Study on the hydraulic properties of internally unstable soil-nonwoven geotextile systems: Boundary values and preliminary estimates

Internally unstable soils can pose severe conditions to granular and geotextile filters in geotechnical engineering works. Regarding the latter, several researchers have investigated the behaviour of such filters in contact with internally unstable soils and severe clogging and flow rate reductions of soil-geotextile filter systems have been observed in several cases. This paper presents a study on the prediction of boundary values for hydraulic properties of nonwoven geotextile filters in cohesionless internally unstable soils. A broad survey on results of filtration tests present in the literature was carried out for the development of a database for the study. The results obtained show that significant reductions in soil-geotextile system permeability coefficient and flow rate may occur independent on the type of test carried out, quite often as a consequence of poor hydraulic behaviour of the soil rather than geotextile filter clogging. The study has identified the level of importance of relevant parameters to assess potential malfunction of the soil-geotextile system and equations were developed to predict lower bound values and estimates of soil-geotextile system permeability coefficient for preliminary analyses.