International Review of Civil Engineering (I.RE.C.E.), Vol. xx, n. x November 2012 Manuscript received and revised xx 2010, accepted xx 2010 Copyright © 2010 Praise Worthy Prize S.r.l. - All rights reserved EXPERIMENTAL STUDY OF CHARACTERISTICS OF TOP SEEPAGE LINE THROUGH HOMOGENOUS EARTH DAM USING HELE-SHAW MODEL Dr. Raad Hoobi Irzooki 1 , Asmaa Abdul-Jabbar Jamel 2 Abstract – This investigation concerns to study the characteristics of phreatic line of seepage through homogenous earth dam with and without horizontal filter using Hele-Shaw model, which also named the viscous flow analog. The constructed and used viscous flow analog was verified by comparing the phreatic line and unit discharge for different cases of earth dams which were measured from this analog with the phreatic line and unit discharge which were obtained using computer program SEEP/W (which is a sub-program of Geo-Studio). The comparison gives a good agreement between the results of these two methods Using Hele-Shaw model, Experiments were carried out with three different viscous oils in order to present three different permeabilities of soil, for each oil there was three downstream slopes of the dam. Different runs were carried out using different upstream slopes, three variable filter lengths and three different upstream reservoir heads. For each run the downstream cover, quantity of seepage and the configuration of top seepage line were determined. Dimensional analysis was used with helping of the experimental results to develop an empirical equation in order to determine the most effective filter length which used to eliminate the downstream cover. Results from the experiments show that the downstream cover is increased with decreasing the upstream slope, downstream slope and upstream reservoir head, while it is decreased when the filter length is decreased. The results indicated that the unit discharge through the earth dam body increases with decreasing the upstream slope, and downstream slope, while it is increase with increasing the horizontal filter length, and the upstream and reservoir head. Also, the results appear the unit discharge through earth dam body increases with increasing the hydraulic conductivity, this the unit discharge for earth dam of high hydraulic conductivity affected strongly by the geometry of this dam, while this affecting is limited for the soils of low hydraulic conductivity. Copyright © 2012 Praise Worthy Prize S.r.l. - All rights reserved. Keywords: : Phreatic Surface, Homogenous Earth Dam, Horizontal Filters, Hele-Shaw Model, Downstream Slope Cover. Nomenclature a = half width between the two plates (L). B= bottom width of earth dam (L). d = downstream slope cover (L). g = acceleration of gravity (L/T 2 ). H= height of earth dam (L). h = upstream reservoir head (L). ℎ  = dimensionless, hydraulic gradient (head loss/length over which head loss occurs). k = hydraulic conductivity of dam soil (L/T). k m = hydraulic conductivity of the model L = filter length (L). V m = Main velocity of the flow in the model (L/T). α = angel of downstream slope. ѵ = fluid kinematic viscosity (L 2 /T). θ = angel of upstream slope. I. Introduction Dams, which are constructed from earth and rock materials, are generally referred to as embankment dams or fill-type dams. The history of construction of embankment dams is much older than that of concrete dams. It is evident that some earth dams were constructed about 3,000 years ago in the cradles of ancient cultures such as east countries [1]. A purely homogeneous type of dam is composed entirely of a single type of material. For a completely homogeneous section, it is inevitable that seepage emergence will occur in the downstream slope. The horizontal filter is provided over that portion of the foundation downstream from the impervious zone of the dam where high upward seepage forces exist. The filter must be pervious to drain off effectively and its design should fulfill the usual filter criteria, in order to prevent