Investigation On The Permeability Of Nonwoven Geotextiles

Non-woven geotextiles with excellent properties and low cost have attracted growing attention for the application in combating desertification,soil and water conservation.Vegetation Protection. water conservancy and so on.A good knowledge of permeability is required to an understanding of nonwoven geotextiles performance.The previous models contain empirical constants and involve only a few of structure characteristic parameters.In this research the basic fractal permeability model of nonwoven geotextiles based on Darcy's law and Hagen-Poiseulle equation was introduced.An analytical model is established in terms of well-defined structural parameters.Fibers in the non-woven geotextiles are randomly distributed to form a complex structure.For this reason,the pores thus formed have various shape and complicated pathways,resulting in an increased difficulty to characterize them by traditional geometry theory.Moreover,experimentally characterizing them is time-consuming and expensive,with permanently damage of the specimens. In this paper,the fractal theory is firstly introduced to theoretically characterize the pore size distribution in non-woven geotextiles.Based on fractal theory,the pore area fractal dimension D_f is determined by Sierpinski-basket method with Matlab to process SEM images of surface morphology.According to the binary images of surface morphology,computer simulation on tortuous capillary tube with Matlab was developed,and tortuosity fractal dimension D_T is determined by box-counting method.One advantages of this model is without any empirical constant.The fractal permeability model is in terms of the mass per unit areaμ_g,thickness T_g,fineness of the fiber N_dt, density of the fiberρ_f,cross section area A,pore area fractal dimension D_f,the tortuosity fractal dimension D_T.The other advantage is to simulate the tortuous capillary tube by computer based on the binary images of surface morphology and fractal theory.Comparison of theoretical values with experimental ones shows that a good agreement was observed.The fractal permeability model has no experience constant,so it is better than the Kozeny-Carman.Applying fractal theory in the non-woven geotextiles not only provides theoretical basis for the development of high-performance and high-quality non-woven geotextiles, but also explore new ways for nonwoven geotextiles research.