Soil–geotextile filter interaction under high stress levels in the gradient ratio test

Abstract

This paper presents the results of gradient ratio tests on different soil–geotextile systems under normal stresses up to 2000 kPa. Different types of soil and geotextiles were tested, and the soil particles that passed through the geotextile and those retained in it were collected for particle size analyses. The results obtained show that the use of definitions of gradient ratio based on the measurement of water heads close to the geotextile layer can be useful for a better identification of geotextile-clogging mechanisms. The entrapment of soil particles in the geotextile increases its retaining capacity and alters the conditions for further clogging. The dimensions of the entrapped soil particles can be greater than the geotextile pore dimensions under unconfined conditions and are controlled by soil and geotextile characteristics and by the soil sample preparation technique employed. The results suggest that current retention and permeability criteria for geotextile filters can be excessively conservative. Discussions on geotextile performance in the test and under field conditions are also presented as well as limitations and new proposals for the interpretation of the gradient ratio test.