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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Water engineering : Total scour at spill-through abutments under free surface and overtopping flow conditions
Total scour at spill-through abutments under free surface and overtopping flow conditions
A laboratory study of total scour around spill-through abutments situated on the floodplain of compound channels is
presented, for situations where both local scour and contraction scour occur together. The experiments include
abutments near the main channel bank and abutments set-back from the main channel. Free surface and overtopping
flow conditions were investigated in a 45-m long recirculating laboratory flume. The tests were characterized by a livebed
scour regime in the main channel (0.46-m wide) and clear-water scour regime on the floodplain (1.08-m wide). The
test models were designed to represent a two-lane bridge at a 1:45 geometric scale. Roughness elements on the
floodplain, both upstream and downstream of the mobile section, were used to adjust the flow distribution. Riprap rocks
were placed around the abutment, based on the FHWA-NHI-09-112 (US) guidelines. Five ultrasonic depth-sounders
were used to obtain scour development in the vicinity of the abutment toe, the dynamic-equilibrium scour depth, detailed
bed-scour contour plots and sand dune heights around the abutment. A 3D down-looking velocimeter and a side-looking
acoustic Doppler velocimeter were used to measure the flow distribution upstream of the abutment. For tests with a
short set-back abutment, the development and propagation of the sand dunes significantly affect scour development and
the final scour bathymetry around the abutment, while for tests with a long set-back abutment, the effect of sand dunes
is negligible and the effect of local turbulence on scour is minimal. For overtopping flow conditions, the
countermeasures selected using the FHWA-NHI-09-112 (US) guidelines, were found to be inadequate. The need for
additional experiments, quantifying the effect of overtopping and sand dunes propagation, is emphasized.
File Size : 1,288,594 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Water engineering
Date Published : 20/08/2015
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