Geotextiles are one of the most widely used synthetic materials in filtration and drainage applications. Since in real
applications, geotextiles are subjected to various hydraulic gradients and confining stresses, hydraulic behavior of geotextiles
under different circumstances is of great practical importance. In this study filtration and drainage properties of several
nonwoven needle-punched geotextiles with different properties and unit mass per area of 200g/m2, 400g/m2, 500g/m2 and
800g/m2, under various confining stresses and hydraulic gradients, were studied using standard permittivity
and transmissivity equipments. Prepared samples were subjected to hydraulic heads in the range of 10cm to 60cm and
confining stresses up to 1000kPa and their hydraulic behavior was investigated accordingly. In this study the flow regime
through the geotextile fibers and also the anisotropic behavior of geotextile permeability were investigated. The results show
that transmissivity will decrease exponentially with increasing the normal stress until a residual value is reached, and
permittivity and transmissivity coefficients were seen to decrease with increasing the hydraulic gradient. The flow regime has
found to be non-turbulent in all cases.The Geotextile hydraulic behavior is of great usage in the design of landfill covers,
design of embankments and irrigation structures drainage systems, and in the design of protection systems in river
engineering.