Abstract: A series of tests are conducted on the engineering mechanical properties of sand slate rockfill materials for an ultra-high asphalt concrete core dam. It is found that with the increase of the porosity and slate content, the softening behavior of stress-strain curve weakens and the peak strength decreases. The volume change increases, and the shear dilation phenomenon fades during the shearing process. The linear strength indexes c and \varphi , the nonlinear strength indexes \varphi _0 and \Delta \varphi , and the Duncan model parameters K and K_b all decrease. The empirical formulas for the strength indexes and deformation parameters are proposed to predict the engineering mechanical properties of the sand slate rockfill materials with different slate contents and porosities precisely. It is also found that the permeability decreases with the increase of the slate content. The slate content is one important factor for the permeability performance of rockfill materials, and the drainage design of the rockfill area should be considered in the dam design.