The Variation In Pore Size Characteristics And Permeability Of Geotextiles Subjected To Tensile Strain

Geotextiles have been widely used as filter materials in numerous geotechnical applications,sucha as flood prevention,coastal engineering,environment protection and urban construction.To assure filtration performance,the geotextile filtration design criteria involves soil retention capability,permeability and anti-clogging function.The various pore sizes on the pore size distribution curve reflect not only soil retention capability but also the permeability of geotextile.As a result,pore size distribution curve is an important parameter in filter design.In the practice of geotechnical applications,geotextile are subjected to various tensile strains.It is important to prevent filtration damage caused by geotextile pore failure under tensioning engineering.This paper investigates variation in different pore sizes of woven geotextiles,needle punched staple-fiber nonvoven geotextiles and needle punched filament-fiber nonwoven geotextiles by image analysis method,dry sieving method and bubble point test.The tested specimens are subjected by uniaxial tensioning,laterally confined tensioning and unsymmetrically biaxial tensioning.Furthermore,this paper measures the permeability coefficients of woven and nonwoven geotextiles under various tensile strains by vertical permeability test.The relationship between geotextile permeability coefficients under tensioning and the different pore sizes is proposed in this paper.1)Theoretical formulae of the woven geotextile pore size distribution probability based on pore number percentage have been established under uniaxial tensioning,laterally confined tensioning and unsymmetrically biaxial tensioning.For woven geotextiles,the pore size deformation and position of pores are monitored during tensioning by image analysis method,and the number and percentage of pore sizes are counted.The pore size distribution probability has good consistency of Gaussian distribution curve.The theoretical formula of pore size distribution（PSD）curve has been integrated by Gaussian distribution.And the theoretical PSD curve agrees well with experimental PSD results.The variation in theoretical characteristic pore sizes has been calculated by adopting Gaussian curve parameter into pore size expression and PSD expression.The theoretical pore sizes has good consistency of experimental pore sizes.2)Theoretical formulae of the nonwoven geotextile pore size distribution probability based on sieving particle mass percentage have been established under laterally confined tensioning.For needle-punched staple-fiber nonwoven geotextiles,this paper proposes the theoretical formulae of pore size distribution probability based on sieving particle mass percentag under laterally confined tensioning.The theoretical analysis considers the angles of special fibers rather than the planar pore size distribution of fibers.The pore size distribution curves of needle-punched staple-fiber nonwoven geotextiles have been obtained by dry sieving test after eliminating electrostatic influence.The theoretical PSD curves of the needle-punched staple-fiber nonwoven geotextiles are in good agreement with the experimental PSD results.3)The relationship between the permeability coefficient and different pore sizes under uniaxial tensioning and laterally confined tensioning for geotextiles has been proposed.For woven geotextile and needle-punched filament-fiber nonwoven geotextiles,this paper proposes the relationship between geotextile pore size and permeability coefficient based on the parallel capillaries aggregaion model.The sum of the fourth power of each pore size increases linearly with the permeability coefficient increasing.The variations of geotextile permeability coefficients under uniaxial tensioning and laterally confined tensioning are measured respectively by vertical permeability test.The experimental permeability coefficients are compared to the sum of the fourth power of pore size O₉₅,O₅₀ and O₃₀,respectively.The experimental results are in good agreement with theoretical analysis.The PSD curves and characteristic pore sizes of the needle-punched filament-fiber nonwoven geotextiles have been measured by bubble point test.