Failure analysis of the 'backfill column - Immediate roof' cooperative bearing structure in constructional backfill coal mining.

The present article introduces a method called Constructional Backfill Coal Mining (CBCM) for the purpose of minimizing the expenses of backfill mining and making use of the subterranean space in coal mines. Investigations are made on the failure properties of the cooperative bearing structure, which consists of a backfill column-immediate roof in CBCM. For the analysis of the fracturing characteristics of the immediate roof, a mechanical model of the thick circular plate on elastic foundation is developed. Furthermore, numerical simulation experiments have been carried out to study the manifestations for failure of backfill columns. In the case study of Xinyang Mine, the findings reveal that the critical spacing of CBCM with a broken immediate roof, which contains a backfill rate of 20 % and a backfill column strength of 20.36 MPa, is 2.58 m. The direct roof is prone to tensile fracture when the backfill spacing exceeds 3 m. When the aspect ratio of the backfill columns is large, stress concentration occurs at the top and the underside corners of the column, resulting in the constitution of an elastic core in the middle of the backfill column. The critical aspect ratio for the formation of elastic core in backfill columns obtained from experiments is 0.8. This research can contribute to the application and promotion of CBCM in coal mining while it serves as a theoretical basis.