Abstract: Focused on the tailings dam breaching caused by continuous rainfall，and based on the saturated-unsaturated seepage theory，the non-equilibrium continuous equation and the momentum equation of water-sand mixture a mathematical model is put forward to describe the tailings dam breaching due to slope failure.The model considers the impact on drainage flow process of tailings dam due to the change of seepage and stress field，as well as the variation of breach slope and bed.Meanwhile，the model is applied to simulate the dam breaching process of a tailings dam under continuous rainfall，and the calculated results show that continuous rainfall infiltration makes seepage line of the dam constantly rising，and then leads to dam slope failure；The stress condition of dam body deteriorates rapidly after the collapse of slope，and the shear failure of the remaining wedge may occur under the action of upstream loads，after that the overtopping failure occurs.

Key words: Tailings dam, Continuous rainfall, Slope instability, Overtopping failure, Numerical simulation