The present study was carried out to experimentally investigate the effect of single and double collar on development of local scouring around cylindrical bridge piers under live-bed condition. The single collar with diameter of 3 times the pier diameter placed on the streambed level and double collars one on the streambed level and one on a lower elevation were used. Tests were conducted with different flow intensities equal to 1.4, 2.0, 2.4, 2.8 and 4.0 where flow intensity is defined as the ratio of bed shear velocity to shear velocity of bed material at threshold of motion. One experiment was also carried out with flow intensity of 4.7 at which dunes were washed out and transition flow regime prevailed. The duration of the experiments was long enough to assure complete dune formations and multiple traverses of dunes through the pier location. Results showed that the scour depth fluctuated between a maximum and a minimum value due to the bed features migration. A graph was developed to show the efficiency of single and double collars at different positions and under different flow intensities. With two collars in place, the mean and maximum scour depths at the highest flow intensity, reduced by about 53% and 35% respectively. Efficiency of collar was better in lower flow intensities. Finally, based on the present results, a design table is presented for the elevation of the lower collar based on the flow intensity.

本研究旨在通过实验研究单环和双环对活床条件下圆柱形桥墩周围局部冲刷发展的影响。采用直径为桥墩直径 3 倍的单项圈置于河床平面上，采用双项圈，其中一个位于河床平面，一个位于较低标高。使用等于1.4、2.0、2.4、2.8和4.0的不同流动强度进行测试，其中流动强度定义为床剪切速度与床材料在运动阈值时的剪切速度之比。还进行了一项实验，流量强度为 4.7，沙丘被冲走，过渡流态占主导地位。实验的持续时间足够长，以确保完整的沙丘形成和多次穿越码头位置的沙丘。结果表明，由于河床特征的迁移，冲刷深度在最大值和最小值之间波动。开发了一个图表来显示单环和双环在不同位置和不同流量强度下的效率。安装两个项圈后，最高水流强度下的平均冲刷深度和最大冲刷深度分别减少了约 53% 和 35%。在较低的流量强度下，套环的效率更好。最后，根据现有结果，提出了基于水流强度的下领标高设计表。