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Abstract The infiltration angle of the soil/filter interface is deflected with nonhomogeneous anisotropic seepage filed and fluid regime in dyke-dams so as to bring about the local hydraulic factors mutation when the interface infiltration angle is nonorthogonal. In this paper，a multi-function seepage piping instrument was developed to carry out contact erosion tests. The test samples of the fill and filter material were taken from the site of the earth dam construction，and they were prepared at the angles of 30°，45°，60° and 90° between the seepage flow and the interface. It was conducted to investigate the mechanism of contact erosion by measuring the hydraulic interface factors under different hydraulic gradients in the laboratory. At the same time，a PFC3D numerical model was established by using the CFD-DEM method. The micro properties of internal erosion at the contact interface of soil/filter were simulated and analyzed by comparing with the experimental data according to the experimental facility?s working conditions. The results show that the seepage infiltration angle at the soil/filter interface has a significant impact on the effect of filtration. The indicators of the filter are better when the infiltration flow is orthogonal to the interface. However，the hydraulic factors comprising the infiltration flow velocity，the local hydraulic gradient，the pore pressure and the soil pressure have obvious variations due to the seepage flow refraction when the interface infiltration angle decreases. The fast seepage velocity aggravates the internal contact erosion and causes an accumulation more in the number of fine particles from the protected soil at the local interface，which weakens the filter efficiency of the filtering layer. It should be pointed out that both the experiment and numerical simulation reveal that the filter specimens still keep the function under a high hydraulic gradient，indicating that the current filter criterion has enough safety reserve.
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