The doctoral research is a study of soil filtration by geotextile fabrics, with the ultimate objective of improving design and long-term performance of underdrain systems in highways.; The experimental investigation was conducted in the laboratory using the best available techniques, the Flexible Wall Gradient Ratio Test and the Rapid Retention Test, in order to assess soil-filter compatibility and monitor geotextile clogging, for a range of materials and testing conditions. Field information was also collected and samples from highway reconstruction project were examined for their long-term performance. The main findings from these experiments relate to the influence of such factors as silt and clay amounts present in the subgrade and its state of compaction. Controlling parameters of the geotextile effectiveness are its opening size, thickness and manufacturing style. Based on these empirical results and information already available from the literature, new design and installation guidelines including filter selection criteria are proposed for non-woven geotextile filters in highway underdrain systems.
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