Pier and abutment scour: integrated approach
01 Feb 1997-Journal of Hydraulic Engineering (American Society of Civil Engineers)-Vol. 123, Iss: 2, pp 125-136
TL;DR: In this paper, an integrated approach to the estimation of local scour depth at bridge piers and abutments, collectively termed bridge foundations, is presented, based on empirical relations, termed K-factors, that account for the effects on scour depths of flow depth and foundation size, flow intensity, sediment characteristics, foundation type, shape and alignment, and approach channel geometry.
Abstract: This paper summarizes many of the results from an extensive program of bridge scour research undertaken at The University of Auckland, New Zealand. An integrated approach to the estimation of local scour depth at bridge piers and abutments, collectively termed bridge foundations, is presented. The design method is based on empirical relations, termed K-factors, that account for the effects on scour depth of flow depth and foundation size, flow intensity, sediment characteristics, foundation type, shape and alignment, and approach channel geometry. The K-factors are evaluated by fitting envelope curves to existing data for piers and abutments and a new extensive data set for abutments. The new data are discussed and presented. Application of the design method is illustrated in examples.
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01 Jan 2012
TL;DR: Warm mix asphalt (WMA) has been gaining acceptance across the United States and Canada in recent years as mentioned in this paper, and many of these demonstrations were conducted with only one or two WMA technologies.
Abstract: INTROdu CTION Warm mix asphalt (WMA) has been gaining acceptance across the United States and Canada in recent years. A large number of state departments of transportation (DOTs) have hosted WMA demonstrations to determine if WMA should be allowed for state-funded paving projects. These demonstrations have shown that WMA is constructible and can reduce fuel usage and emissions associated with hot mix asphalt (HMA) production. However, many of these demonstrations were conducted with only one or two WMA technologies. Now there are over 25 commercially available WMA technologies in the United States. Most states do not approve a WMA technology for use on state-maintained roads without a welldocumented demonstration project. The WMA technology suppliers that were not part of these early demonstration projects often are required to organize a demonstration on their own to gain approval for state paving projects. A standard evaluation program for con
742 citations
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
01 Jan 2003
TL;DR: In this article, the geomorphic effects of wood in rivers arise from large, stable logs that catalyze changes in the routing and storage of both smaller wood and sediment, which can trigger changes in both river-reach morphology and the interaction between a river and its floodplain.
Abstract: —Wood has been falling into rivers for millions of years, resulting in both local effects on channel processes and integrated influences on channel form and dynamics over a wide range of spatial and temporal scales. Effects of stable pieces of wood on local channel hydraulics and sediment transport can influence rates of bank erosion, create pools, or initiate sediment deposition and bar formation. At larger spatial scales, changes in the supply of large wood can trigger changes in both river-reach morphology and the interaction between a river and its floodplain. Over long time scales, wood-rich rivers may retain more sediment and have lower sediment transport rates and steeper slopes than comparable wood-poor channels. Most geomorphic effects of wood in rivers arise from large, stable logs that catalyze changes in the routing and storage of both smaller wood and sediment. The size of a log relative to the channel provides a reasonable gauge of the potential stability of in-channel wood. Channels with a high supply of large, potentially stable wood may experience substantial vertical variability in bed elevation independent from external forcing (e.g., climate variability, temporal variations in sediment supply, or tectonic activity). In some river systems, changes in the wood regime, as described by the size and amount of wood supplied to a river, can result in effects as great as those arising from changes in the sediment supply or the discharge regimes. Consequently, an understanding of the geomorphic effects of wood is crucial for assessing the condition and potential response of forest channels.
265 citations
Cites background from "Pier and abutment scour: integrated..."
...Vertical obstructions behave like bridge abutments and piers, creating horseshoe vortices and turbulent eddies that scour the channel bed (Melville 1992, 1997), with scour depth increas- ing as the obstructed width increases relative to flow depth (Buffington et al., 2002 b)....
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TL;DR: In this article, local clearwater and live-bed scour tests were performed for a range of water depths and flow velocities with two different uniform cohesionless sediment diameters (0.27 and 0.84 mm ) and a circular pile with a diameter of 0.15 m.
Abstract: Local clear-water and live-bed scour tests were performed for a range of water depths and flow velocities with two different uniform cohesionless sediment diameters (0.27 and 0.84 mm ) and a circular pile with a diameter of 0.15 m . The tests were performed in a tilting flume ( 1.5 m wide, 1.2 m deep, and 45 m long) located in the Hydraulics Laboratory at the University of Auckland in Auckland, New Zealand. These tests extend local scour data obtained in controlled experiments to velocity ratio (V∕ Vc ) values as high as 6. This is near the velocity where the peak live-bed scour occurs for the sediment and flow conditions. Scour depth predictions are made with four different local scour equations for the conditions of the tests and the results compared with the measured values.
205 citations
Cites background or methods from "Pier and abutment scour: integrated..."
...Due to space limitations only four equations were selected for this comparison [Sheppard (2003a), CSU (Richardson and Davis 2001), Melville (1997), and Breusers et al. (1977)]....
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...Since the pile for the tests presented here was circular, D* = D. CSU Equation The Colorado State University (CSU) equation (Richardson and Davis 2001), also known as the HEC-18 equation, is Melville's equation (Melville 1997) is a function of V/Vc, D/D50 and y0/D....
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TL;DR: In this paper, the authors examined pool formation in gravel-and cobble-bed rivers in forest mountain drainage basins of northern California, southern Oregon, and southeastern Alaska, and demonstrated that the majority of pools at these study sites are formed by flow obstructions and that pool geometry and frequency largely depend on obstruction characteristics (size, type, and frequency).
Abstract: Controls on pool formation are examined in gravel- and cobble-bed rivers in forest mountain drainage basins of northern California, southern Oregon, and southeastern Alaska. We demonstrate that the majority of pools at our study sites are formed by flow obstructions and that pool geometry and frequency largely depend on obstruction characteristics (size, type, and frequency). However, the effectiveness of obstructions to induce scour also depends on channel characteristics, such as channel gradient, width:depth ratio, relative submergence (ratio of flow depth to grain size), and the calibre and rate of bed material supply. Moreover, different reach-scale channel types impose different characteristic physical processes and boundary conditions that further control the occurrence of pools within a catchment. Our findings indicate that effective management of pools and associated aquatic habitat requires consideration of a variety of factors, each of which may be more or less important depending on channel type and location within a catchment. Consequently, strategies for managing pools that are based solely on single-factor, regional target values (e.g. a certain number of wood pieces or pools per stream length) are likely to be ineffective because they do not account for the variety of local and catchment controls on pool scour and, therefore, may be of limited value for proactive management of complex ecosystems. Copyright 2002 John Wiley & Sons, Ltd.
199 citations
Cites background or methods from "Pier and abutment scour: integrated..."
...For example, the proximity of abutment-type obstructions to the channel margin creates a near-bank eddy that damps the turbulence around the obstruction, reducing the extent of scour compared to that of isolated (pier-type) obstructions (Melville, 1997)....
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...Experimental data show that greater median particle size decreases scour depth caused by vertical obstructions when the ratio of obstruction width to particle size is less than 25 (Melville, 1997)....
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...Pitched obstructions also typically form scour pools or eddy pools, while horizontal obstructions create underscour pools, and steps form plunge pools (step pools; Woodsmith and Buffington, 1996)....
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...Further details of the flow structure and scour around vertical obstructions are provided by Breusers et al. (1977), Melville and Raudkivi (1977), Melville (1997), and Thompson et al. (1998)....
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...We present previously unpublished data for Hurdygurdy Creek, Indian Creek, and Thompson Creek, which drain parts of the Siskiyou Mountains in northern California....
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References
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TL;DR: In this paper, a review of literature on model and field data is presented, and the empirical data are compared with theoretical considerations, together with a set of design suggestions together with possibilities for protection against scour.
Abstract: A “state of the art“ report on the subject of local scour around cylindrical piers is given here. After a description of the scouring process, a critical review of literature on model and field data is presented, and the empirical data are compared with theoretical considerations. The final result is a set of design suggestions together with possibilities for protection against scour.
608 citations
"Pier and abutment scour: integrated..." refers background in this paper
...It is usually accepted that the scour depth at piers is independent of flow depth effects for ylb > 3-4; see, for example, Breusers et al. (1977), Ettema (1980), and Raudkivi (1986)....
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TL;DR: In this paper, a design method for the estimation of equilibrium depths of local scour at bridge piers is presented, based upon envelope curves drawn to experimental data derived mostly from laboratory experiments.
Abstract: A design method for the estimation of equilibrium depths of local scour at bridge piers is presented. The method is based upon envelope curves drawn to experimental data derived mostly from laboratory experiments. The laboratory data include wide variations in flow velocity and depth, sediment size and gradation, and pier size, shape, and alignment. Local scour depth estimation is based upon the largest possible scour depth that can occur at a cylindrical pier, which is 2.4D, where D=thepierdiameter. According to the method, this depth is reduced using multiplying factors where clear‐water scour conditions exist, the flow depth is relatively shallow, and the sediment size is relatively coarse. In the case of nonrectangular piers, additional multiplying factors to account for pier shape and alignment are applied. The method of estimation of local scour depth is summarized in a flow chart.
565 citations
TL;DR: In this paper, the authors analyzed the effects of abutment length, flow depth, and shape and alignment on local scour depth at bridge abutments, and showed that the maximum scour depths measured in the laboratory for these cases are 2L and 10 y.
Abstract: Laboratory data for local scour depth at bridge abutments are presented. These include sufficient data to demonstrate the effects on scour depth of abutment length, flow depth, and abutment shape and alignment. In addition, some data for the effects of sediment characteristics, flow intensity, and approach channel geometry are given. The data are rationalized in terms of the ratio of abutment length to flow depth, L/y. Two limiting cases are identified. For large and small values of L/y, the abutments are termed long and short, respectively, and it is shown that the maximum scour depths measured in the laboratory for these cases are 2L and 10 y. Most actual cases of abutment scour lie between the limiting cases, and it is demonstrated that, in such situations, scour depth is proportional to the square root of the product L/y. These relationships are formulated in a simple design method, which is used on some illustrative examples. Limitations to the design method are discussed.
348 citations
01 Feb 1980
315 citations
"Pier and abutment scour: integrated..." refers background or methods in this paper
...(1961) • 1 Ettema(ll18O) • I .. GlD(I9'72) ... r1 Cbee(I982) • 1 DoDaoJ (1994) • rC1U_ (1984) ....
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...A systematic investigation of the effect of approach channel geometry on the scour at an abutment sited in a compound channel comprising flood and main channels is presented by ~e~ville and Ettema (1993) and Melville (1995)....
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...Armor layer formation within the scour hole is known to reduce scour depths, as discussed by Raudkivi and Ettema (1977). Melville and Sutherland (1988) used the ratio VIVa as a measure of flow intensity for scour with nonuniform sediments, where Va marks the transition from clear-water to live-bed conditions for a sedimenttransporting flow and is equivalent to Ve for uniform sediments....
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