sSeepage tests on double-layer soils composed of sandy gravel and sand under different stresses and shear displacements

Many high embankment dams are directly located on the deep overburden layer. After the dam is constructed, large stress and shear displacement will appear in the dam foundation, which has great influence on the seepage stability of the overburden layer. Therefore, it is necessary to carry out the seepage tests on overburden layer considering the influence of stress and shear displacement. Using the large-scale high pressure permeameter, the seepage tests on the double-layer soil composed of sandy gravel and sand are conducted under different vertical stresses and shear displacements to investigate the variation of permeability and seepage resistance gradient with change in vertical and shear displacements. The occurrence and evolution of seepage failure are divided into stable seepage, transitional and failure stages. The test results show that the permeability of the double-layer soils decreases, while the initiated gradient of the fine particles and failure gradient of the soil samples increase with the increasing vertical stress. With the increase in shear displacement, the permeability decreases at first and then increases, while the failure gradient increases at first and then decreases rapidly. When there is no shear displacement and the shear displacement is small, the transitional period between the initiated gradient and the failure gradient is long. After large shear displacement occurs, the transitional period is greatly shortened, and the seepage failure occurs soon after the initiated gradient is reached.