Groups of piles are frequently used as bridge foundations. Different group configurations, characterized by different pile spacing, skew-angle, number, and arrangement of pile group columns interact differently with the flow field and lead to different scour patterns and equilibrium scour depth. There have been a number of past studies on the characterization of scouring at pile groups, but most of them report short duration scour experiments. A priori, such short durations may be postulated to inherently carry important uncertainties into existing scour predictors. In this study, 75 long-duration laboratory tests were run under steady, clear-water flow close to the threshold for initiation of sediment motion, to address the effect of time, pile spacing, skew-angle and number of pile group columns on the equilibrium scour depth. Pile groups consisted of matrical arrangements of one, two, or three columns of four rows, with spacings of 1, 2, 3, 4.5, and 6 pile diameters; the tested skew-angles were...

Measurements of pressure drop were carried out for the flow of a Newtonian fluid in $90deg$ tee junctions with sharp and round corners. Rounding the corners reduced the energy losses by between 10 and 20%, depending on the flow rate ratio, due to the reduction in the branching flow loss coefficient, whereas the straight flow basically remained unaffected. The corresponding detailed measurements of mean and turbulent velocities for a Reynolds number of 31,000 and flowrate ratio of 50% showed that rounding the corner lead to an increase in turbulence in the branch pipe. The increased turbulence diffused momentum more efficiently thus reducing the length of the recirculation by 25% with its width and strength also decreasing in magnitude. The overall effect of the increased dissipation due to turbulence and reduced dissipation due to mean flow irreversibilities in the recirculation was a decrease in the corresponding loss coefficient.

An experimental campaign of 25 long-duration (13–47 days) laboratory tests was carried out with three complex pier models under steady clear-water flow conditions. Each model, characterized by a different relation between the column and the pile-cap widths, Dc/Dpc, was tested for a variety of pile-cap positions relatively to the initial bed, Hc. The experimental data were used to describe the temporal evolution of the scour depth as a function of Hc/h (h = approach flow depth). The common criterion to stop experimental tests on complex piers was analyzed, and a new criterion was introduced. The equilibrium scour depth, dse, was calculated by extrapolation of data series. The results are used to evaluate the effect of Dc/Dpc and Hc/h on dse when the pile cap is above the bed (Situation 1), partially buried in the bed (Situation 2), and completely buried in the bed (Situation 3). The analysis includes the definition of Hc at which the maximum dse occurs through an equation that takes into account th...

At present, bridges are frequently built with geometries that consist of a column founded on a pile cap and supported by an array of piles, referred to as common complex piers or most often (as also in this paper), briefly, as complex piers. This paper addresses prediction of local scour depth at those complex piers. An experimental campaign of 48 long-duration tests was performed with seven complex pier models under steady clear-water flow conditions to quantify the influence of the relative column width, Dc/Dpc (Dc = column width, Dpc = pile cap width), the relative pile cap thickness, T/h (T = pile cap thickness, h = approach flow depth), and the pile-group configuration on the equilibrium scour depth, dse. Several tests were carried out for the possible range of variations in the pile cap position relatively to the initial bed level. The values of dse were estimated by extrapolation of the experimental data series. The performance of three methods, i.e., Auckland, HEC-18, and Florida Departmen...