Yao Lu

Traditional underground backfill mining generally faces persistent bottlenecks such as insufficient filling material supply, high transportation costs and low filling efficiency. As an emerging green mining technology realizing in situ backfill material self-sufficiency, cut-and-fill mining provides an effective solution to the above problems, but the influence mechanism of its key geometric parameters on engineering performance remains unclear, restricting standardized parameter design and field promotion. Taking a shallow-buried coal mine in Ordos as the engineering background, this study carries out physical similarity simulation tests to systematically investigate the evolution laws of overburden displacement and stress distribution under three controlled scenarios: a baseline condition (4 m mining thickness, 10 m filling width), reduced mining thickness (2 m, 10 m), and increased filling width (2 m, 15 m). The results show that mining thickness acts as the dominant factor governing the strata control effect: when mining thickness is reduced from 4 m to 2 m, the maximum vertical displacement at the 10 m survey line decreases by 53.8%, the coal pillar stress concentration factor drops significantly, and the main roof maintains structural integrity without large-scale fracture. Increasing filling width enhances the bearing capacity of gangue pillars and restores filling zone stress closer to the in situ level, but tends to induce separation fractures in higher strata. Overall, the strata behavior of cut-and-fill mining presents distinct zoning characteristics, with high-position strata movement transitioning to coordinated integral deformation instead of severe separation and fracture. The findings provide an experimental basis and design reference for geometric-parameter optimization and engineering application of gangue backfill materials in underground mining.

To elucidate the influence of mineral composition on CO₂ mineralization and mechanical reinforcement, three synthetic tailing systems representing felsic, high-calcium silicate, and magnesium-carbonate compositions were prepared using a full-component reconstitution approach. Their carbonation kinetics, phase evolution, pore structure, and mechanical response were systematically investigated. The alkaline buffering duration increased in the order of felsic < high-calcium silicate < magnesium-carbonate types, with plateau durations of approximately 300, 650, and 2000 s, respectively. TG-DTG, XRD, and FTIR analyses collectively indicated composition-dependent formation of carbonate-bearing products, with the magnesium-carbonate type showing the strongest carbonate-related signals. SEM observations further revealed precipitation on particle surfaces and within interparticle regions, suggesting precipitation-induced particle bonding. Nitrogen adsorption–desorption measurements showed pronounced pore-structure reorganization after mineralization; the average pore size converged to approximately 7.5–7.9 nm, whereas the specific surface area decreased in all systems. The failure loads of the felsic and high-calcium silicate types increased by factors of 2.97 and 3.81, respectively. The mineralized magnesium-carbonate type exhibited the highest apparent compressive strength (53.69 kPa). These results demonstrate clear composition-dependent relationships among carbonation, pore evolution, and mechanical response in the synthetic systems. Because the materials were prepared from analytical-grade reagents and no complete carbon balance was established, the results should be regarded as mechanistic model-system evidence rather than quantitative estimates of CO₂ sequestration in natural tailings.

To address the problem of surface subsidence caused by the compression of filling gangue in deep mines, a layered compaction test was designed based on the zonation of the failure of the overburden in the goaf and layered property of the filling gangue. The deformation characteristics of filling gangue in natural and water-bearing states were obtained. The deformation of filling gangue during the 0~100 kN loading stage was an approximately positive S-type, which reflects the relative “advancement” in terms of deformation. The filling gangue deformation in the 100~500 kN loading stage was an approximately inverted S-type, which reflects the relative “lag” in terms of deformation. In a natural state, the load-time curves of the dead load stage were consistent. Under a water-bearing condition, the load-time curve for the dead load stage had apparent “step” characteristics and presented a special phenomenon of displacement rebound. Under gradient loading, the strain showed an exponential growth model, and energy dissipation showed a logarithmic growth model. Under a natural state, the energy dissipation showed consistently increasing distribution patterns, while the energy dissipation showed a normal distribution model under the water-bearing state.

After the previous exploitation of the coal resources below villages, a large number of Residual Strip Coal Pillars (RSCP) have been left. How to mine the RSCP without obvious secondary mining deformation on the surface has become a new direction of green mining at present. In this paper, Cemented Paste Backfill (CPB) is designed to replace mining RSCP. Considering the pumpability and strength, orthogonal test is conducted to comprehensively analyze the variation trend of different indexes under different factor levels, and a reasonable proportion is obtained to ensure the safety and rationality of mining. Through a self-designed dynamic paste filling device, the similar simulation contrast test is carried out, the characteristics of mining failure are obtained under the filling mining. Through field measurement, it is found that the compression of the filling body and the overall deformation of the roadway are relatively small, the velocity of roadway roof and floor movement slightly change. Finally, main influencing factors and the specific proportion of the roof deformation are obtained through field measurement analysis. This paper can provide the theoretical basis and practical experience for similar mining of RSCP.

Filling mining is an effective way to settle the dilemma of “Three Down and One Above” in coal mining. Fly ash and coal gangue can be used as filling materials with significant social, economic, and environmental benefits. Using coarse fly ash base as cementing material and coal gangue as aggregate, orthogonal experiment of filling paste was conducted in this study. The range analysis was performed for the strength and transportation requirements of filling paste, and the optimum proportion was determined by the comprehensive balance method. In order to verify the filling effect, a dynamic filling simulation device was designed, and a comparative simulation test of caving mining and dynamic filling mining was carried out. Results show that the filling paste with fly ash and coal gangue as the main component can meet the requirements of filling design and application. This research provides a reference for the material selection and proportion design of paste filling.

In order to research the influence of high-sulfate mine water on filling paste, the macroscopic and microstructural changes of the filling paste in the sulfate environment were analyzed by uniaxial compression tests, X-ray diffraction (XRD) and scanning electron microscope (SEM). The mechanism of deterioration and cracking was discussed. The experimental results show that there are numerous gelling materials in the specimen during the curing period, which can increase the strength of the specimen. After cured paste specimen was soaked in sulfate solution for less than 90 days, the hydration reaction continued, the gelling substance was produced and the sulfate formed the filling material, which caused the compressive strength of the paste specimen to increase with the increase of immersion age. The compressive strength of the specimen was higher than that of the specimen soaked in water. The gypsum and ettringite formed in the specimen filled the void of the specimen after immersion in sulfate solution for more than 90 days, destroying the original cementing structure of the specimen, and the compressive strength of the specimen began to decrease with the increase of the immersion age. The compressive strength of the cured paste specimen after being soaked in sulfate solution for more than 180 days was lower than that of the specimen soaked in clear water and the larger the solution concentration, the longer the immersion time, the smaller the compressive strength of the specimen, and the more significant the deterioration effect is.