Factors affecting geotextile filter long-term behaviour and their relevance in design

Geotextile and granular filters are widely used in civil (e.g. earth dams, embankments, drainage trenches, etc.) and environmental (e.g. landfills, permeable reactive barriers, etc.) engineering works. Geotextile filters are considered to be an effective alternative to conventional granular filters whose function is to prevent the movement of fine particles from the base soil allowing the liquid to flow as freely as possible. The design of a geotextile filter requires the knowledge of the base soil–filter interaction that is a very complex process due to the large number of factors involved. In this paper, the complex cases of geotextile filter design in contact with internally unstable cohesionless soils and in critical/severe applications are analysed based on recent research also developed by the authors. Moreover, the influence of the main factors affecting geotextile/filter long-term behaviour which are generally neglected in current design criteria, such as vertical effective stress, partial clogging, flow conditions, type of contact at the interface and type of permeant, are examined. Furthermore, various performance tests to evaluate the long-term soil–geotextile filter behaviour and the reliability and limits of different design criteria for cohesionless soils are discussed.