Abstract: Geosynthetics are used in filtration and drainage engineering. The key issues closely related to the safety of the project are the filtration characteristics of the geotextile filter layer under the action of stress and seepage. In order to reveal the mechanism of nonwoven geotextile filtering clay, a self-developed gradient ratio permeameter test device that can apply normal compressive stress is used to determine the permeability coefficient kT of the clay-nonwoven geotextile system, the permeability kj of each layered soil, the gradient ratio RG and the mass change of geotextile before and after the test. The filtration characteristics of the nonwoven geotextile filtering clay under different hydraulic gradients and stress levels are studied. The results show that kT and RG decrease along with time and eventually tend to a stable value. Increasing the hydraulic gradient can improve the water permeability of clay-nonwoven geotextile filter layer. And increasing the stress level will reduce the permeability but improve the soil retention of filter layer. Under the action of seepage, the protected soil layer shows that the permeability coefficient of the bottom soil layer near the nonwoven geotextile is the smallest, while the permeability coefficient of the uppermost soil layer away from the nonwoven geotextile is the largest. The clogging coefficient  has an intrinsic relationship with kT and RG. There may be a critical clogging coefficient under a specific stress-seepage action. If the clogging coefficient is greater than the value, it may cause the failure of the nonwoven geotextile filter layer.

Key words: geosynthetics, filtration, gradient ratio test, clay, nonwoven geotextile