This paper proposes a new montmorillonite-type multiple network composite gel for the prevention of coal spontaneous combustion. The first network is formed by the cross-linking of polyvinyl alcohol (PVA) and boric acid under alkaline conditions. The second network is formed as a result of intermolecular hydrogen-bonding interactions between polyacrylamide (PAM) and polyvinyl alcohol. Montmorillonite (MMT) is designed as the backbone material in the preparation of composite gels. The optimal ratios of the reactants of the composite gel were determined through orthogonal experiments. The experimental results showed that PVA had the greatest influence on the gelation time, whereas the PAM concentration had the strongest influence on the gel permeability. The optimal blending ratio was 4% MMT + 2.5% PVA + 1.5% PAM. The chemical performances of the composite colloids, such as inhibition rate, reactive functional groups, and kinetics, were investigated. Results showed that multiple network composite gels could effectively inhibit the coal spontaneous combustion reaction. Based on the principle of coal spontaneous combustion and the cross-linking network structure of the composite gel, the flame-retardant and fire-extinguishing mechanisms were also explored in terms of both physical and chemical inhibition pathways.

This paper is based on the condition where layered argillaceous cemented sandstone as an engineering background is met by the No. 207 fully mechanized working face open-off cut (Wanli No. 1 Coal Mine). Through mechanical theory analysis and field practice, the engineering safety problem of the large-span argillaceous cemented sandstone layered open-off cut roof supporting structure was analyzed. The roof caving arch height of the open-off cut roadway in 207 working face was obtained based on the mechanical mechanism of instability and caving of the layered surrounding rock mass roof. The anchor cable suspension and bearing stability of the open-off cut roof were analyzed in terms of the layered beam structure model. Meanwhile, combining with conditions, reasonable and effective support countermeasures and key parameters are proposed for such open-off cut roadway and enhance the actual supporting engineering on-site. These research results could provide engineering reference for an open-off cut roadway with composite roof conditions featured to weak cementation and weak interlayer.

Water inrush is the biggest threat for safe mining in the Ruifeng coalmine, located in North China. In the study mining area, the floor water inrush is mainly caused by mining activities and collapse column. In this article, the mechanical criteria of floor water inrush are obtained based on cusp catastrophe theory, which is used to assess floor water inrush risk in the Ruifeng coalmine. Theoretical analysis shows that floor water inrush is very likely to occur during coal mining without the influence of geological structures. Additionally, FLAC3D was used to simulate the damage of floor strata during the mining face advances. Numerical results show that the water inrush channel occurs in front of the mining face due to the influence of stress concentration. Therefore, a microseismic monitoring system was applied to monitor the formation of water inrush pathway. Field monitoring results show that two water inrush pathways were accurately predicted and positioned. Based on the microseismic monitoring results, target grouting was adopted to prevent water inrush. This study provides significant guidance for the prevention of floor water inrush.