“Siahoo” Dam is a central clay core embankment dam with a height of about 32 meters from alluvium foundation. The dam is under construction in the east of Iran (Khorasan Province).In the main design the alluvium foundation has been removed under the core and a grouting curtain with a depth of 32 meters from bedrock has been considered to prevent the foundation from excessive seepage. The bedrock consists of highly fractured and weathered volcanic rocks (Andesit) with high permeability that in some cases reach to more than 100 lugeon. Also some artesian regions were observed in the drilling and grouting stage in the construction phase. The normal Portland cement was initially used for grouting mixture but results showed that it has not a sufficient efficiency so the fine Portland cement (with a blain more than 7000) was used for this purpose. The existing of micro cracks in the volcanic rocks was suggested to be the main reason for this phenomenon. Finally after completion of the grouting curtain, some regions of the rock foundation in the controlling drills show more permeability than design criteria. In this research the efficiency of the grouting curtain was evaluated based on the 3D saturate/unsaturated numerical seepage analysis of the dam body and foundation. The numerical methods with the assumption of a continuum media can be used with an adequate accuracy for highly fractured rocks. Results show even in a case of high permeability in some regions of the grouting curtain, the grouting curtain has a good efficiency in control the flow from the dam foundation also gradients in the downstream are in a safe manner so the uncontrolled seepage and erosion in the foundation is not expected after the reservoir filling.

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