriate thickness of the collar is proposed 5 percent of the pier diameter.