Author(s): Mojtaba Karimaei Tabarestani, Amir Reza Zarrati, Seyed Amin Salamatian
Linked Author(s): S. Amin Salamatian
Keywords: Bridge pier, scour hole, scour countermeasure, collar efficiency, time for undermining collar
Abstract:
Collars as an effective scour countermeasure are plates, which are attached to a pier and act as a barrier to the downflow, thereby prevent its direct impingement into the streambed. Experiments show that collar cause considerable delay in scouring at the pier. There is no information can be found in the literature on how this time delay can be calculated or what its relationship with the flow and pier characteristics are. Also, no enough information is available on the scale of time for scouring development in physical models. In the present study, experiments were conducted for collar efficiency in a horizontal flume. Two different hollow Perspex circular pipes with diameter of D = 5 cm and 7 cm were used as the pier model. In addition, a round collar made from 2 mm thick Perspex sheets with an effective width, “W” equals to three times of the pier diameter was installed around the pier at the stream bed level. In each experiment, the temporal variation of scouring around the collar was recorded. In addition to the present data, experimental data from previous study for D = 4 cm were used in the analysis. Formation of scour hole around collar was monitored and different stages for scour hole development was recognized. Experimental results showed that by increasing the pier diameter, the time that the collar is undermined Tt, increases significantly. For example, in flow intensity u*/u*c = 0.91, by increasing pier width from 4 cm to 7 cm, Tt increases for about 4.4 times. In addition, experimental results showed that the effect of pier diameter on Tt is larger for lower flow intensities. Finally, from dimensional analysis and available experimental data, a new relationship is developed to calculate Tt for different diameters of bridge pier based on different important parameters affecting scour depth development. (2599, 63, 318)
Year: 2017