Method determination on key position of coal mine constructional backfill based on fracture characteristics of roof structure

Backfilling mining is important for controlling strata movement and reducing surface subsidence and environmental damage. Insufficient sources of raw materials and high backfilling costs have become major bottlenecks, limiting the application of backfill mining in underground coal mines. Exploring new methods and supporting technologies of targeted backfill with low backfilling rate in key areas is one of the research hotspots in backfilling mining. To solve these problems, combined with the academic thought of constructional backfill in underground coal mines, an in-depth study of the fracture characteristics of roof strata is conducted, the hinged shape and size of broken blocks in the roof strata are clarified, the main subsidence area and position of broken hinged blocks are identified, and the key position of the constructional backfill is determined accordingly. Through the key position determination method, an “I-shaped” constructional backfill new scheme that focuses on controlling the maximum deflection position of the main roof, i.e., the potential tensile fracture position (plastic hinge development position) of the plate structure, is proposed. Combined with the geological parameters of the rock strata of Xinyang Mine, FLAC^3D numerical simulation software was used to analyze the stress, vertical subsidence, plastic zone distribution of the roof in the direction of mining width and advancing direction of the working face, and the stability evolution characteristics of backfilling body under different schemes are revealed. The results show that the “I-shaped” backfill can reduce the immediate roof subsidence in the initial mining period by 33.47% compared with the caving mining on the basis of saving the backfilling amount, and there is only a difference of 2.3% with the full backfill. At the same time, the backfilling body at the key position can effectively response the stress concentration caused by the rotation and subsidence of the roof, maintain its stability, and realize the long-term support for the roof. After comprehensive analysis, the best backfilling scheme for the “I-shaped” constructional backfill in the first coal face of Xinyang Mine is 72 m in length and 7 m in width in the middle strip, and 18 m in length and 6 m in width in the two side strips. Compared with full backfill, the cost of backfilling materials can be reduced by 0.338 6 million yuan. The scheme creates a confined space of 1980 m³, or 44% of the total mining space, which can be used for CO₂ or carbonized material sequestration, helping to achieve zero-carbon green mining and promote dual-carbon goals.