Volume 6, Issue 4 (December 1983)
The In-Plane Permeability of Geotextiles
Since about 1965, synthetic fabrics commonly known as geotextiles have contributed to the solution of many civil engineering drainage, separation, and reinforcement problems. In recent years an effort has been made to develop general guidelines for the selection of geotextiles for various specific uses. One of these uses of geotextiles is in railroad track rehabilitation. A primary function of a geotextile for use in track rehabilitation is to facilitate the lateral drainage of excess water from the track load-bearing area to the drainage ditches. As the ballast above the geotextile becomes fouled, the importance of the in-plane drainage capability of the geotextile becomes more and more important. Accordingly, the work presented herein addresses the measurement of the in-plane permeability of geotextiles. Laboratory tests conducted over normal loads likely to be incurred in the track suggest that only thick nonwoven geotextiles are likely to possess coefficients of inplane permeability sufficient to maintain a satisfactory long-term performance. Geotextile specimens removed from beneath ballast substantiate this finding. Furthermore, tests performed on the geotextiles removed from in-track strongly suggest that better performance is obtained from those thick nonwoven geotextiles with low equivalent opening sizes (EOS). From the data it is recommended that in order to meet the in-plane permeability requirement, geotextiles for track rehabilitation be thick nonwoven geotextiles with an EOS preferably less than 40-µm (No. 400) sieve.