Evaluation of Bridge-Scour Research: Abutment and Contraction Scour Processes and Prediction (2011) / Chapter Skim
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1 INTRODUCTION
1 INTRODUCTION
Pages 9-14
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From page 9... ...
The recommendations are particularly intended to be used by AASHTO in developing policies and procedures for use in addressing bridge abutment scour. The review draws upon a broad range of sources of information regarding abutment scour, including agency reports, books, and technical papers.
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From page 10... ...
Both Figures 1-1 and 1-2 indicate how flow approaching a bridge waterway converges then diverges once through it. As it does so, it passes around bluff bodies, generating, transporting, and eventually dissipating large-scale turbulence structures (large eddies shed in a recognizable pattern due to flow separation albeit intermittently with time)
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From page 11... ...
Such failures add additional complexity to waterway flow and scour, and thereby to scour-depth estimation. It can be readily appreciated from Figures 1-1 through 1-3 that scour indeed is a long-standing and vexing problem in hydraulic-engineering research, not to mention bridge foundation design.
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From page 12... ...
As would be expected, early work on abutment scour focused on the simpler and idealized situations of scour; notably, abutment scour simulated as scour at a rigid structure extending at depth into a bed of uniform sand. Commensurately, the existing relationships and guidelines apply to simplified abutment situations, such as an abutment placed in a straight rectangular channel, and are roughly based on empirical or regression equations fitted to a collection of data from laboratory tests with model abutments (whose construction does not always resemble that of actual abutments)
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From page 13... ...
They do so by not locating bridge abutments on the floodplain, but instead locating them outside the levee; in this manner, flow contraction through a bridge waterway is minimized or practically eliminated, and the abutments are not exposed to scour. On the whole, though, bridge scour continues to be a threat.
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From page 14... ...
Abutment construction influences scour, as the type of abutment affects maximum scour depth and location; and, 3. Abutment scour comprises processes of hydraulic erosion, which may cause geotechnical instability of the embankment earthfill and possibly the foundation upon which the abutment is based.
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