Field data are used to study the size distribution of bedload in paved gravel-bed streams. Similarity analysis yields the results that all grain size ranges are of approximately equal transportability when the critical condition for breaking the pavement is exceeded. This result is only approximately correct due to deviations from similarity. However, it is adequate to justify development of a method for calculating total bedload, which requires only the subpavement median grain size rather than the size distribution. A method for calculating bedload size distribution that accounts for deviation from similarity is also developed.

Closure of "Bedload and Size Distribution in Paved Gravel-Bed Streams"

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

The flow around a vertical circular pile exposed to a steady current is studied numerically and experimentally. The numerical model is a three-dimensional model. The model validation was achieved against new experimental data (which include two-component laser-Doppler anemometry (LDA) flow measurements and the hot-film bed shear stress measurements, and reported in the present paper) and the data of others, and a k-w turbulence model was used for closure. The model does not have a free-surface facility and therefore is applicable only to cases where the Froude number is small (Fr < 0(0.2)). The flow model was used to study the horseshoe vortex and lee-wake vortex flow processes around the pile. The influence on the horseshoe vortex of three parameters, namely the boundary-layer thickness, the Reynolds number and the bed roughness, was investigated. In the latter investigation, the steady solution of the model was chosen. A study of the influence of the unsteady solution on the previously mentioned flow processes was also carried out. The ranges of the parameters covered in the numerical simulations are: The boundary-layer-thickness-to-pile-diameter ratio is varied from 2 x 10 -2 to 10 2 , the pile Reynolds number from 10 2 to 2 × 10 6 , and the pile diameter-to-roughness ratio from 2 to about 10 3 . The amplification of the bed shear stress around the pile (including the areas under the horseshoe vortex and the lee-wake region) was obtained for various values of the previously mentioned parameters. The steady-state flow model was coupled with a morphologic model to calculate scour around a vertical circular pile exposed to a steady current in the case of non-cohesive sediment. The morphologic model includes (i) a two-dimensional bed load sediment-transport description, and (ii) a description of surface-layer sand slides for bed slopes exceeding the angle of repose. The results show that the present numerical simulation captures all the main features of the scour process. The equilibrium scour depth obtained from the simulation agrees well with the experiments for the upstream scour hole. Some discrepancy (up to 30 %) was observed, however, for the downstream scour hole. The calculations show that the amplification of the bed shear stress around the pile in the equilibrium state of the scour process is reduced considerably with respect to that experienced at the initial stage where the bed is plane.

Numerical and experimental investigation of flow and scour around a circular pile

Scour is the number one cause of bridge failures. Scour in coarse grained soils (sand, gravel) is relatively well known, but scour in fine grained soils (silt, clay) and weak rock is not. In coarse grained soils, scour takes place very rapidly and the scour rate is rarely an issue because one flood is likely to create the maximum scour depth. In fine grained soils, the scour process is much slower; as a result, even after a hundred years, a bridge may not experience the maximum depth of scour. Therefore, in fine grained soils it becomes necessary to predict the rate at which scour takes place. A new apparatus called the EFA (Erosion Function Apparatus; 〈http://tti.tamu.edu/geotech/scour〉) has been built and tested to measure the erosion rate of fine grained soils; the EFA can also be used to measure the erosion rate of coarse grained soils if necessary. The end of a Shelby tube sample from the bridge site is fitted through a tight opening at the bottom of a pipe with a rectangular cross section. Water flo...

Erosion function apparatus for scour rate predictions

A new method called SRICOS is proposed to predict the scour depth z versus time t around a cylindrical bridge pier of diameter D founded in clay. The steps involved are: (1) taking samples at the bridge pier site; (2) testing them in an erosion function apparatus to obtain the scour rate z versus the hydraulic shear stress applied τ; (3) predicting the maximum shear stress τmax, which will be induced around the pier by the water flowing at vo before the scour hole starts to develop; (4) using the measured z versus τ curve to obtain the initial scour rate zi corresponding to τmax; (5) predicting the maximum depth of scour zmax for the pier; (6) using zi and zmax to develop the hyperbolic function describing the scour depth z versus time t curve; and (7) reading the z versus t curve at a time corresponding to the duration of the flood to find the scour depth that will develop around that pier. A new apparatus is developed to measure the z versus t curve of step 2, a series of advanced numerical simulations ...

SRICOS: Prediction of Scour Rate in Cohesive Soils at Bridge Piers

https://rosap.ntl.bts.gov/view/dot/1024/dot_1024_DS1.pdf

Evaluating Scour at Bridges

https://rosap.ntl.bts.gov/view/dot/50281/dot_50281_DS1.pdf

Evaluating Scour at Bridges [Fourth Edition]

Evaluating Scour at Bridges. Third Edition

In 1988 The Federal Highway Administration issued FHWA Technical Advisory T5140.20 entitled Scour at Bridges. It required the States to evaluate the scour risk at all bridges over water. Accompanying the Advisory was the publication Interim Procedures for Evaluating Scour at Bridges. The Interim Procedures delineated the scour problem at highway encroachments and crossings as 1) stream instability and channel movement, 2) long term degradation or aggradation, 3) live-bed or clear-water contraction scour and 4) local scour at piers and abutments. The Interim Procedures provided guidance and equations for evaluating scour. This was the first time a manual was written that gave comprehensive methods and recommended equations for the hydraulic analysis to determine scour depths for design of foundations of new bridges or evaluation of existing bridges and to protect the river environment. Subsequently, the Interim Procedures were updated and issued as Hydraulic Engineering Circulars 18. The Fourth Edition of HEC-18 is summarized in this paper.

Comprehensive Scour Analysis at Highway Bridges HEC-18

In 1988 The Federal Highway Administration issued FHWA Technical Advisory T5140.20 entitled "Scour at Bridges". It required the States to evaluate the scour risk at all bridges over water. Accompanying the Advisory was the publication "Interim Procedures for Evaluating Scour at Bridges." The "Interim Procedures" delineated the scour problem at highway encroachments and crossings as 1) stream instability and channel movement, 2) long term degradation or aggradation, 3) live­ bed or clear-water contraction scour and 4) local scour at piers and abutments. The "Interim Procedures" provided guidance and equations for evaluating scour. This was the first time a manual was written that gave comprehensive methods and recommended equations for the hydraulic analysis to determine scour depths for design of foundations of new bridges or evaluation of existing bridges and to protect the river environment. Subsequently, the "Interim Procedures" were updated and issued as Hydraulic Engineering Circulars 18. The Fourth Edition of HEC-18 is summarized in this paper.

S. R. Davis

Papers

Evaluating Scour at Bridges

Evaluating Scour at Bridges [Fourth Edition]

Evaluating Scour at Bridges. Third Edition

Comprehensive Scour Analysis at Highway Bridges HEC-18

Comprbensive scour analysis at bigbw ay bridges hec-18