Anisotropy in engineering materials is defined as having unlike properties in different directions. Considering the construction of earth structures, and energy induced compaction in vertical direction, the anisotropy is an unavoidable fact. The anisotropy of permeability in soils has been a well-known field since the past time, but there have been a few attempts to be accounted for in the geotechnical design. Because considering of this anisotropy, needs a lot of time and cost for measuring the properties of materials. In the present study, an attempt has been made to modify the experimental apparatus of measuring the permeability, in order to evaluate the anisotropic properties of cohesive-frictional soils. Using more than 126 tests on selected samples from cohesive-frictional soils, the effect of compaction type, the compactions’ moisture ratio, ratio of compaction, and the clay fraction have been evaluated. In this study, a sandy clay soil with gravel has been used. The most important reasons for selecting this soil are its availability, and being the first alternative for construction of homogenous earth dams. Compaction and its affecting factors i.e. moisture content, compaction type, level of compaction, as well as the clay fraction are the most important parameters in anisotropic properties of soils. Thus the effect of these parameters has been investigated in this research study. The samples have been prepared at three different moisture content i.e. 6, 9, and 12. In vibration compaction, samples with compaction ratio equal to 95%, 100%, and 105% relative to standard compaction ratio, and with clay fraction equal to 10%, 15%, and 20% have been used. In order to evaluate the effect of compaction type on the anisotropy of permeability in vibration compaction, static compaction, the samples with clay fraction equal to 15%, with dry density equal to maximum dry density have been used. Also, for investigation of effect of clay fraction on the anisotropic properties of permeability, only the vibration compaction has been used. From the experimental results, it has been seen that there is anisotropy in all samples. As the moisture content of compaction increases the permeability in the soil is decreased and the anisotropy has the increasing progress. Also, increasing the dry density to maximum dry density leads to increase in the anisotropy. Furthermore making density more than maximum dry density leads to decrease in the anisotropy. The minimum anisotropy has been seen in vibration compaction while maximum anisotropy was with static compaction. Also as the soil fine fraction increased the anisotropy of permeability increased.
