Geotubes are heterogeneous structures composed of filling sand and bag material, and its permeability characteristics are different from that of filling sand. The uncertainty of geotubes permeability characteristics results in the failure of seepage analysis of geotube dams, which restricts the safety assessment of the dams. As the basis of the study on the seepage mechanism of the geotubes, the influence of particle grading on permeability coefficient of filling sand and sand covered with

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... xtiles were explored by the permeability tests of filling sand with different particle grading under the condition of sand covered with or without geotextiles. And the influence of geotextiles on the permeability coefficient was analyzed by comparing permeability coefficient of sand covered with and without geotextiles. The test results show that the influence of single particle size content on permeability coefficient is consistent under the condition of sand covered with and without geotextiles. The content of powder, fine, medium and coarse particles is linearly related to their respective permeability coefficients. And the content of powder, fine, medium particles is negatively correlated with their permeability coefficients, while the content of coarse particles is positively correlated with the permeability coefficient. But the permeability coefficient of sand covered with geotextiles is smaller than that of filling sand under the same conditions. Finally, the parameter d 2 50 C c C u was selected as a variable representing the particle grading to fit the empirical formula of permeability coefficient of filling sand and sand covered with geotextiles.