Investigation on failure of the bottom outlet of Dewana Dam – Darbandikhan, Iraq

This paper investigates the causes of failure in the bottom outlet of the Dewana dam, Darbandikhan, Iraq, and proposes rehabilitation techniques to restore its strength. The outlet is 150 m long with a cross-sectional area of approximately 9 m². Failures were reported in the slab and the walls of two 20 m segments adjacent to the core of the earth dam. Especially, the slabs in these segments suffered excessive deflection near the haunches, while excessive cracking and bar buckling were noticed in the upper part of the walls. It was found that there was a discrepancy in the gravity load calculations and that reliance on the arching effect required revision. The Halabjah earthquake may have also contributed to the failure. Constructing a new reinforced concrete outlet or filling the existing outlet with plum concrete are the proposed rehabilitation methods. The latter is preferred, as the former requires careful management. Finally, it was recommended to carry out the rehabilitation work urgently for the full length of the outlet, especially in sections where the backfill is more than 7 m.