GRAIN SIZE CRITERIA FOR PROTECTIVE FILTERS-AN ENQUIRY

Abstract

A critical review of grain size criteria for protective filters of cohesionless base soil is presented. From an analysis of the available experimental data and observations, it is shown that the finer sized base material has profound influence on grain size criteria. The allowable grain size ratio for stable filter performance increases with decreasing size of the base material. This increase is more pronounced if the grain size ratios were based on finer sized particles of filter and base materials. The uniformity coefficient of filter material increases with the decreasing sizes of base soil. A design procedure is suggested for both uniform and graded filters wherein, the influences of base particle size and the interdependency of the uniformity coefficient of filter material with the various grain size ratios of filter to base materials are taken into account.