Design methods for granular filters—critical review

Abstract

Filters are used to control seepage, and to act as a barrier for preventing base soil erosion. This study is a review of past research into filtration which includes empirical, theoretical and geometric–probabilistic methods. Empirical methods are those involving laboratory testing of many base-soil–filter combinations to determine guidelines for safe filters. Theoretical packing methods determine the maximum size of particles which can fit through idealized models of the filter material. Geometric–probabilistic methods mathematically simulate the filtration process using models of pore voids and statistical techniques to determine the penetration of base particles into the filter. These methods attempt to explain base–filter interaction during filtration. In this paper, filtration of cohesive materials is discussed including problems associated with concentrated leaks and dispersive soils. Broadly graded and gap-graded materials also require individual attention, and methods to identify and deal with their problems are presented. More significantly, a recommended design procedure for filters is described, based on empirical criteria and the newly emerging geometric–probabilistic methods.