The grouting technique is an important method in underground engineering that prevents water seepage and reinforces fractured rock mass. In this research, ultrafine cement-based grouting material, including ultrafine cement (UC), ultrafine fly ash (UFA), polycarboxylate superplasticizer (SP), colloidal nanosilica (CNS), sodium sulfate solution (SS) and water, was developed. The flow time, viscosity, bleeding, setting time and uniaxial compressive strength of the UC-based slurry were measured by orthogonal experiments, and the optimal mix proportion of the UC-based slurry was obtained based on the Taguchi-Grey relational analysis method. Microstructure analysis of the UC-based slurry was conducted using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests. The results showed that the Bingham model could provide a satisfactory description of the rheological properties of the UC-based slurry. The addition of CNS and SS could promote the hydration of the UC-based slurry and improve the microstructure of the hardened slurry, thereby increasing the strength of the hardened slurry. The optimum ratio for the UC-based slurry was water/solid (W/S) ratio of 1.0, and the contents of UFA, SP, CNS and SS by mass of UC were 40%, 0.2%, 4% and 4%, respectively.

Seepage from the pores of sandstone exposed in deep mines is difficult to block by grouting. In this paper, the permeability evolution of four subcategories of sandstone with different pore structures under different confining pressures, pore water pressures and temperatures is analyzed by experiments. (1) With increasing confining pressure, the permeabilities of the four tested subcategories of sandstone all decrease, but at different rates and to different extents. (2) With increasing pore water pressure, the permeability of subcategory I₁, I₂ and II₁ sandstones increases linearly, while that of subcategory II₂ sandstone decreases following a power function under low confining pressures and tends to be stable under high confining pressures. (3) With increasing temperature, the permeabilities of the four sandstone subcategories decrease at different rates. (4) The orthogonal experimental results show that the confining pressure has the greatest influence on the permeability, followed by the water pressure and temperature. (5) The confining pressure, pore water pressure and temperature produce stress-strain in sandstone and thus change the sandstone pore structure and permeability. The permeability evolution of sandstones varies with pore structure. The findings of this study can inform the classified grouting of deep sandstone and optimize grouting parameters.