Under water-rich geological conditions, tunnel engineering is highly prone to water leakage, which poses serious threats to construction and operational safety and has adverse environmental impacts. In this study, a novel permeable crystalline grout material (PCGM) was developed using a combination of a cementitious crystalline capillary waterproofing material (CCCW, XYPEX) and nano-SiO 2 (NS) for synchronous grouting in tunneling. Through systematic testing of both slurry and consolidated body properties, the effects of water-to-cement (W/C) ratio, XYPEX content, NS content, and polycarboxylate superplasticizer (PCS) content on the density, viscosity, setting time, bleeding rate, stone content, mechanical strength, and permeability of PCGM were investigated. Additionally, the microstructure, hydration products, and pore structure evolution of the PCGM underwent analysis. The results demonstrated that the synergistic incorporation of CCCW and NS effectively improved the basic properties of the slurry and enhanced the mechanical properties and impermeability of the consolidated bodies. Across mix designs, the stone content of the PCGM reached 100%, and the setting time was reduced markedly. The NS content played a dominant role in the initial stage of mechanical and permeability performance, whereas the XYPEX controlled the 28-d performance. Multi-objective optimization determined the optimal mix proportions of PCGM to be W/C ratio = 0.4, 3 wt% XYPEX, 1 wt% NS, and 0.3 wt% PCS. The catalytic-complexation-precipitation mechanism of XYPEX and the nano-filling effect of NS synergistically refined the pore structure of PCGM. These findings could provide a scientific basis for the application of green, high-performance impermeable grouting in tunnel engineering under water-rich conditions.
Zhang et al. (Sun,) studied this question.