Research On Filtration Properties Of Geotextiles Affected By Uniaxial Tension

Geotextiles are commonly used to retain the soil on the upstream side while liquid pass through them in hydraulic and civil engineering. Three criteria are required for geotextile filters, including permeability criterion, retention criterion and clogging criterion. Due to the complicated nature of actual filtration, three criteria have been simplified, without considering external loading conditions. Opening size is an important factor in filtration design. Opening size has some changes under tension, which will affect the filtration of geotextile. The opening size is suitable when optimal geotextile is used in the project. If the opening size becomes smaller, the geotextile will not meet the retention criterion. If the opening size becomes larger, the geotextile will not meet permeability critetion.Filtration properties of geotextiles affected by uniaxial tension were studied on the basis of experimental and theoretical analysis. First, the opening size variation of woven geotextile under tension was determined by the Digital Image Method and the opening size variation of nonwoven geotextile under tension was determined by the Hydrodynamic Sieving Method. Then opening size formulas were derived from fiber structures. Finally filtration properties of the two kinds of geotextiles werestudied by the gradient ratio test.The Percent Open Area (POA) of woven geotextiles increases with the increase of tensile strains, and the relation of them is approximately linearity. The pore size distributions shift to the direction of the larger open sizes. Three characteristic opening sizes (i.e., O30、O50 and O95) increase with the increase of tensile strains. The change rates of characteristic opening sizes are approximately linear with the tensile strains and smaller characteristic opening sizes have larger increases with the tensile strains. The formula of opening size which is derived from fiber structure of woven geotextile can be used to calculate the Equivalent Opening Size (EOS) and the POA. The estimated values by the formulas are consistent with test results of the Digital Image Method and existing literature results.The seepage path and the opening size of nonwoven geotextile are more complex than woven geotextile. The opening size of nonwoven geotextile decreased with the increase of thickness in an unstressed state. The equivalent opening sizes of nonwoven Geotextiles decreased with the increase of tensile strains. The formula of equivalent opening size of nonwoven geotextiles under uniaxial tension was derived. The estimated values by the formula were consistent with test values and existing literature results.With the increase in the tensile strains, the flow rate through the woven geotextile becomes larger, and the percentage of soil passing through the woven geotextile becomes larger, and the value of GR/GRo decreases. When it comes to nonwoven Geotextiles, the reverse happens.Tension, the important factor in geotextile filtration application, is researched in this paper, which can promote the development of theories and test studies and can provide reference data for geotextile filtration design.