Author(s): Yifan Yang, Bruce W. Melville, Asaad Y. Shamseldin, Heide Friedrich
Linked Author(s): Yifan Yang
Keywords: Complex pier, local scour, skewness, pile-cap elevation, sediment coarseness
Abstract: A laboratory study on clear-water local scour at a complex pier is performed to investigate effects of pier skewness and the pile-cap elevation on scour depth. The model has a 3: 50 scale, and is representative of several bridge piers that failed in New Zealand in the past decades. The model pier consists of a wall-like rectangular column, a rectangular pile-cap and a 2�4 array of circular piles underneath. Tests are performed in a 45-m long, 1. 54-m wide tilting recirculating flume and in a 16. 5-m long, 2. 4-m wide non-recirculating flume. Skewness varies from 0� to 45� in 15� increments, and the pile-cap elevation relative to bed level is also varied. All the tests are performed with 30 hours duration, and the measured scour depths are extrapolated to equilibrium using validated equations. Results show that, for complex piers aligned to the flow, the maximum equilibrium scour depth occurs when the top of the pile-cap is close to the undisturbed bed level; for skewed complex piers, the equilibrium scour depth increases significantly compared with aligned ones. The increase of scour depth is proportional to the skew angle ?, and becomes less sensitive to ? when ?>30�. For skewed complex piers, the column generates most of the scour depth, if it is inserted significantly into the flow. The sediment coarseness D_e/d_50 also varies with pier skewness, and is inversely proportional to the normalized scour depth when D_e/d_50 is larger than a specific value. This phenomenon is in accordance with the previous studies, and the equations of Lee and Sturm (2009) show the best agreement with the data of the present study. In addition, the location of the maximum scour depth varies with different configurations, implying a need to arrange countermeasures accordingly
Year: 2017