experimental study of geotextile's drainage and filteration propertis under different hydraulic gradients and confining pressures

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.