Author(s): Sepehr Karimi, Amir Reza Zarrati, Sadegh Anvari
Linked Author(s): Amir Reza Zarrati
Keywords: Scour, short contraction, long contraction, maximum scour depth, bridge pier
Abstract:
The contraction scour in a bridge crossing is evaluated by assuming a long contraction and employing sediment transport equations together with sediment and flow discharge continuity. This scour depth is then added to local and general scouring to find total scour depth at a bridge pier. In practice, the contraction length in a bridge crossing is not long. The present study is conducted to examine this assumption by comparing scouring in a short and long contraction with the same flow condition and geometry in a physical model. Experiments were carried out in a 12 m long and 0.7 5m wide horizontal bed flume. Results showed that the maximum scour depth at the edge and the scour depth at the center of a contraction entrance depend on the type of the contraction (short or long) and the flow rate. The experimental results showed that in a short contraction the local scour hole at the edges of the contraction extends at the contraction crossing and its depth even at the contraction center can be more than scouring in the long contraction. In another word, using long contraction formula for calculating the contraction scouring in a bridge crossing may lead to under estimation of scouring. Scour depth caused by the extension of the contraction edge scour hole at the center of the short contraction entrance in various flow rates was nearly 36 % more than the general scour depth in the long contraction. One experiment was also conducted with a pier located at the center of the short contraction to check the accuracy of adding up pier local scour hole and contraction scour. (2612, 65, 314)
Year: 2017