2006 M.Sc. Graduated Blouchi Mohammad

The effect of collar shape on the depth and development of bridge pier scour

Abstract

Most bridges are damaged for the reason of scouring usually. A lot of methods have been used to reduce scour depth. These methods are >The experimental model was carried out in Fluid Mechanics Laboratory in the Civil engineering department in Isfahan University of Technology. Rectangle flume with length of 11 meters and 405 millimeters wide and 700 millimeters height has been used for experiments. Teflon tube with diameter of 40 millimeters was used as the pier. The bed material was consists of uniform sand with diameter of 600 to 800 micron and specific gravity of 2.65. Collars that used for experiments was collar with diameter of tow times of the pier diameter, collar with diameter of three times of the pier diameter, collar number 1 (circle with inside outgrowth), collar number 2 (eccentric circle with pier), collar number 3 (combination of semicircle and square) and collar number 4 (oval shape). The criterion that used for equilibrium depth was criterion of Kummar et all (1999).

Experiments showed that scouring begin in relative shear velocity of 0.5 for case of without collar, 0.53 for the case of collar with diameter of tow times of the pier diameter, 0.61 for the case of collar number 1 and for other shapes of collar this amount is 0.58. The time development curve can be divided to three main parts that are lag time (that scour hole haven’t reached to pier steal), the middle time (that scouring