Effects of Relative Column Width and Pile-Cap Elevation on Local Scour Depth around Complex Piers

Abstract

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, D c =D pc , was tested for a variety of pile-cap positions relatively to the initial bed, H c. The experimental data were used to describe the temporal evolution of the scour depth as a function of H c =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, d se , was calculated by extrapolation of data series. The results are used to evaluate the effect of D c =D pc and H c =h on d se 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 H c at which the maximum d se occurs through an equation that takes into account the D c =D pc ratio, the relative pile-cap thickness, T=h, and the column and pile-cap shapes.

Local Scour at Complex Bridge Piers in Close Proximity under Clear-Water and Live-Bed Flow Regime

“…The flow depth y 0 was fixed at 0.15 m. The pile-cap elevation was fixed at H c = 0.06 m and the base of the pile-cap was at the original bed level. This position is typical and leads to enlarged scour hole, as previous studies (Ataie-Ashtiani et al [18], Moreno et al [22], and Yang et al [28]) have shown that the scour depth is maximized when the pile-cap is near the original bed level. For each pier arrangement, a wide range of flow intensity ratios (U/U c ) were tested, from 0.9 to 4.0-5.2, to investigate scour features under both clear-water (U/U c ≤ 1) and live-bed (U/U c > 1) flow regimes.…”

“…In addition, the existence of the weir leads to upstream bed aggradation and consequently changes the relative pile-cap elevation to the original bed level. The relative pile-cap elevation has been considered as a key factor affecting the scour development and equilibrium scour depth at complex piers (Coleman [16]; Ataie-Ashtiani et al [18]; Moreno et al [22]; Yang et al [28]). Similar effects can also be caused by general bed degradation that usually occurs downstream of sluice gates.…”

“…A typical complex bridge pier often consists of a wall-like column supporting the bridge deck and superstructures, a pile-cap under the column, and a group of piles supporting the pile-cap. Complex bridge piers are usually built in close proximity to each other for large bridges with multiple lanes, parallel companion bridges (especially highway-railway Previous studies have paid much attention to current-induced scour at multiple piles (Hannah [2]; Elliott and Baker [3]; Zhao and Sheppard [4]; Sumer et al [5,6]; Ataie-Ashtiani and Beheshti [7]; Amini et al [8]; Liang et al [9]; Lança et al [10]; Das and Maxumdar [11]; Wang et al [12]; Khaple et al [13]; and Kim et al [14]) and scour at complex piers (Jones and Sheppard [15]; Coleman [16]; Sheppard and Glasser [17]; Ataie-Ashtiani et al [18]; Grimaldi and Cardoso [19]; Beheshti & Ataie-Ashtiani [20,21]; Moreno et al [22][23][24]; Ferraro et al [25]; Amini et al [26]; Baghbadorani et al [27]; and Yang et al [28]), respectively. However, there is still no solution for dealing with scenarios with multiple complex piers, indicating an obvious gap of the existing knowledge.…”

Scour development around structures with non-uniform cylindrical geometries

“…They also introduced the concept of non-dimensionalising scour using an equivalent diameter length scale which is calculated using an empirical relationship. Moreno et al (2015) recently examined the effect that different structural parameters of cylindrical based structures have on the temporal evolution of scour and concluded that the rate of scour is associated with the progressive physical presence in the scour hole evolution of one, two, or three structural components of the non-uniform cylindrical pier.…”

Discussion of “Estimation of Clear-Water Local Scour at Pile Groups Using Genetic Expression Programming and Multivariate Adaptive Regression Splines” by S. M. Bateni, H. R. Vosoughifar, B. Truce, and D. S. Jeng

“…,Lança et al (2013),Moreno et al (2014),Moreno et al (2016), andMoreno et al (2017). For t ≥ 3 day, additional data sources were:Sheppard (2003),Beheshti et al (2013),Chreties et al (2013), andKeshavarzi et al (2018).…”