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

NAtioNAl CooperAtive HigHwAy reseArCH progrAm

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.

Pier and abutment scour: integrated approach

Scale effects arise due to force ratios which are not identical between a model and its real-world prototype and result in deviations between the up-scaled model and prototype observations. This review article considers mechanical, Froude and Reynolds model–prototype similarities, describes scale effects for typical hydraulic flow phenomena and discusses how scale effects are avoided, compensated or corrected. Four approaches are addressed to obtain model–prototype similarity, to quantify scale effects and to define limiting criteria under which they can be neglected. These are inspectional analysis, dimensional analysis, calibration and scale series, which are applied to landslide generated impulse waves. Tables include both limiting criteria to avoid significant scale effects and typical scales of physical hydraulic engineering models for a wide variety of hydraulic flow phenomena. The article further shows why it is challenging to model sediment transport and distensible structures in a physical hydrau...

Scale effects in physical hydraulic engineering models

Erodibility of cohesive sediment: The importance of sediment properties

Bed shear stress is a fundamental variable in river studies to link ﬂow conditions to sediment transport. It is, however, difﬁcult to estimate this variable accurately, particularly in complex ﬂow ﬁelds. This study compares shear stress estimated from the log proﬁle, drag, Reynolds and turbulent kinetic energy (TKE) approaches in a laboratory ﬂume in a simple boundary layer, over plexiglas and over sand, and in a complex ﬂow ﬁeld around deﬂectors. Results show that in a simple boundary layer, the log proﬁle estimate is always the highest. Over plexiglas, the TKE estimate was the second largest with a value 30 per cent less than the log estimate. However, over sand, the TKE estimate did not show the expected increase in shear stress. In a simple boundary layer, the Reynolds shear stress seems the most appropriate method, particularly the extrapolated value at the bed obtained from a turbulent proﬁle. In a complex ﬂow ﬁeld around deﬂectors, the TKE method provided the best estimate of shear stress as it is not affected by local streamline variations and it takes into account the increased streamwise turbulent ﬂuctuations close to the deﬂectors. It is suggested that when single-point measurements are used to estimate shear stress, the instrument should be positioned close to 0·1 of the ﬂow depth, which corresponds to the peak value height in proﬁles of Reynolds and TKE shear stress. Copyright © 2004 John Wiley & Sons, Ltd.

Comparing Different Methods of Bed Shear Stress Estimates in Simple and Complex Flow Fields

Local pier scour experiments were performed in the laboratory to investigate the effect of relative sediment size on pier scour depth using three uniform sediment sizes and three bridge pier designs at different geometric model scales. When the data from a large number of experimental and field investigations are filtered according to a Froude number criterion, the effect of relative sediment size on dimensionless pier scour depth is brought into focus. The choice of sediment size in the laboratory model distorts the value of the ratio of pier width to sediment size in comparison with the prototype which in turn causes larger values of scour depth in the laboratory than in the field. This model distortion due to sediment size is shown to be related to the scaling of the large-scale unsteadiness of the horseshoe vortex by studying the relevant time scales of its coherent structure upstream of a bridge pier using acoustic Doppler velocimeter measurements. Observations of sediment movement, probability distributions of velocity components, and phase-averaging of velocity measured upstream of a bridge pier reveal properties of coherent motions that are discussed in terms of their contribution to the relationship between dimensionless pier scour depth and the ratio of pier width to sediment size over a large range of physical scales.

Effect of Sediment Size Scaling on Physical Modeling of Bridge Pier Scour

Numerical computations and laboratory experiments are carried out to investigate the three-dimensional structure of large-scale (coherent) vortices induced by bridge abutments on a flat bed. A finite-volume numerical method is developed for solving the unsteady, three-dimensional Reynolds-averaged Navier–Stokes equations, closed with the k-ω turbulence model, in generalized curvilinear coordinates and applied to study the flow in the vicinity of a typical abutment geometry with a fixed, flat bed. The computed flowfields reveal the presence of multiple, large-scale, unsteady vortices both in the upstream, “quiescent,” region of recirculating fluid and the shear-layer emanating from the edge of the foundation. These computational findings motivated the development of a novel experimental technique for visualizing the footprints of large-scale coherent structures at the free surface. The technique relies on digital photography and employs averaging of instantaneous images over finite-size windows to extract ...

Coherent Structures in Flat-Bed Abutment Flow: Computational Fluid Dynamics Simulations and Experiments

[1] Turbidity (T) is the most ubiquitous of surrogate technologies used to estimate suspended-sediment concentration (SSC). The effects of sediment size on turbidity are well documented; however, effects from changes in particle size distributions (PSD) are rarely evaluated. Hysteresis in relations of SSC-to-turbidity (SSC∼T) for single stormflow events was observed and quantified for a dataset of 195 concurrent measurements of SSC, turbidity, discharge, velocity, and volumetric PSD collected during five stormflows in 2009–2010 on Yellow River at Gees Mill Road in metropolitan Atlanta, Georgia. Regressions of SSC-normalized turbidity (T/SSC) on concurrently measured PSD percentiles show an inverse, exponential influence of particle size on turbidity that is not constant across the size range of the PSD. The majority of the influence of PSD on T/SSC is from particles of fine silt and smaller sizes (finer than 16 µm). This study shows that small changes in the often assumed stability of the PSD are significant to SSC∼T relations. Changes of only 5 µm in the fine silt and smaller size fractions of suspended sediment PSD can produce hysteresis in the SSC∼T rating that can increase error and produce bias. Observed SSC∼T hysteresis may be an indicator of changes in sediment properties during stormflows and of potential changes in sediment sources. Trends in the PSD time series indicate that sediment transport is capacity limited for sand-sized sediment in the channel and supply limited for fine silt and smaller sediment from the hillslope.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/wrcr.20394

Hysteresis in suspended sediment to turbidity relations due to changing particle size distributions

Clear‐water scour around a bridge abutment in the floodplain of a compound channel was investigated. Experiments were conducted in a flume with a fixed‐bed main channel and a movable‐bed floodplain in which the abutment terminated. Flow depth, discharge, compound‐channel geometry, and abutment length were varied, and measurements of approach velocity distribution and scour depth were obtained. A preliminary relationship for the dimensionless scour depth is suggested to illustrate the compound‐channel effects on scour. The proposed relationship is limited to the range of values covered by the variables in this study.

Clear‐Water Scour around Abutments in Floodplains

Two separate large eddy simulations (LES) are carried out to investigate the effects of accurate computation of the curvilinear water-surface deformation of the flow through a bridge contraction. One LES employs the rigid-lid boundary condition at the water surface, while the other uses a highly accurate level-set method (LSM), which allows the water surface to adjust itself freely in response to the flow. The simulation with the LSM is validated with data from complementary physical model tests under analogous geometrical and flow conditions. Streamwise velocity, bed-shear stress and second-order turbulence statistics obtained from both simulations are compared, and it is shown that the turbulence structure of this flow is influenced strongly by the water-surface deformation. While bed-shear stresses and first-order statistics are very similar for both cases, the instantaneous turbulence structure and consequently, the second-order statistics, are distinctly different. The correct prediction of the water-surface deformation of such flows is deemed important for the accuracy of their simulation.


Read More: http://ascelibrary.org/doi/10.1061/%28ASCE%29HY.1943-7900.0001028

Terry W. Sturm

Papers

Effect of Sediment Size Scaling on Physical Modeling of Bridge Pier Scour

Coherent Structures in Flat-Bed Abutment Flow: Computational Fluid Dynamics Simulations and Experiments

Hysteresis in suspended sediment to turbidity relations due to changing particle size distributions

Clear‐Water Scour around Abutments in Floodplains

Free-Surface versus Rigid-Lid LES Computations for Bridge-Abutment Flow