Nonwoven geotextiles have been widely used as a substitute for mineral materials to provide filtration functions in civil engineering. However, in filter systems, geotextiles are the first to be in contact with soft, saturated, and fine soils. For that reason, the selection of a geotextile filter depends on the characteristics of the geosynthetics and the base soil (e.g. grain size distribution, internal stability, permeability) and on the design and boundary conditions such as continuity of

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... soil-geotextile filter contact interface. The geotextile filter must be properly designed to avoid clogging. The most commonly method used for measuring filtration compatibility of soil-geotextile systems is the gradient ratio test. This paper presents the gradient ratio test program for needle-punched nonwoven geotextile used as a filter layer and internally unstable soil. Laboratory tests were conducted in a modified gradient ratio test apparatus. Test results show that gradient ratio increases with time due to clogging. Also the need for a measurement of water heads very close to the geotextile to measurement of water heads very close to the geotextile to provide additional information on the soil-geotextile system behaviour were presented.