Improved Filter Criterion for Cohesionless Soils

The capability of filters to retain cohensionless base soils is studied through a combination of a physical model of soil particle transport and statistical analysis of laboratory data. It is found that the ratio DF15/DB85, which is the parameter used in Terzaghi's criterion, is the single most significant predictor of filter performance. A clear physical interpretation of this parameter is given. A second parameter, DB95/DB75, is also found to be significant. This parameter is related to the capability of the base soil to form self‐healing layers. Based on these findings, an improved design criterion is proposed, which takes into account both DF15/DB85 and DB95/DB75.