Grouting effects on permeability of fractured rock masses: Experimental findings and implications for seepage control

Effective seepage control in fractured rock masses is critical for underground engineering safety. This study investigated the permeability evolution of fractured granite before and after cement grouting, considering the effects of grout water-to-cement (W/C) ratio, fracture roughness, fracture inclination, confining pressure, and seepage pressure. A total of 25 specimen series, including fractured granite, cement paste, and rock-grout composites, were tested, yielding 225 permeability measurements. The results show that cement grouting reduced the permeability of fractured granite by approximately three orders of magnitude under the tested conditions, demonstrating its effectiveness in blocking fracture-controlled seepage pathways. The W/C ratio was the primary factor governing sealing performance: the 1:3 composites exhibited the lowest permeability, whereas the permeability increased by 25%-48% for the 1:2 composites and by a further 30%-35% for the 7:10 composites, mainly due to enhanced capillary-pore connectivity at higher W/C ratios. The rock-grout composites remained less permeable than fractured granite but more permeable than cement paste, indicating that residual interfacial gaps, shrinkage-induced microcracks, and local filling defects acted as preferential seepage paths. Unlike the fractured granite and cement paste, the composites exhibited an inverse permeability-seepage pressure response, attributed to particle migration and clogging, constrained cement paste deformation, and narrowing of interfacial channels. Fracture geometry further regulated permeability by altering rock-grout contact, flow-path tortuosity, particle retention, and effective seepage length. These findings suggest that the permeability of grouted fractured rock is jointly governed by grout matrix properties, interface integrity, and fracture geometry, providing guidance for grouting-based seepage control in fractured rock masses.