The disposal of coal mine solid waste has always been a challenge in the coal mining production process, and the research and development of low-cost and high-performance filling materials is a prerequisite for achieving large-scale disposal of coal mine solid waste. The effects of water–cement ratio, foaming agent dilution ratio, foam agent content, foam stabilizer content, and gypsum content on the mechanical properties, transportation characteristics, and microstructure of cement foam filling materials were studied by laboratory test methods. The optimal ratio of cement foam filling material for comprehensive performance was determined. On this basis, the mechanism of influence of fly ash content, gangue content, and gangue particle size on the mechanics, transportation characteristics, and microstructure of foam filling materials was further studied. The experimental results show that at fly ash contents below 30%, gangue content is less than 30%. The particle size of gangue is less than 0.6 mm, and the expansion ratio of coal mine solid waste foam filling material is about three times, which has good mechanical properties and transportation performance. The on-site test results show that the control effect of the surrounding rock in the goaf is good, achieving safe and efficient mining of the working face.

Intensive extraction in shallow coal seam groups poses a severe threat to regional hydrogeological stability. This study investigates the evolutionary laws of water-conducting fracture zone (WCFZ) height and phreatic level response at the Wanli No. 1 Mine. Although limited to a two-dimensional physical model and a single-case study, the research integrates field monitoring with similarity simulations to evaluate the efficacy of gangue grouting backfilling (GGB). The results reveal a significant superposition effect in dual-seam mining, where cumulative disturbances trigger the reactivation of upper-seam fractures, causing the WCFZ to penetrate the surface (170 m)—a phenomenon absent in single-seam mining. Scientifically, this work identifies a dual-threshold effect for ecological and structural preservation. While an equivalent filling rate (η) of 35% is sufficient to maintain the ecological water level in single-seam mining, dual-seam extraction requires a minimum η of 65% to restrict phreatic drawdown within the 1.5 m ecological threshold. Notably, while the laboratory model suggests a higher mechanical safety limit of η = 80% to prevent fracture propagation, the 65% threshold provides a balance between backfilling efficiency and environmental protection. The primary scientific contribution of this study is the quantification of the coupling relationship between overburden mechanical stability and long-term ecological functions. By shifting the overburden failure mode from “surface-penetrating fracturing” to “controlled bending subsidence,” this research provides a robust theoretical foundation for decoupling mining intensity from hydrogeological degradation in fragile multi-seam environments.