Investigation of Local Scouring around Hydrodynamic and Circular Pile Groups under the Influence of River Material Harvesting Pits

Mining activities can endanger the stability of hydraulic structures. Numerical modeling of local scouring around hydrodynamic and circular bridge pile groups, due to the action of clear water conditions via non-cohesive sediment, was performed using a computational fluid dynamics (CFD) model, a large eddy simulation (LES) turbulence model, and a van Rijn sedimentary model with FLOW-3D software. The pile groups were positioned upstream and downstream of a sand mining pit. The results showed that the scour depth around the downstream pile group was greater than that of the upstream one. Using hydrodynamic piers reduced the scour depth upstream of all piers and the material harvesting pit. The maximum reduction in scour depth was observed in front of the fifth pier, with a 29% reduction in scour depth. Additionally, for all models, as the material harvesting pit was moved downstream, the downstream turbulence was enhanced and stronger flow reversal and horseshoe vortices were detected in from of the downstream pile group. The flow patterns around the pile group showed that the presence of hydrodynamic piers in the upstream pile group leads to a decrease in the maximum flow velocity, whereas, when such piers were positioned in the downstream pile group, the velocity increases

Laboratory study of scouring around the roughened pile groups in the presence of material harvesting pits and at different Froude numbers

Harvesting the river materials can cause negative effects on the river and can intensify scouring around the bridge piers. This study investigates local scouring around roughened pile groups with gravel in the presence of harvesting pits for Froude numbers of 0.1, 0.25 and 0.5. It was found that applying roughness reduced the scour depth by 4.8 cm (73%). Due to increasing pile stability because of reducing local scouring, results show that the application of roughness to the surface of piers is a suitable, straightforward, cost-effective, and easy-to-apply method to reduce scouring. In addition, the maximum scour depth upstream and downstream of the harvesting pit occurred upstream of the initial piers. A comparison of scour areas shows that scour expansion in the transverse direction was greater than in the longitudinal direction and the amount of expansion increases when Froude number has been increased. Also, the extent of scouring around the initial piers was greater than the extent of scouring around the other piers. The maximum scour depth was 15 cm in front of the first pier and corresponded to simple piers and flow with a Froude number of 0.5