Abstract: In order to calculate the critical hydraulic gradient of no cohesive soil during water seepage， numerical simulation on seepage experiments was conducted with PFC^3D. The numerical results agree well with the seepage experiments， thus verifying the effectiveness of PFC^3D model. Then， the damage during seepage of no cohesive soils with different particle friction coefficient was numerically simulated. The results showed that critical hydraulic gradient of no cohesive soil during water seepage increases with the raising of particle friction coefficient. The PFC^3D results agree well with the empirical results， and the effectiveness of calculation in seepage critical hydraulic gradient is validated. Compared to empirical formula， PFC^3D can be available for analyzing the seepage under complex engineering and geological conditions. It can provide a scientific reference and basis for seepage calculation under complex conditions.

Key words: no cohesive soil, seepage, critical hydraulic gradient, particle model, numerical simulation