The Laboratory study of the effect of the effective stress on decrease of permeability of the Urmia Earthfill Dam Central Clayey Core, Using the Flexible Wall Permeability apparatus

Shahr Chai Earth fill Dam is being constructed 15 km west of Urmia City, Iran. The dam comprises an impervious clayey core and two low permeability slurry Trench wall in upstream and downstream side of the dam. In this study the Permeability of the core was measured using the triaxial flexible wall permeability apparatus. Using the core material with 10.7% design water content, cylindrical Samples with 10 cm diameter and 12 cm height were compacted in the compaction Mold using the modified ASHTO method. In each test, Tree samples were installed in the triaxial cell and then confining stress, and the hydraulic gradient of 10 were applied. In each test series, with 3 identical samples, the applied effective stress was different From 50 kpa to 250 kpa, with 50 kpa stress difference between the tests. The effective stresspermeability diagram express that by increasing the effective stress from 50kpa to 250kpa, the hydraulic Conductivity of the samples decreased from 4.03x I0-10 m/s to 1.24x 10-1 i m/s, respectively. The result Showed that the effect of effective stress over the permeability insignificant in higher than 250 kpa effective stresses.