The Experimental Study of the Effects of River Mining Holes on the Bridge Piers

The Easiness of mining from the rivers and its low cost have increased use of these resources. In the present study, the effects of pit migration and development on the bridge inline piers were investigated experimentally. The circular and sharp rectangular shapes of the piers have been employed in this study. The results showed that the pit holes are developed to the downstream and upstream bridge piers in order to achieve sediment balance, which causes piers scouring at downstream and upstream. Also, the development of the holes towards upstream pier is more than the downstream pier. Regarding to aero-dynamical shape of the rectangular sharp nose bridge, the magnitude of the scouring hole at the up and downstream is reduced 24.5 and 31.55% respectively as compared to circular piers. Finally, the empirical relationships related to the maximum length and depth of scouring were derived. By using these relationships, the geometric and effective statistical parameters on the pier scouring, as well as the relative error percentage and RMSE of the obtained functions were evaluated and the depended graphs were depicted. It was found for both sediment dimensions, by reduction of the hole depth and Fr number, the dimensionless parameter of the H/y(the pit holes depth to flow depth) is decreased and the L/y and B/y (the pit holes length and width to flow depth) parameters are increased. Finally, the parameters affecting the maximum length and depth of the pit scouring were identified and introduced for both sharp piers.