Temporal evolution of clear-water pier and abutment scour
01 Sep 2002-Journal of Hydraulic Engineering (American Society of Civil Engineers)-Vol. 128, Iss: 9, pp 811-820
TL;DR: In this article, a large variety of scour elements were considered, ranging from 1 to 60% of the channel width, and flow depths ranging from about 40% of channel width.
Abstract: Scour related to bridge hydraulics received much attention in the past decade, including its relation to flood hydrology and hydraulic processes in addition to steady flow. This paper presents new research on bridge pier and abutment scour based on a large data set collected at ETH Zurich, Switzerland. In total six different sediments were tested, of which three were uniform. Also a large variety of scour elements were considered, from 1 to 60% of the channel width, and flow depths ranging from 1 to about 40% of the channel width. Using similarity arguments and the analogy to flow resistance, an equation for temporal scour evolution is proposed and verified with the available literature data. The agreement of the present scour equation with both the VAW data and the literature data were considered sufficient in terms of river engineering accuracy, provided limitations relating to hydraulic, granulometric, and geometrical parameters are satisfied. These limitations are discussed and refer particularly to e...
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TL;DR: Alternative approaches, artificial neural networks (ANNs) and adaptive neuro-fuzzy inference system (ANFIS), are proposed to estimate the equilibrium and time-dependent scour depth with numerous reliable data base and numerical tests indicate that MLP/BP model provide a better prediction of scour Depth than RBF/OLS and ANFIS models.
189 citations
Cites background or methods from "Temporal evolution of clear-water p..."
...…and Engeldinger (1956), Hancu (1971), Ettema (1980), Jain and Fischer (1980), Chee (1982), Chiew (1984), Kothyari et al. (1992), Yanmaz and Altinbilek (1991), Graf (1995), Melville (1997), Melville and Chiew (1999), Oliveto and Hager (2002) and unpublished data from the University of Auckland....
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...The data reported by Melville and Chiew (1999), Kothyari et al. (1992) and Oliveto and Hager (2002) were used to predict scour depth at a particular time t....
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TL;DR: In this article, the authors clarified the limitations of a local scour equation recently proposed, based on extended laboratory data collected at VAW, Zurich, Switzerland, and investigated the effect of unsteady flow on scour development.
Abstract: This research intends to clarify the limitations of a local scour equation recently proposed, based on extended laboratory data collected at VAW, Zurich, Switzerland. The present project is concerned with four items: (1) clarification of the minimum laboratory dimensions required to apply Froude similitude; (2) effect of sloping abutments on scour advance; (3) extension of scour formula to spur dikes; and (4) effect of unsteady flow on scour development. These items were investigated mainly from an experimental point of view based on some 150 laboratory experiments and accounted for by a hydraulic approach. It was found that the basic scour equation mentioned may be applied provided additional limitations are specified. These are discussed in the light of the densimetric particle Froude number, the threshold Froude number, and other important parameters that influence the progress of local scour. The results of this study may be applied to practice, provided the limitations of the computational approach are respected.
167 citations
TL;DR: A comprehensive review of the up-to-date work on scour at bridge piers and abutments is presented in this article, where various mitigation countermeasures developed for bridge scour are discussed.
Abstract: Scour is one of the main causes of bridge failures. It accounts for about 60% of bridge failures in the United States. Scour failures tend to occur suddenly without prior warning and are very difficult to monitor during flood events. This paper presents a comprehensive review of the up-to-date work on scour at bridge piers and abutments. First, a general introduction of bridge scour including the current situation of bridge scour problems and different types of bridge scour is given. Then, different approaches developed for predicting bridge scour are reviewed. Numerical and laboratory models established for bridge scour studies are also presented. Moreover, laboratory experiments and field tests conducted for bridge scour are reviewed. Different techniques and instruments developed for bridge scour monitoring are also presented with their advantages, disadvantages, and relative cost summarized in a table. Finally, various mitigation countermeasures developed for bridge scour are discussed.
160 citations
TL;DR: In this paper, particle image velocimetry was used to study the internal flow features around circular bridge piers by applying both in the horizontal and vertical planes and therefore allowing for a quasi-spatial visualization of the velocity field.
Abstract: The flow around bridge structures is a recent research topic, given the significance of bridges as basic engineering infrastructures. This study investigates the internal flow features around circular bridge piers by Particle Image Velocimetry applied both in the horizontal and vertical planes and therefore allowing for a quasi-spatial visualization of the velocity field. The temporal evolution of the vertical deflected flow at the pier front and the horseshoe vortex inside the increasing scour hole were explored resulting in the velocity and vorticity profiles. This work, therefore, provides novel insight into the complex and fascinating two-phase flow around circular bridge piers placed in loose sediment and provides an experimental data basis for advanced numerical simulation.
158 citations
Cites background or methods from "Temporal evolution of clear-water p..."
...relating to the present work were formulated by Oliveto and Hager (2005). Fig. 13 Vertical position zr, max/ho of the maximum up-flow velocity versus dimensionless scour time TS with (solid line) Eq. 21 and (filled circle) test data; 0.58 £ R(2) £ 0.89 16 Exp Fluids (2007) 42:1–19...
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...…for down-flow) coordinate Zf is Zf ¼ ðzS þ zÞ ðzS þ zf 0Þ ð14Þ with z as the vertical coordinate measured from the original sediment surface, zS ‡ 0 as the scour depth according to Oliveto and Hager (2002) and zf 0 as vertical distance between the stagnation point and the original sediment surface....
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...proposed by Oliveto and Hager (2002), the dimensionless scour depth below the vortex centre is ZSv = zSv/zR, with zR = (hoD (2)) as the reference length....
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...relating to the present work were formulated by Oliveto and Hager (2005). Fig....
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...with z as the vertical coordinate measured from the original sediment surface, zS ‡ 0 as the scour depth according to Oliveto and Hager (2002) and zf 0 as vertical distance between the stagnation point and the original sediment surface. The latter can be expressed as (Unger 2006) Fig. 7 Vertical velocity profiles below the horseshoe vortex centre for runs A6, B6 and D6 from phase 2 to phase 3 (top), during phase 3 (centre) and in phase 4 (bottom) with (solid line) Eq. 7, (filled circle) test data Exp Fluids (2007) 42:1–19 11...
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TL;DR: Generalized Regression Neural Networks can be applied successfully for prediction of scour depth around circular bridge piers according to the empirical formula.
155 citations
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TL;DR: In this article, the authors studied the influence of flow duration on the depth of local scour at bridge piers in uniform sand beds and showed that the scour depth after 10% of the time to equilibrium is between about 50% and 80% of equilibrium scour depths, depending on the approach flow velocity.
Abstract: The temporal development of clear-water local scour depth at cylindrical bridge piers in uniform sand beds is considered. New data are presented and used to quantify the influence of flow duration on the depth of local scour. An equilibrium time scale (t*) is defined. The data show that both t* and the equilibrium scour depth (dse) are subject to similar influences of flow and sediment parameters, as might be expected because they are inherently interdependent. A method is given for determination of the time for development of dse for a given pier, sediment, and approach flow velocity and the concomitant estimation of the scour depth at any stage during development of the equilibrium scour hole. The results show that the scour depth after 10% of the time to equilibrium is between about 50% and 80% of the equilibrium scour depth, depending on the approach flow velocity. of local scour d se is rapidly attained in live-bed conditions, but rather more slowly in clear-water conditions (Fig. 1). Clear- water scour occurs for mean flow velocities up to the threshold velocity for bed sediment entrainment, i.e., V # Vc, while live- bed scour occurs for V > Vc. The maximum equilibrium scour depth dse)max occurs at V = Vc. In armored cobble or cohesive sediment bed streams, multiple flood events may be required before the maximum clear-water scour is reached. This may take many years. The equilibrium scour depth in live-bed con- ditions fluctuates due to the effects of bed form migration. The dashed lines in Fig. 1 represent the temporal average scour depth under live-bed conditions. The diagram also shows the time taken, te, for the equilibrium scour depth to develop. The equilibrium time, te, is the focus of this paper. It increases rapidly with flow velocity under clear-water conditions, but then decreases rapidly for live-bed scour. Existing equations for depth of local scour at bridge piers give the equilibrium depth and are therefore conservative re- garding temporal effects. For the live-bed conditions that typ- ically pertain in floods, equilibrium scour depths are appro- priate. However, where clear-water scour conditions exist, the equilibrium depth of scour may be overly conservative. Peak flood flows may last only a number of hours or a few days in the field, and short floods have insufficient time to generate equilibrium depths. For example, bridge piers situated on the floodplain may be wet for periods of less than one day during a flood; typically, clear-water conditions pertain at such sites. The actual scour may be only a small fraction of the equilib- rium scour depth, which could take weeks to fully develop. Johnson and McCuen (1991) developed an analytical model to simulate the temporal process of local scour at piers. The model was applied to a hypothetical bridge pier using a gen- erated sequence of flood flows over a 75 year period, the in- dividual storms being of 24 h duration. At the end of the 75 year period, the scour depth was still increasing.
605 citations
TL;DR: In this paper, the primary vortex in front of the bridge pier is considered to be the prime agent causing scour, and a procedure is developed for computing the temporal variation of scour depth under these conditions.
Abstract: Determination of scour depth is needed for economical design of bridge pier foundation. Currently, determination of design scour depth is mainly based on use of relationships for maximum scour depth in steady flow along with the design discharge. Computations have revealed that time taken by the design discharge to scour to its full potential is generally larger than the time for which it runs. Hence, the computation of temporal variation of scour depth should form the basis of the design. Experiments are conducted on temporal variation of scour around circular bridge piers placed in uniform, nonuniform, and stratified beds under steady and unsteady clear-water flows. Considering the primary vortex in front of the pier to be the prime agent causing scour, a procedure is developed for computing the temporal variation of scour depth under these conditions. Since the maximum scour depth is the scour depth at large time, the procedure is logically extended to obtain an expression for the same. Sediment nonuniformity and stratification are shown to have a significant effect on scour depth. The effect of these elements as well as that of unsteadiness of flow on scour depth are studied and taken into account in the proposed method of scour calculations.
234 citations
TL;DR: In this article, a time-dependent analysis of local scour depths around bridge piers has been conducted using the sediment continuity equation for the scour hole around bridge-piers.
Abstract: Estimation of maximum possible scour depth around bridge piers is an important step in the design of bridge pier foundations. Under known hydrological characteristics such as peak discharge and time-to-peak value of design flood hydrograph, smaller scour depths can be obtained compared to the equilibrium scour depths corresponding to clear water conditions. To examine such a phenomenon, time variation of local scour depths around bridge piers has to be determined. To this end, sets of experiments are performed using single cylindrical and square bridge pier models in the laboratory under clear water conditions with uniform bed materials. Semiempirical time-dependent analysis of local scour depths around bridge piers has been conducted using the sediment continuity equation for the scour hole around bridge piers. For design purposes, nondimensional scour prediction curves were prepared in terms of various sediment and flow properties.
199 citations
TL;DR: In this article, the authors investigate local scour at bridge abutments in a two-stage channel with different configurations of bridge abuts, and the experimental results confirm the validity of Melville's suggestion for the configurations tested.
Abstract: Experiments are described to investigate local scour at bridge abutments. The experiments were performed in a two-stage channel using abutments that extended different distances onto the floodplain including right up to the edge of the main channel (Melville, Type III). To ensure the largest scour depths the conditions on the floodplain upstream of the abutment were close to critical conditions for the bed material. The time evolution of the scour and the ultimate scour depth were measured. The time development of the local scour corresponded well with the theories of Ettema and Franzetti and the theory of Whitehouse for scour at horizontal cylinders in the marine environment. Melville has suggested that scour at abutments on floodplains can be approximated by scour in rectangular channels if an imaginary boundary is assumed, separating the flow in the main channel from that on the floodplain. The experimental results confirm the validity of Melville's suggestion for the configurations tested in the experiments.
140 citations