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.

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.

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.