Effect of a Stiff Thin Foundation Soil Layer's Depth on Dynamic Response of an Embankment Dam

In 2002, Zeyzoun Dam failure, that is an embankment dam located at the northwest of Syria, made a big Awareness of the effects of the lack of Geotechnical investigations and seismic conditions of the site of the dam. The dam located, in the vicinity of the Dead Sea fault, which emphasizes the importance of analyzing the effects of lithological stratum in dam foundations on dam seismic stability. This paper is concerned with the influence of a high permeable soil layer that has different static and dynamic properties, and exists at different depths in dam foundation. Numerical models arepreparedto analyze that effectbyapplying finite element method and considering seepage, dynamic analysis and slope stability. The results shows thatphreatic line rises in the dam body because of decreasing in permeable layer depth, which is resulting in two effects, The first is increasing in pore-water pressure, and destabilizing forces in dam body, The second is decreasing in stabilizing forces and factors of safety. The effective stresses decrease above phreatic line due to decreasing in suction pressure, and will decrease under phreatic line due to increasing in pore water pressure. The foundation stratum has a damping effect of decreasing the factor of safety under seismic conditions by 5%, except the case where Layer 3-1 is located near ground level (where the dam failed), where it has amplification effect.