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The apparent opening size (O95) of geotextile is a physical parameter closely related to the permeability property and/or amount of clogging of geotextile. In this paper, the various methods for apparent opening size of geotextile are discussed. The apparent opening size tests of geotextile on the wet and hydrodynamic method were performed, and the apparent opening size of each test method was evaluated. Based on test results, an improvement of each test method was proposed. It was found that the value of apparent opening size of geotextile obtained from wet and hydrodynamic methods were near to a theory value proposed by J.P. Giroud.

The apparent opening size (O95) of geotextile is a physical parameter closely related to the permeability property and/or amount of clogging of geotextile. In this study, since the apparent opening size is an important parameter, the apparent opening size test of geotextile on the wet method was performed and verified the adequacy of that test method. The apparent opening size of geotextile obtained from that test is discussed. Based on a series of constant head permeability test results on the various geomaterials carried out in the past, the effect of the apparent opening size on the permeability of the geotextile is also discussed.

A series of constant head permeability test was performed by putting in a geotextile between a geomaterial layer and a gravel layer in order to evaluate an effect of geomaterial on the cross-plane flow performance of geotextile filter. As the geomaterials for this study, Ataka loam, Kanto loam, Rokunohe sand with fine-grained and Muroran sand with fine-grained were prepared. Based on test results, it was found that the cross-plane flow performance of geotextile depended on the relationship between an amount of clogging per unit volume on each geotextile and a percentage passing by mass of soil particle size less than an opening size of geotextile. It is expected that a clogging mass and an amount of clogging per unit volume are affected by a fiber structure of geotextile.