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A laboratory permeameter study of geotextile-soil retention in cyclic flow

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Title: A laboratory permeameter study of geotextile-soil retention in cyclic flow
Author: Srikongsri, Atitep
Degree Doctor of Philosophy - PhD
Program Civil Engineering
Copyright Date: 2010
Publicly Available in cIRcle 2010-05-25
Abstract: In the absence of an extensive body of laboratory and field data, empirical criteria for soil retention in dynamic or cyclic flow are not yet well-defined with reference to a margin of safety. A performance-based approach is taken in this study: the method of investigation involves laboratory tests on a total of seven geotextiles (needle-punched nonwoven and woven materials) and a total of four uniformly-graded soils (non-plastic fine sand and coarse silt). Filtration compatibility in unidirectional and cyclic flow reversal is evaluated using two rigid-wall permeameters: a small bench-mounted device, and a large floor-mounted device. Analysis of the results addresses the effects of specimen size (small and large), sidewall friction and stress distribution, and examines the influence of filter ratio (AOS/Dn), hydraulic gradient (i) and confining stress (σʹ) over a range of cyclic flow reversal times or wave period (T). A novel analytical framework is proposed from the permeameter test results, to unify AOS/Dn and a hydromechanical index that accounts for the combined effect of hydraulic gradient and confining stress. The framework provides a distinction between the benign actions of mass loss through the geotextile by washout, in contrast to the more problematic action of piping. A filter ratio AOS/D₈₅ appears better-suited to interpretation of the data than AOS/D₅₀. The framework is used to examine the margin of safety inherent in current design guidance. Independent verification of the framework through comparison with other laboratory studies, and a consideration of field observations reported by others, leads to a recommendation that AOS/D₈₅ ≤ 1 to address undue conservatism in design guidance.
URI: http://hdl.handle.net/2429/25029
Scholarly Level: Graduate

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