Pore size for needle-punched nonwoven geotextiles under unequal biaxial tensile strains

Pumping pressures on geotextile tubes and differential settlement of soils typically induce unequal biaxial tensile strains in geotextiles. The effects of unequal biaxial tensile strains on the pore size of three continuous filament needle-punched geotextiles and three staple fibre needle-punched geotextiles were examined via wet sieving tests. Four groups of unequal biaxial tensile strains were evaluated, with the ratios of the strain in the machine direction of a geotextile to that in the cross-machine direction set to 1, 2, 3, and 4, respectively. The strains in the machine direction for the four groups were the same (10%, 20% and 30%). The variations of pore size distribution (PSD), O90, O65 and the porosity of strained geotextiles with the strains were analysed. The relationships of the filtration properties with pore size and porosity were also analysed. It is shown that for the same strain ratio, the PSD curves shift toward the direction of small pore sizes with increasing strain, and the values of O90, O65, and porosity decrease with increasing strain. The gradient ratio was negatively correlated with both pore size and porosity, while the permeability of the soil–geotextile system and soil loss exhibited positive correlations with pore size and porosity.