Influence of column width on the equilibrium scour depth at a complex pier

Lucia Couto, Mario Moreno, Antonio Muralha, Rodrigo Maia, António H. Cardoso

Monday 29 june 2015

14:35 - 14:50h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 2A. Sediment - Erosion

Experiments on local scouring around complex bridge piers were performed in steady clear-water conditions to evaluate the effect of the relative column width, Dc/Dpc (Dc = column width; Dpc = pile cap width), on equilibrium scour depth, dse, for different pile cap positions, Hc/h (Hc = distance from the initial bed level to the top of the pile cap; h = approach flow depth). Two complex pier models were tested for this purpose. These models were designed with a round-nose column founded on a rectangular round-nose pile cap, supported by two rows of cylindrical piles. In both models only Dc was changed, obtaining two relations of Dc/Dpc (0.55 and 0.40). A total of fourteen tests, run for 15 to 25 days, were carried out in a 40 m long and 2 m wide rectangular sand-bed tilting flume. A total of eight tests were performed with Model 1 (Dc/Dpc = 0.55) for different Hc/h ratios and six tests were performed with Model 2 (Dc/Dpc = 0.40) for the six most relevant positions analysed with Model 1. The dependence of the equilibrium scour depth on the relative pile cap position was identified, corroborating the findings of other studies. The results of both complex pier models allow the conclusion that the scour depth evolution and the equilibrium scour depth depend directly on Hc/h and Dc/Dpc. The relative increment in dse values, observed from the tests with Model 2 to the tests with Model 1, is influenced by the increment of the column width (i.e., increase in Dc/Dpc ratio), as the other geometric dimensions of the complex pier remain fixed.