Experimental Study on Permeability Characteristics of Geotubes for Seepage Analysis on Safety Assessment of Dams

: Geotubes are heterogeneous structures composed of fi lling sand and bag material, and its permeability characteristics are different from that of fi lling 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 in fl uence of particle grading on permeability coef fi cient of fi lling sand and sand covered with geotextiles were explored by the permeability tests of fi lling sand with different particle grading under the condition of sand covered with or without geotextiles. And the in fl uence of geotextiles on the permeability coef fi cient was analyzed by comparing permeability coef fi cient of sand covered with and without geotextiles. The test results show that the in fl uence of single particle size content on permeability coef fi cient is consistent under the condition of sand covered with and without geotextiles. The content of powder, fi ne, medium and coarse particles is linearly related to their respective permeability coef fi cients. And the content of powder, fi ne, medium particles is negatively correlated with their permeability coef fi cients, while the content of coarse particles is positively correlated with the permeability coef fi cient. But the permeability coef fi cient of sand covered with geotextiles is smaller than that of fi lling sand under the same conditions. Finally, the parameter d 250 C c C u was selected as a variable representing the particle grading to fi t the empirical formula of permeability coef fi cient of fi lling sand and sand covered with geotextiles.