GEOTEXTILE FILTER CRITERIA

Abstract

In the past decade, drainage fabric performance has been the subject of numerous research projects. Two general conclusions can be drawn from the many research findings: (a) both woven and nonwoven fabrics can provide acceptable filtration performance in drainage applications, and (b) soil and hydraulic conditions influence fabric filter properties necessary for optimum performance. More specific observations are made in this paper concerning the relation between fabric and soil properties versus drain fabric performance. These observations include the following: (a) fabric equivalent opening size (EOS) and permeability coefficients do not indicate clogging potential, (b) fabric EOS provides an indirect indication of retention ability, (c) gap-graded soils and high hydraulic gradient conditions are conducive to soil piping and filter clogging, (d) well-graded soils and low hydraulic gradients are not conducive to soil piping, and (e) fabric clogging potential can be determined by testing soil-fabric systems in simulated drainage tests that model expected use conditions. The state of the art in drainage fabric technology is reviewed, and rational filter criteria for geotextiles based on three performance parameters--retention ability, permeability, and clogging resistance--are recommended. (Author)