Filtration behaviour of staple fibre geotextiles under unequal biaxial tensile strains

Gradient ratio tests were conducted to investigate the filtration behaviour of staple fibre needle-punched nonwoven geotextiles subjected to unequal biaxial tensile strains. Three groups of biaxial tensile strains were designed, with the ratios of the strain in the machine direction to that in the cross-machine direction set to 1, 2, and 4, respectively. The strains in the machine direction in the three groups were the same, ranging from 10% to 30%. The tested filtration properties included the gradient ratio (GR), permeability of the soil-geotextile system, mass of soil loss, and permittivity of the pure geotextiles. Comparisons were made between the filtration properties of staple fibre (SN) geotextiles and continuous filament (CN) geotextiles. It is shown that for a certain strain ratio, the GR value at the time of test termination increases with increasing strain, and the permeability of the soil-geotextile system, soil loss, and permittivity of the pure geotextiles decrease with increasing strain. The soil loss and permittivity under equal biaxial tensile strains tend to be higher than those under unequal biaxial tensile strains. The CN geotextiles have better retention capability and more clogging potential for the tested soils than the SN geotextiles for a similar mass per unit area.