Abstract:Underground goaf use fine-grained tailings filling, fine-grained tailings tend to form a thin layer of fine mud on the surface of backfill, fine mud impermeable layer prevents the clarified water above the surface of the filling penetration down, affecting the quality of filling body. Backfilling materials by fine grain filling in the underground mine-out area and its filling body surface subsidence model study of the mechanism of fine clay impermeable layer. Through the experimental study, use of flocculants can inhibit the filling body surface formation of fine clay aquiclude. Different flocculants have different effect. From the consideration on the economy and the effect, choose alum as flocculant is more advantageous.