Design of Riprap Size at Bridge Abutment in a River Bend

Document Type : Original Article

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Abstract

Scouringwill be intensified at the river bend due to the existing of secondary flow in comparison with straight channels so attention to the erosion and its control and mitigation at this part of river is very important. The present paper is aimed to study and design the riprap diameter at bridge abutment in a river bend. In this study first a general non dimensional relationship was developed based on dimensional analysis at the point of incipient motion and incipient failure. Then extensive tests were conducted using three types of riprap with specific gravity of 1.51, 2.05 and 2.65 and sizes of 4.75, 9.52, 12.7 and 19.05 millimeter. Each riprap conducted under four different discharges of 0.017, 0.020, 0.023 and 0.028 m3/s. Each test was started from high flow depth and gradually lowered until the first displacement of rock was observed. The flow characteristics at this point were recorded as incipient motion. Incipient failure defined when all rocks are in motion. Applying the obtained data, formulas were developed to be applicable for design of rock size to control of Scour bridge abutment at river bend. The formulas developed in this research were compared with formulas of earlier studies on riprap at abutment for straight channels and suitable correction coefficients were suggested for these relations to be applicable at river bend.

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References

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Irrigation and Water Engineering
Volume 1, Issue 4 - Serial Number 4
September 2011
Pages 35-45

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