Document Type : Research Paper
Authors
Department of Water Engineering, Faculty of Agriculture, University of Birjand, Birjand, Iran.
Abstract
The local scour around the bridge piers is the main cause of their destruction. Based on this, extensive studies have been done to understand this phenomenon. Most of these studies have been done under steady flow conditions. This is while the flow in the river is unsteady. Therefore, the experiments of this research were carried out under unsteady flow conditions. The purpose of this research is to investigate the scour around the dual bridge piers at different distances of the piers from each other in a uniform flow as well as unsteady flow using symmetric hydrographs. The hydrographs used in the experiments are stepped hydrographs in 5 steps. The experiments were conducted under clear water conditions and U/UC=0.95. In all experiments, the diameter of the bridge pier (D) was constant and equal to 2.5 cm. The center-to-center distance between the dual bridge piers (S) was selected as 2D, 3D, 4D and 5D. In the unsteady flow, with increasing relative distance between the dual bridge piers, the maximum dimensionless scour depth of the first and second piers was increased and its maximum was measured at a relative distance of S/D=5 (in the range of relative distances studied in the research). But in the uniform flow, the maximum dimensionless scour depth of the first and second pier was observed at S/D=3 and S/D=4, respectively. Also, at a constant distance between the piers, increasing the peak and base flow of the hydrographs step-by-step, increased the maximum dimensionless scour depth of the first pier of dual bridge piers with an increasing rate. However, increasing the peak and base flow of the hydrographs step-by-step, increased the maximum dimensionless scour depth of the second pier with a decreasing and increasing rate, respectively.
Keywords
Barbhuiya A.K., and Dey S., Local scour at abutments: A review, Sadhana, 29 (2004) 449-476.
Bateni S.M., Vosoughifar H.R., Truce B., Jeng D.S., Estimation of clear-water local scour at pile groups using genetic expression programming and multivariate adaptive regression splines, Journal of Waterway, Port, Coastal, and Ocean Engineering 145 (2018) 1-11.
Briaud J.L., Chen H.C., Kwak K.W., Han S.W., Ting F.C.K., Multiflood and multilayer method for scour rate prediction at bridgepiers, Journal of Geotechnical and Geoenvironmental Engineering 127 (2001) 114-125.
Chang W.Y., Lai J.S., Yen C.L., Evolution of scour depth at circular bridge piers, Journal of Hydraulic Engineering 130 (2004) 905-913.
Chiew Y.M., Mechanics of riprap failure at bridge piers, Journal of Hydraulic Engineering 121 (1995) 635-643.
Chiew Y.M., and Melville B.W., Local scour around bridge piers, Journal of Hydraulic Research 25 (1987) 15-26.
Chiew Y.M., Scour protection at bridge piers, Journal of Hydraulic Engineering 118 (1992) 1260-1269.
Dey S., and Barbhuiya A.K., Time variation of scour at abutments, Journal of Hydraulic Engineering 131 (2005) 11-23.
EL-Ghorab E.A., Reduction of scour around bridge piers using a modified method for vortex reduction, Alexandria Engineering Journal 52 (2013) 467-478.
Guney M., and BorTurkben A., Experimental study of local scour around circular pier under hydrographs succeeding steady flow, In 36th IAHR World Congress, The Hague, Netherlands (2015).
Hamill L., Bridge Hydraulics, First Ed., CRC Press: USA; (1998).
Hannah C.R., Scour at pile groups, M.Sc. Thesis. Department of Civil Engineering, University of Canterbury, Christchurch, New Zealand, (1978).
Karimaei Tabarestani M., Zarrati A.R., Impact of flood hydrograph peak flow occurrence time on local scour around the bridge pier, Journal of Hydraulic Engineering 9 (2014) 15-32.
Kothyari U.C., Garde R.C.J., Ranga Raju K.G., Temporal variation of scour around circular bridge piers, Journal of Hydraulic Engineering 118 (1992) 1091-1106.
Lai J.S., Chang W.Y., Yen C.L., Maximum local scour depth at bridge piers under unsteady flow, Journal of Hydraulic Engineering 135 (2009) 609-614.
Lu J.Y., Hong J.H., Su C.C., Wang C.Y., Lai J.S., Field measurements and simulation of bridge scour depth variations during floods, Journal of Hydraulic Engineering 134 (2008) 810-821.
Lu J.Y., Shi Z.Z., Hong J.H., Lee J.J., Raikar R.V., Temporal variation of scour depth at nonuniform cylindrical piers, Journal of Hydraulic Engineering 137 (2010) 45-56.
Melville B.W., Coleman S.E., Bridge Scour, First Ed., Water Resources Publication: USA; (2000).
Nazariha M., Design relationships for maximum local scour depth for bridge pier groups, University of Ottawa, Ottawa, Ontario, Canada (1996).
Oliveto G., and Hager W.H., Temporal evolution of clear-water pier and abutment scour, Journal of Hydraulic Engineering 128 (2002) 811-820.
Raudkivi A.J., Ettema R., Clear-water scour at cylindrical piers, Journal of Hydraulic Engineering 109 (1983) 338-350.
Sadeghi F., Ramezani Y., Khozeymehnezhad H., Effect of submergence ratio of parallel wall on bridge abutment scour, Alexandria Engineering Journal 57 (2018) 2659-65.
Salamatian S.A., KarimaeiTabarestani M., Zarrati A.R., Local scour at a cylindrical bridge pier under a flood hydrograph, River Flow 2014 – the 7th International Conference on Fluvial Hydraulics, Lausanne, Switzerland (2014).
Sumer B.M., and Fredsoe J., The mechanics of scour in the marine environment, World Scientific (2002).
)