Abstract: In order to maintain the stability of the superlarge goaf and maximize the recovery of the pillar of a mine,by using engineering analogy method and theoretical calculation method,it is concluded that the design strength of 2 MPa and 1.5 MPa.According to the designed strength,the ashsand ratio is between （1∶4）～（1∶8）,after the stress analysis on both sides of the backfill,the ashsand ratio should be appropriately increased at the roof and floor with large stress,so that the compressive strength of the designed backfill is higher than the actual strength.Empirical formula and Yangxin formula are used to calculate and compare the selfsupporting strength of backfill,and the design strength of 40 m high backfill is 1.664 MPa.The study results show that the floor of No.3 ore body goaf is filled by cement with a sandlime ratio of 1∶4,and then it gradually drops to a sandlime ratio of 1∶8;in the middle section,the ashsand ratio is 1:4 and the filling height is not less than 6 m;in the roof 2 ~ 3 m,a higher ashsand ratio or even cement mortar should be used.Therefore,the best filling effects can be obtained,safety and sustainability production of the mine can be guaranteed.

Key words: Goaf,Full tailings cemented filling,Cementsand ratio,Selfreliance strength