Experimental Study on Cemented Filling of Granular Pile in Caving Goaf: A Case Study

For the metal deposits exploited by the open-stope subsequent filling method, the goaf roof is prone to large-scale caving when the stope ore is not fully mined. This further results in the accumulation of a thick layer of waste rock on the goaf floor due to the caving of surrounding rocks. In the treatment using cemented filling, it is essential to ensure that the filling slurry fully permeates into the granular pile, and that the granular-cemented backfill possesses sufficient strength to guarantee the production safety of adjacent stopes. Taking the caving goaf of Shirengou Iron Mine as the engineering background, the effects of slurry concentration, cement–tailing ratio, height of the granular pile, and particle size of the granular rock on seepage laws are investigated by means of a self-developed simplified filling test device. The filling slurry concentration that meets the on-site requirements for fluidity and permeability is thereby determined. Meanwhile, by prefabricating the granular-cemented backfill, the characteristics of the self-supporting capacity and strength of the backfill are studied, considering factors such as different slurry concentrations, cement–tailing ratios, and curing ages. The results indicate that the cement–tailing ratio exerts the least influence on the seepage law, yet it has the most significant impact on the strength of the granular-cemented backfill. When the cement–tailing ratio of the filling slurry ranges from 1:8 to 1:4 with a concentration of 68%, the filling slurry can completely seep and cement the waste rock layer. At this point, the granular-cemented backfill strength can reach 1~2 MPa, which satisfies the seepage and cementation requirements for the waste rock inside the caving goaf of Shirengou Iron Mine.