Experimental Study of Local Scour around Inclined Bridge Pier Groups in Presence of Debris Accumulation under Various Hydraulic Conditions and Installation of Foundation Level

The destruction of bridges in most cases occur as a result of neglecting the role of hydraulic factor, particularly maximum scour depth. In flood events, accumulation of leaves and tree trunks in front of the bridge piers by blocking all or a part of the bridge opening, changes the flow pattern and accelerates the scouring process around the piers and eventually will change the maximum scour depth. In this paper, the effect of debris dimension on the maximum scour depth around inclined bridge pier groups was evaluated. The bridge piers under the study were two rectangular piers with 2.5×3.5 cm dimensions installed on the foundation with 10 cm width and 16 cm length at an angle of 28 degrees. Experiments were conducted for relative depth (the depth to pier width ratio) of 3.7, 5.2 and 6.6, debris relative width (the debris width to pier width ratio), 6, the relative length (debris length in flow aim to pier width), of 2 and 3, the relative thickness (debris thickness to pier width), of 0.5 and 1, under clear water condition. Comparison of results indicated that with increasing the thickness of debris raft, the maximum scour increases up to 29%. But with increasing the relative length of debris raft, maximum scour depth increases about 24% in comparison with no debris condition. Comparison of results showed a maximum scour depth increase in the presence of debris accumulation of up to 29%.