The permeability properties of geotextiles and geotextile/soil systems were studied using gradient ratio testing apparatus improving on the type of U. S. Army Engineer Waterways Experiment Station.
It is suggested that the permittivity is better than permeability to evaluate the characteristics of geotextiles as filter materials. From the results on six geotextiles, it is confirmed that the decrease of permittivity according to the surcharge load is very slight, although the thickness decreases greatly.
It is also obtained from the results of long term permeability tests for the geotextile/soil systems, that the permeability decrease with time by clogging of geotextiles. Further, the trend is approximately straight on the log-log diagram.