In this, research heterogeneous earth dam model was built with (1V:2H) body slope in upstream and downstream dam body that had 1meter height, 4.5m length and 0.6 m width. From dam crest to upstream dam was constructed by coarse soil(20% fine soil) and from dam crest to upstream dam embanked by fine soil(60% fine soil). Dam model was built by blending fine soil and coarse soil. which first one is mixture of fine- the grained and coarse clay with identical length both of them had half of dam’s width in fundament of dam and second one was clay-core in of the base of dam which had coarse earth at it is sides. Third model was clay-core in width of dam at fundament which has drain. Water surface was drew in 30, 60 and 80 cm height water in upstream. In situation without drain toe and with drain toe was probed permeability trend. In models pheriatic line was measured by 7 well have been installed on dam body. Three situation of drain toe with 45 degree was inserted with 33, 44 and 65 Cm length in dam for the first model and second model. Experiment second model and third was performed at maximum height of water (80 cm) upstream dam. Water pressure in earth dam models was measured by 30 pizometers have been installed deferent point in flume body. Out discharge was gathered and was measured by drain box that had instructed in toe drain with galvanize plate. Result of physical model was compared by software (PLAXIS V8.5) model. Utilizing by SAS software was compared experiment physical model with PLAXIS model which the soft ware and experimental data has not significant difference statically. Also water break situation on coerce and fine soils interface has been proved. Finally, with respect to this comparison, optimum drain dimensions and also height of filter (considering the hydraulic conductivity amounts heterogeneous earth dam core and body has been obtained via cited software in laboratory models. For model no.1 and no.2 in 45 degrees drain, and index (which p is the height of toe drain and h is the height of maximum water upstream dam) have introduced as the most suitable drain. Key word : homogeneous earth dam, toe drain, filter, physical model, software model height of filter, water break, interface of soils.
