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The Effect of Flow Depth on Local Scour Around Non-Uniform Cylindrical Piers Under Steady Flows

Author(s): Chuan-Yi Wang; Jen-Hao Cheng; Chia-Ling Chang; Han-Peng Shih; Yong-Jin Chen

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Keywords: Steady flow; Non-uniform pier; Pier diameter ratio; Local scour depth

Abstract: This research uses hydraulic models to measure the variation of local scour depth in order to clarify the scour mechanisms (V/Vc=0.95) for non-uniform pier diameter ratio of D/D * =0.4 and 0.7, and different initial bed levels under steady flow with various flow depths (0.2D * ~2.5D *). The research results show that the scour depth for the case with D/D * =0.4 is less than that with D/D*=0.7. Because the downflow effect decreases with a decrease of D/D * ratio, and the higher scouring retardation caused by the top of foundation when D/D * is equal to 0.4. When the initial bed level relative to the foundation top elevation remains the same, local scour depth for a D/D * ratio of0.4 is less than that for a ratio of 0.7 when the bridge foundation is unexposed. When y/D * =0.2, the scour depth is very small for a pier diameter ratio of 0.4 or 0.7. Therefore, the scour depth is dominated by the flow depth. The potential energy of flow and scour depth increases with an increase of y/D * for y/D * varying from 0.6D * to 2.2D *. The scour depth remains a constant when y/D * is greater than 2.2, indicating that the scour depth is unaffected by the flow depth. Therefore, the scour depth is affected by the projected pier width and the flow depth for a flow depth varying from 0.6 D * to 2.2 D *.


Year: 2012

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