Abstract: To analyze fracture development laws of overlying strata by solid backfill mining, by considering the thin bedrock under thick alluvium as a bearing structure above the solid filling materials, the model of Winkler elastic foundation continuous beam for the single thin bedrock was built, and the relation between the compression modulus of filling body and the fracture development height of single thin bedrock was obtained by the mechanical analysis. In addition, the correspondence between the fracture development height of single thin bedrock and the filling percentage were established by analyzing the compression characteristics of solid filling material. Combined with practical work, the UDEC numerical model based on mechanical analysis was further built, and the fracture developments of rock beam were analyzed with the filling percentages of 60%, 70% and 85% in solid backfill mining. The results show that the strata fracture development height can be inhibited by solid backfill mining duo to the supporting effect of filling body to the overlying strata during coal exploitation. Meanwhile, the strata fracture development height increases rapidly after the coal face moving forwards about 30 m to 50 m, and decreases rapidly with the increase of filling percentage. Thus, the solid dense backfilling is a safe and effective method in coal mining under the thick alluvium and thin bedrock.

Key words: thin bedrock, backfill mining, filling percentage, fracture, mechanical model