Abstract:
River Nile has many hydraulic structures constructed along its course from Aswan till the Mediterranean Sea. The hydraulic structures like bridges and culverts cause disturbance to the water flow resulting local scour around the structures. Scour are considered one of the main reason of the bridge failure. Although, many studies have been conducted, and researchers have adopted different approaches and particular conditions to develop design [1], There is no universal formula satisfying the conditions of the flow, sediment, river, and pier characteristics due to the complexity of the pier scour process.
Study is to help bridge authorities responsible for making a decision towards bridge scour design. Local scour around the piers is the main reason for the collapse of bridges founded in alluvial sediments. Scour prediction and reduction is a prerequisite for successful bridge design. The aim of this study is to assess the simulation and prediction of scour processes hydro-dynamically and morphologically around vertical and inclined piers. A newly version of FLOW-3D model 11.2 including three sediment transport equations were extensively used for estimating the scour around pier. The results of the model in terms of water surface, flow velocity, bed shear stress and scour depth were effectively compared with several sets of the experimental and numerical data in the literature. The model provided an accurate estimation of water surface, flow velocity and bed shear stress. However, results for the vertical velocity upstream the piers were underestimated. The predictive capability of the model was mainly depend on the pier shape and inclined direction. This study strongly demonstrates that a 3D hydro-morphological model can be effectively used to predict the scour depth around piers.
The scour depths around seven single pier configurations (circular, square and rectangular configurations, with pier length (L) to width (D) ratios of 3, 4.5, 6, 7.5, and 9) were experimentally and numerically investigated under shallow water conditions with vertical and inclined piers down stream flow direction.
The experiments were conducted to investigate the pier shape effect on local scours when the flow intensity (V/Vc) and shallowness changed. The maximum scour depth (ys/D) was highly affected by the pier length (L). The ys/D was maximized in the case of a rectangular pier, with an L/D ratio of 4.5 and a minimized L/D ratio of 7.5 and 9. The numerical results using the FLOW-3D model were used to study the effects of downflow, streamwise velocity (vx), shear stress and turbulence (i.e., energy and intensity) on the ys/D of the rectangular pier at different L/D ratios. The maximum ys/D was found at the location where high downflow, vx and shear stress occurred. A new correlation to predict the ys/D for rectangular bridge piers was developed. The correlation coefficients between the measured and predicted data were high, with an R2 of 0.913 and a root mean square error (RMSE) of 0.238. The new correlation was more accurate compared with similar ones in the literature for predicting ys/D around rectangular piers, with L/D ratios ranging from 1 to 9 under clear water conditions and an upstream water depth (h) ratio (h/D) of 1.4 to 2.35.
The inclined pier configuration reduced the ys/D of the pier. The maximum ys/D occurred at the rectangular pier with L/D of 4.5 at the vertical and inclined pier (inclined angles (θ) of 10, 15, 21 and 30°). The ys/D was significantly decreased by increasing the angle of the pier from 10 to 30°. The ys/D of inclined rectangular piers were deteriorated at reducing θ from 30 to 10° and increasing L/D ratio from 1 to 4.5. Better results for ys/D was registered for the inclined rectangular piers at θ of 30°and L/D ratio of 7.5 as compared to other shapes and inclined angles. New equations for prediction of local scour depth for circular, square and rectangular bridge piers were developed. The equations give excellent results of predicting the maximum clear water scour depth around vertical and inclined pier with inclined angles of 10, 15, 21 and 30°. The down flow, stream wise velocity, shear stress and local scour depth were significantly reduced at the inclination angle of the circular pier downstream. However, they are nearly equal to those of inclined perpendicular circular pier.
هويدا محمد أحمد خليل عمارة
الجامعة المصرية اليابانية للعلوم والتكنولوجيا – 2019
