G. Moradi - Assistante Proffesor,Civil Engineering Department, , University of Tabriz, , Tabriz, Iran
A. R. Abbasnejad - PhD Candidate of Geotechnical Engineering, University of Tabriz, Tabriz, Iran

Gheisaragh dam is an earth fill in East Azarbayjan province of Iran which is completed in 2005. The main problem with the dam operation is seepage with ascending rate through the foundation and abutments which leads to piping with considerable sinkholes in downstream. From the comprehensive geological studying in the dam site, it was disclosed that major part of dam foundation involved gypsum veins and pockets and gypsum marl. The chemical test of water sample obtained from piping sinkholes indicates significant increase in the amount of Mg++, Ca++ and So4-- content which is a sufficient evidence for dissolving of the gypsum veins due to the seepage through the foundation ground. In this paper, at first geotechnical features of the dam site and foundation and result of the chemical tests are investigated. Then, the causes of piping occurrence are indicated. According to importance of dam safety, the treatment methods are investigated for rehabilitation of dam foundation. Then the effect of each method is evaluated by numerical analysis. Finally, best method economically and practically is selected. In this method, impervious concrete cover is established on the upstream slope and a cement-bentonite cutoff wall is constructed in upstream heel of dam.

Gheisaragh dam, Extra Seepage, Remedial Method