[Objective]In order to study the effect of gradation on the dynamic shear behavior of coarse-grained soil-geogrid inter-face,[Methods]18 groups of different gradation samples were prepared by changing the maximum particle size(dmax)and gra-dation area(S)of the samples based on the continuous gradation equation,the cyclic direct shear tests with and without geogrids were carried out for each group of specimens,and the effects of dmax and S on the cyclic shear properties of interface were ana-lyzed,the shear stiffness coefficient αK and the damping ratio coefficient αD are introduced to evaluate the effect of geogrids on dynamic shear strength parameters.[Results]The experimental result show that the shear stiffness K increases with the increase of dmax,and the damping ratio D decreases with the increase of dmax.Conversely,the opposite trend is observed.K and D are logarithmically related to dmax.The relations of K/D with S can be expressed by quadratic polynomials.In addition,the relation-ship between αK/αD and aperture ratio is given,that is,with the increase of aperture ratio,αK increases first and then decreases,and αD decreases first and then increases.When the aperture ratio is about 0.073,the geogrid has the best reinforce-ment effect on the cyclic shear behavior of coarse-grained soil.[Conclusion]The result show that the interlock mechanism be-tween particles and geogrids has an important effect on the cyclic shear behavior of the coarse-grained soil-geogrid interface.When the particle size of most particles is smaller than the size of the grid,the interlock mechanism between particles and the grid is brought into full play.When the maximum particle size and the grid size are the same,there is an optimal gradation area,which makes the coarse-grained soil-grid interface have the best seismic performance.
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