The influence of rock seepage must be considered in geotechnical engineering, and understanding the fluid flow in rock fractures is of great concern in the seepage effect investigation. This study is aimed at developing a model for inversion of rock fracture domains based on digital images and further study of non-Darcy flow. The visualization model of single rock fracture domain is realized by digital images, which is further used in flow numerical simulation. We further discuss the influence of fracture domain geometry on non-Darcy flow. The results show that it is feasible to study non-Darcy flow in rock fracture domains by inversion based on digital images. In addition, as the joint roughness coefficient (JRC) increases or the fracture aperture decreases, distortion of the fluid flow path increases, and the pressure gradient loss caused by the inertial force increases. Both coefficients of the Forchheimer equation decrease with increasing fracture aperture and increase with increasing JRC. Meanwhile, the critical Reynolds number tends to decrease when JRC increases or the fracture aperture decreases, indicating that the fluid tends to non-Darcy flow. This work provides a reference for the study of non-Darcy flow through rock fractures.

Damage to mine shafts located below thick loose aquifers, caused by coal seam mining, can seriously affect the operational safety of mines. In view of such a problem, the comprehensive weight method and the fuzzy matter-element analysis method were used to analyze and evaluate the stability of mine shafts below thick, loose aquifers. Based on data relating to shaft structure parameters collected from fifteen damaged shafts in coal mines in East China, a comprehensive analysis was performed. The results showed that (1) the two indexes of surface subsidence velocity and water level drop value at the bottom of a loose aquifer have a large influence on the stability of shafts below thick loose aquifers, and (2) the predicted results of thirteen sets of samples were the same as the results measured during actual production; the accuracy of the model was 86.67%. The comprehensive weight method and the fuzzy matter-element analysis model both show good reliability for evaluating the stability of mine shafts below thick loose aquifers and can provide a scientific reference for the analysis of the stability of mine shafts in areas with thick loose strata, as well as for the design of comprehensive control plans that could subsequently be implemented.

During coal mining, when loose water-bearing sand layers are exposed and connected, it is extremely easy to cause water and sand inrush accidents, threatening the lives and properties in mines. Because of the intricate and tortuous internal structure of the sand layer, the diffusion pattern of grouting slurry within the loose sand layer has not been accurately characterized. Improving the efficiency of grouting and reducing the cost of grouting are common difficulties faced by industrial and mining enterprises in the grouting renovation of loose water-bearing sand layers. This paper innovatively proposes the mechanism of slurry-water displacement effect based on the diffusion characteristics of grouting slurry within the water-bearing sand layer. It studies the power-law fluid seepage and diffusion mechanism of porous media tortuosity effect and slurry-water displacement effect and derives the spherical diffusion equation of power-law fluid seepage grouting considering the coupling of porous media tortuosity effect and slurry-water displacement effect. At the same time, an indoor experimental device considering the slurry-water displacement effect is designed to verify the rationality of the spherical seepage grouting diffusion equation considering the superimposed effects of the two. Furthermore, relying on the COMSOL Multiphysics platform, a three-dimensional numerical calculation model of the power-law fluid spherical seepage grouting mechanism considering the porous media tortuosity effect and slurry-water displacement effect is constructed. It analyzes the seepage and diffusion characteristics of power-law grouting slurry in water-bearing sand layers, and studies the influence of different porosity of loose water-bearing sand layers, spacing between slurry and water holes, grouting pressure, and slurry viscosity on the volume of loose water-bearing sand layers. The key factors affecting the volume of loose water-bearing sand layers are grouting pressure > spacing between slurry and water holes > porosity of sand layer > slurry viscosity. Compared with previous grouting technologies and processes, the slurry-water displacement grouting technology can solve the problems of small grouting diffusion range and poor grouting effect in high-pressure underwater water-bearing sand layers to a certain extent.