Experimental study of the effect of asymmetric T- shaped spur dike on the scour reduction in bridge abutment

Abstract
Background and objectives: Bridges are the most important river structures and lots of bridges are damaging every years by river floods. One of the reason in bridge damage is local scour in around of bridge abutment. Investigations are reveal that controlling of scour methods are based on mechanism of scour. If the design criteria perfectly do not use, extinctive damages will be occurs in bridges foundation. Proper design and management of spur dike structure can control scour and crate stability for bridge .Effect f scours on flow properties and sediment transport are different and depend on scour design parameters, flow hydrology and amount of sediment. Different factors have effected scour phenomena. For study of these factors different researches are necessary. The aim of this research are study of effective parameters on maximum scour depth in bridges abutment in asymmetric composite sections.
Material and methods: This research has contacted on a rectangular shape flume with dimension of 1 m width,12 m length and 60 cm depth in hydraulic laboratory of Shahrood University. In this research the amount of scour in cape of abutment have been studied with asymmetric T- Shaped spur dike by 4 relative conjunction of 0.2, 0.5, 2 and 5 for length of wing by the 9, 18, 27, 36 and 45 cm distance from abutment. The amount of discharges used in study were 18,20, 22, 24 and 26 litter per second.
Results: Result of study reveal that maximum depth of scour is decreasing with increasing of the upstream length of spur dike to downstream, also it is showing that depth of scour is decreasing with increasing the distance of spur dike from abutment. Decreasing of the scour depth was 100 percent with 18 lit/s discharge and 70 percent with 26 lit/s. Results also showed that dimensions of scour hole is increasing with increasing discharge. In this research assessment of hydraulic and geometric parameters like discharge, average flow velocity, depth of water, length of spur dike, length of spur wing and distance of abutment was done. Analysis of these factors led to obtain a dimensionless equation. Final results of study was a new equation to estimate maximum depth of scour around the abutment.
Conclusion: Main results of this research revealed that with increasing of the distance of spore dike from abutment amount of dike effect to abutment erosion is increasing so that depth of scour in cap of abutment is decreasing.