Causes of Failure of Highway Cross Drainage Structures (A Case Study on Sile River Bridge Arbaminch-Ethiopia)
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Date
2015-08
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AAU
Abstract
Highway hydraulic structures perform the vital function of conveying, diverting, or
removing surface water from the road right-of-way. In this regard, various types of
drainage facilities are required to protect the roads against surface and subsurface
water. Among these, Bridges are the most indispensable and expensive highway cross
drainage structures that convey storm water under roads.
Bridge sub-structure components; Piers, Abutments and their approach embankments,
are damaged by scour during floods. Scour refers to the removal of soil, sand and
rocks from around bridge Piers or Abutments by swiftly moving flood current.
The overall objective of the research was to investigate causes of failure of the Sile
River Bridge particularly focusing on hydrologic and hydraulic factors.
The SCS Unit Hydrograph Model, HEC-RAS 4.0 Beta, HEC-18 Evaluating Scour at
Bridges, Eagle Point Auto CAD-2007 and other supporting soft wares are used to
analyze the causes of failure of the Sile River Bridge. Using these models, DEM data,
topographic survey data, meteorological and soil are analyzed and the peak discharge,
Contraction scour, Local scour at Abutments are estimated and also the adequacy of
the bridge opening is checked. The Analyses shows that, there is under estimation of
the peak discharge and opening size of the Sile River Bridge. The main failure cause of
the Sile River Bridge is Scour both contraction scour at the main channel of the bridge
opening area and local scour at the abutments which is estimated about 5.8m total
scour depth.
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Keywords
Drainage Structures, Highway Cross, Arbaminch-Ethiopia