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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 80
Edited by: B.H.V. Topping and C.A. Mota Soares
Paper 113

Obtaining the Geotextile Pore Size Distribution Curve using Image Analysis

D.C. Urashima and C.H. Martins

Institute for Research and Development, Vale do Paraíba University, São José dos Campos, Brazil

Full Bibliographic Reference for this paper
D.C. Urashima, C.H. Martins, "Obtaining the Geotextile Pore Size Distribution Curve using Image Analysis", in B.H.V. Topping, C.A. Mota Soares, (Editors), "Proceedings of the Fourth International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 113, 2004. doi:10.4203/ccp.80.113
Keywords: geotextile, filtration, pore size, filters, image analysis, geosynthetics.

Geotextiles have been used as filtering element throughout the world. This is one of their most important application. Particularly in environmental works they represents a versatile solution easily applied and controlled, providing a good performance.

The successful geotextile filter design can often be achieved by the consideration of the following criteria: retention, permeability, survivability and clogging resistance. However for the retention criteria it is necessary to know the filtration characteristics or pore size distribution.

Filtration characteristics and pore size distribution of geotextiles have been largely discussed in literature [1]. The usual methods to analyse the filtration parameters of geotextiles are based in different conception and generally they are not applicable to obtain the geotextile pore size distribution.

Different techniques have been developed to measure the geotextile pores size and frequency. The pore size distribution curve has been evaluated in the last years by theoretical evaluation or direct and indirect measurement methods.

The paper presents a proposition to evaluate the pore size distribution curve obtained by image analysis. It is a direct measure method based on new digital images processing techniques. This proposition permits he recognition and measurement of particular image attributes by mean of digital procedures.

Geotextile porometric structure images can be taken from pictures generated by a video camera connected to a microscope with 50 - 300 time magnifying capacity and examined in real time with a monitor plugged in a computer that allows to capture the image with a specific software.

To analyze the image attributes it is necessary to identify and separate the pores inside the filaments or fibers that compose the taken image of the geotextile. The pores are defined by the void spaces between the detected filaments or fibers. This pore delimitation is necessary to calculate the attributes to be analyzed in order to obtain the pore size distribution curve. The digital images are submitted to boundary detection and morphologic filters. Subsequently segmented in homogeneous regions to extract the chosen geometric attributes: area, major and minor axes of a inserted ellipse and roundness.

The geometric parameters chosen to obtain the pore size distribution curve are the diameter calculated from the minor axes, taken directly as a diameter.

The statistical procedure to evaluate the number of images to be analyzed for representative sampling of the universe should be considered. To estimate this number it should be first considered that the pore diameters are distributed alike a normal. From the T Student distribution with a defined significance is possible to verify if the number of taken images is sufficient to define a representative pore size distribution curve.

The use of the techniques of digital processing of images in the geotextile pore size distribution curve tends to be promising to analyse the filtration parameters of geotextiles

Christopher, B.R., Holtz, R.D.; Fischer G.D. "Research needs geotextile filter design", International Conference on Filtres and Filtration Phenomena in Geotechnical Engineering, Karlsrule, Germany, pp. 19-26, 1993.

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