Numerical investigation of mining pit effects on maximum scour depth around bridge pier with different shape

Sand and gravel harvesting in river beds for construction purposes generates a mining pit which may change the river morphology. If the mining pit approaches the infrastructure's foundation like bridge piers influences the scour process around it. A FLOW-3D numerical simulation was provided in the present study to predict maximum scour depth around the bridge pier with a downstream mining pit with different pit heights, distances from the pier, and pier shapes. Ten experimental tests and fifty-one numerical runs were performed. The run time of the numerical analyses, grid sizes, and the turbulence models k-ε, k-ε RNG, and LES were evaluated to choose the optimal values. Also, the numerical results were verified with the experimental results and have a less than 10% error which indicates the excellent performance of the numerical model. It was observed that in both cases without a mining pit and with it, the highest value of d_s/D occurred in the circle pier shape, and the lowest values reached in the airfoil shape. The results indicate that maximum scour depth around the cylindrical bridge pier increases with increasing pit height and reducing pit distances from the pier, which can be considered in practical works in river beds.