Abstract: Suffusion is the main and prominent form of seepage stability in deep alluvium foundation. It is of great theoretical and practical significance to carry out relevant experiments and theoretical studies on suffusion in deep alluvium foundation for the safety of major hydropower projects under construction and to be built in China. In this paper, firstly, it is pointed out that the mechanisms of backward erosion piping and suffusion are completely different, so they cannot be confused together. Compared with backward erosion piping, suffusion is more subtle, and its mechanism is more complex. Secondly, the research of suffusion is summarized in detail from three aspects: geometric condition, hydraulic condition and mathematical model. Finally, combined with the lower Yarlung Tsangpo River hydropower development and other major national projects, the following aspects should be emphasized, including the evaluation of internal stability in deep alluvium foundation, the mechanism of suffusion initiation and progression under extreme conditions, complex seepage conditions and formation conditions, the evaluation and control of suffusion time effect and its long-term impact, and the experimental and theoretical research of suffusion constitutive relation and its mathematical model.

Key words: deep alluvium foundation, permeability stability, suffusion, backward erosion piping