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A laboratory study of particle migration in cohesionless soils Moffat, Ricardo

Abstract

Filters represent a very important component of earth structures. Indeed a large percentage of embankment dam failures have involved piping or soil migration. A key aspect of filter design is evaluating the potential for internal instability. The onset of internal stability in potential unstable soils is governed by geometric and hydrodynamic constraints. Interpretations of laboratory studies o reconstituted specimens have led, in the last 25 years, to empirical criteria that define a threshold to the onset of instability. The development of those empirical criteria is reviewed. New laboratory data are then presented, and compared with selected data reported in the literature. The new data describes the response of five soil gradations to unidirectional seepage flow, at a low confining stress, from testing in a rigid walled permeameter (a Gradient Ratio device). Test variables examined include the influence of hydraulic gradient, vibration of the specimen, and opening size of the supporting wire mesh screen. The results broadly confirm the relevance of the empirical design criteria which, it is noted, address only geometric constraints to internal stability. In practice, concern exists for the risk posed by seepage flow through a potentially unstable soil: a need remains to better address hydrodynamic influences, and resulting total loss of soil.

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