Experimental Investigation of the River Materials Mining Effect on the Scouring Around Armed Pier Groups

The scouring phenomenon around the bridge piers depends on the hydraulic properties of the flow, shape, and spacing of the pier relative to each other, the material and grading of the rivers bed. The purpose of this study was to investigate the effect of cavity, caused by materials mining, on scouring around the pier groups. Therefore, in order to reduce the negative effect of this mining, pier groups armed with cable were used. Pier groups were performed of three consecutive piers in the direction of flow. The experiments were carried out in two simple and armed modes (v shape), in sand bed with a median grain size of 0.78 mm, with a length of 4.25 meters, in a canal with 13 meters in length and 1.2 meters in width. The effect of materials mining on scouring in upstream and downstream of the mentioned pier groups was investigated under subcritical flow conditions (range 0.25-0.5). The results showed that in all experiments, materials mining from the upstream of the pier group reduced the scour maximum depth, but mining from the downstream of the pier group increased the scour maximum depth. Also, with increasing the Fraud number from 0.25 to 0.5, the scour depth was significantly increased in all piers and for two beds; without a pithole bed (a) and with a pithole bed (b). So that the least increase in scouring for A and B conditions was about 44 and 66%, respectively for the last pier in downstream pier group and the most increase in scoring was observed to be 75 and 76%, respectively for the first pier in upstream pier group.