Abstract
The use of nonwoven geotextile filters is common in geoenvironmental and geotechnical engineering applications. The main requirements for successful performance of drainage and geotextile filters are soil retention, permeability and clogging resistance. In case of anti-clogging capabilities, the most popular method to evaluate the filtration behaviour of nonwoven geotextile in contact with soils is gradient ratio test. Also the number of constrictions of nonwoven geotextile should be determined on the basis of fibre diameter, thickness and porosity. The number of constrictions has been found to explain the different filtration behaviours of nonwoven geotextiles with similar or even the same opening sizes but different structures for various soil conditions. This paper presents the gradient ratio test program for internally unstable soil and nonwoven geotextiles with different structures. Test results show a significant impact of the number of constrictions on the filtration characteristics of geotextile. What is more some modifications to the filter design criteria are proposed based on interpretation of the experimental results.