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One type of seepage water that is difficult to plug by grouting is the water exuding through the pores of sandstone in deep underground engineering. Aiming at this problem, this paper collected deep-mine sandstone samples from the Southwest Shandong coalfield, studied the sandstone pore structure and its influential factors by casting thin slices, scanning electron microscopy, mercury intrusion and physical property tests, and selected five representative permeability classification indicators: permeability, porosity, average pore throat radius, comprehensive diagenetic coefficient and sorting coefficient. According to these five indicators, the pore permeability of all the sandstone samples was divided into four subcategories (I1, I2, II1, and II2) from the perspective of grouting. I1 has medium pores and medium pore throats that can be filled with ultrafine cement-based slurries; I2 has medium-small pores and fine pore throats; II1 has medium-small pores and fine pore throats or small pores and microthroats; both I2 and II1 can be filled with chemical slurries; and II2 has micropores and microthroats that cannot be grouted. This case study provides a reference for the classification and evaluation of the pore permeability of sandstone for grouting and lays a foundation for classified permeation grouting and subsequent pore-expanding permeation grouting. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The groundwater in nonkarst areas can be divided into two categories: pore water and fracture water. Unlike fracture seepage, sandstone pore seepage in deep mines manifests as a large area of "sweating," rather than an area of local "spray," and is difficult to plug via conventional grouting methods. This study focused on pore seepage in deep mine sandstone to improve the grouting effect. Taking the deep mine sandstone in the southwest Shandong coal field, where "large-area sweating" seepage occurs, as the study object, this study examined the pore structure, petrological characteristics, physical properties, and grain sizes of the sandstone by analyzing experimental data from thin sections and scanning electron microscopy samples. The formation mechanism of the "large-area sweating" seepage was then analyzed. The range of permeability in which "large-area sweating" seepage may occur in the sandstone was discussed. The results indicate that the process of "large-area sweating" seepage in deep mine sandstone can be divided into a matrix softening stage, a matrix erosion stage, and a "large-area sweating" water seepage formation stage. According to the case analysis on the "large-area sweating" seepage in the Tangkou coal mine of the Southwest Shandong coalfield, the lower limit of permeability of the "large-area sweating" sandstone is approximately 0.25 mD. Thus, this type of seepage can occur in deep mine sandstone with a permeability of greater than 0.25 mD and affect typical mining production. The results of this study provide information about the formation mechanism of "large-area sweating" water seepage from sandstone pores and can theoretically inform the development of a new permeation grouting technique. [ABSTRACT FROM AUTHOR]

• Visualized fragmentation experiments were carried out by releasing molten lead into subcooled water under different experimental conditions. • Parameter effects on the fragmentation process and debris properties are investigated in detail. • The dominant factors influencing the fragment sphericity and debris porosity are the thermal parameters, namely melt temperature and water subcooling. • Maps of the fragment sphericity and debris porosity are established based on the experimental results. In the present work, to investigate the thermo-hydraulic characteristics of molten lead jet fragmentation in water, visualized fragmentation experiments are carried out by releasing superheated molten lead into subcooled water at different experimental conditions using the VTMCI (Visualized Thermo-hydraulic characteristics in Melt-Coolant Interaction) facility at Sun Yat-Sen University. The parameter effects, such as melt temperature, water subcooling, boiling mode, penetration velocity and water depth, on the fragmentation process and debris properties are analyzed in detail. It is found that the dominant factors influencing the fragment sphericity and debris porosity are the thermal parameters, namely melt temperature and water subcooling. Based on the experimental results, the maps of the fragment sphericity and debris porosity are established. [ABSTRACT FROM AUTHOR]