Abstract
A modified theoretical model has been proposed to predict the pore size characteristics of nonwoven geotextiles under certain uniaxial tensile strains, considering the difference between the out‐of‐plane Poisson’s ratio and the in‐plane Poisson’s ratio of geotextiles. The pore size distributions (PSDs) and O95 subjected to different levels of uniaxial tensile strains in two needle‐punched nonwoven geotextiles have been investigated by the dry sieving test. The variation of the fibre orientation with tensile strains and the corresponding effect on pore sizes has been evaluated by image analysis. The out‐of‐plane Poisson’s ratio and the in‐plane Poisson’s ratio of geotextiles have been examined. A comparison has been made between the predictions of the original and the modified models. It is shown that the modified model can more accurately predict the decreasing rate of the PSDs, O95, and O98 than the original one. The corrected theoretical O95 and O98 under certain strains can provide a reference for the filtration design under engineering strains. The fibres reorientating to the loading direction result in the increase of the directional parameter with increasing tensile strains, which leads to the decrease of pore sizes. The theoretical PSDs are sensitive to the variation of directional parameter.
Highlights
Nonwoven geotextiles are widely used as filtration and drainage materials in various fields [1]
Many kinds of porous media have been employed in the experiments to prove the validity of these models, including nonwoven heat-bonded geotextiles, hybrid needle punched nonwoven geotextiles, spunbonded nonwoven geotextiles, thermally bonded nonwoven structures, and glass mat [12, 13, 15,16,17,18,19,20,21,22,23]. e fibre orientation distribution is an important parameter in the model, which needs to be estimated by image analysis [17,18,19,20]
The randomly distributed fibres reorientate to the loading direction in Figure 4, which agrees with the histograms of relative frequency of fibres for NW100, as shown in Figure 5. e relative frequency at 0° increases from 0.14 to 0.24 for NW100 and from 0.08 to 0.16 for NW200, when the strain increases from 0% to 10%
Summary
Nonwoven geotextiles are widely used as filtration and drainage materials in various fields [1]. E filtration applications of geotextiles are typically subjected to tensile strains and result in noticeable variations of pore size and permeability in nonwoven geotextiles [8,9,10,11,12,13,14]. Erefore, accurate determination of pore sizes at certain tensile strains is essential in the filtration design of nonwoven geotextiles. Ere is still limited theoretical model to predict the effect of uniaxial tensile strain on the pore sizes in geotextiles [13, 14]. Due to the Advances in Civil Engineering fact that the microscopes can typically focus on limited layers of the fibres, the samples employed in the literature were relatively thin, which were generally less than 250 g/m2 [13,14,15,16,17,18,19,20,21,22,23]. If the sample is relatively thick, the fibres in deep layers will be blurry and cannot be evaluated with an optical microscope
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