Permeability evolution and microstructural regulation of clay cement grouted body under coupled seepage and stress conditions

Clay-cement grouted body (CCGB), as a green grouting material, have been widely applied in mine grouting water-blocking technology, and their permeability characteristics are of great significance to the safe mining of mines. Based on this, in this study, CCGB specimens with different cement contents (50%, 70%, 90%) were prepared. Using a rock permeability test system, seepage-stress coupling permeability tests on CCGB were conducted under different cement contents, osmotic pressures, and confining pressures. The permeability characteristics evolution laws of CCGB under different cement contents, osmotic pressures, and confining pressures were clarified; combined with rock microscopic testing, the correlation characteristics among permeability, flow velocity, and porosity of CCGB under different cement contents, osmotic pressures, and confining pressures were investigated; and the permeability characteristics evolution mechanism of CCGB under seepage-stress coupling was revealed. The research results show that: (1) The permeability and microscopic pore structure of CCGB are significantly regulated by cement content: Increasing the cement content from 50 to 70% resulted in a decrease in permeability by 1.81 × 10−4 µm2 and a reduction in porosity by 0.076. Increasing the cement content from 70 to 90% resulted in a decrease in permeability by 2.538 × 10−4 µm2 and a reduction in porosity by 0.006; (2) Under seepage-stress coupling, the permeability of CCGB is affected by osmotic pressure through the enhancement of seepage erosion: as osmotic pressure increases, fluid erosion is intensified, and porosity, flow velocity, and permeability all increase; (3) Under seepage-stress coupling, seepage in CCGB is inhibited by confining pressure through the enhancement of volume compression: with the increase of confining pressure, the volume shrinkage and seepage inhibition effects of CCGB are strengthened, and porosity, seepage velocity, and permeability all decrease; (4) Under seepage-stress coupling, the permeability characteristics evolution of CCGB is dominated by the competitive balance between erosion effect and compaction effect, and microscopic pore structure and mineral composition are the key regulatory factors. The research results can provide theoretical guidance for the production practice of green grouting engineering.