Damage of Sefid Rud Buttress Dam Project in Iran Caused by the Magnitude 7.4 Manjil Earthquake of June 21, 1990

There are only few case histories of concrete dams that have suffered damage during strong earthquakes. The June 21, 1990 Manjil earthquake resulted in the loss of over 35,000 lives and the total destruction of the town of Manjil. Some 100,000 structures, including dams and irrigation canals, were destroyed or severely damaged. The epicenter was in the town of Manjil. The focal depth was 19 km and the magnitude Mw = 7.4. The nearest strong motion record available is from the town of Abbar, about 40 km from the dam site, where the horizontal components of the peak ground acceleration (PGA) were 0.65 g and 0.62 g and the vertical one was 0.52 g. The PGA at the dam site was estimated as 0.7 g. Sefid Rud Dam is a buttress dam with a maximum height of 106 m and a crest length of 417 m. There are twentythree 14 m wide buttresses, with a web thickness of 5 m, and two gravity type abutment blocks. Construction of the dam took place from 1958 to 1962. Damages to the dam structure consisted mainly of cracks along horizontal lift joints and of spalling of concrete along the vertical joints between buttress heads. These damage features affected the central buttresses at the level of the kink in the slope of the downstream face. On the dam crest, slabs of the carriageway suffered cracking and spalling. The dam was subjected to ground shaking, faulting and rockfalls. The different features of the damage of the dam and appurtenant structures including the gate of the intermediate level spillway are described. Very limited information can be found in the literature on this dam, which up to now is the concrete dam that has experienced the strongest ground shaking of any large concrete dam in the world. The author was a member of the official reconnaissance team inspecting the dam shortly after the earthquake. The repair works carried out after the earthquake, which included epoxy grouting of the cracks and the installation of rock anchors in all blocks are also described.