Water inrush is one of the most dangerous disasters in coal mining. Due to the large-scale mining and complicated hydrogeological conditions, thousands of deaths and huge economic losses have been caused by water inrush disasters in China. There are two main factors determining the occurrence of water inrush: water source and water-conducting pathway. Research on the formation mechanism of the water-conducting pathway is the main direction to prevent and control the water inrush, and the seepage mechanism of rock mass during the formation of the water-conducting pathway is the key for the research on the water inrush mechanism. This paper provides a state-of-the-art review of seepage mechanisms during water inrush from three aspects, i.e., mechanisms of stress-seepage coupling, flow regime transformation and rock erosion. Through numerical methods and experimental analysis, the evolution law of stress and seepage fields in the process of water inrush is fully studied; the fluid movement characteristics under different flow regimes are clearly summarized; the law of particle initiation and migration in the process of water inrush is explored, and the effect of rock erosion on hydraulic and mechanical properties of the rock media is also studied. Finally, some limitations of current research are analyzed, and the suggestions for future research on water inrush are proposed in this review.

Reinforcing the performances of cemented backfill materials to recycle gangue and tailings is crucial for the sustainable development of mineral resources and mining waste management. However, under practical constraints of low cost, high waste ratio, low carbon emission, and low binder consumption, solidifying upcycles of mining wastes with toxicity, porosity, and mollification to cemented backfill materials with superior properties are inherently contradictory and challenging. This study reported a waste-to-wealth pathway that improves cemented gangue backfill materials by cellulose nanofibers to recycle mining wastes and partially replace cement. Mechanical compression, X-ray diffraction, thermogravimetry, mercury intrusion porosimetry, scanning electron microscopy tests, fractal quantitative analyses of microstructures, and molecular dynamics simulations were carried out to reveal the action mechanism of TEMPO-modified cellulose nanofibers on cemented gangue backfill materials. The difference in the contribution of TEMPO-modified cellulose nanofibers and mechanical cellulose nanofibers to the strengths of cemented gangue backfill materials was analyzed. The results show a series of microscopic improvements of cellulose nanofibers on cemented gangue backfill materials, including regulating cemented gel polymerization, increasing hydration nucleation, inhibiting carbonization, densifying pore structure, enhancing Ca-O connections and H bonds, and preventing C-S–H fracture along interlayer water. Excessive cellulose nanofibers are also found to be harmful to this composite mainly by delaying hydration crystallization and increasing pores by entrapping air, while it still exhibits improvements in deformation resistance and energy absorption despite strength deterioration. The strength and energy absorption reinforcements of this cemented hybrid materials induced by cellulose nanofibers with optimal dosage can reach up to 30 ~ 50%.