Research on Cement-Free Grouting Material for Shield Tunneling in Water-Rich Karst Regions

With the increasing number of anti-seepage reinforcement projects and the continuous improvement of quality requirements, high-performance and green requirements have also been put forward for grouting materials. Traditional karst cave grouting mainly uses cement-based grouting materials, which not only have high carbon emissions but also do not comply with the sustainable development strategy with regard to being green, low-carbon, and environmentally friendly. A green grouting material made by mixing a slurry A and slurry B is proposed in this paper. The solid phase of slurry A is composed of stone powder and bentonite, for which an anti-washout admixture is necessary. Slurry B is a suspension of thickener (CMC or HPMC) and anhydrous ethanol. By mixing the two slurries evenly, the grouting material is obtained. Experiments were used to investigate the ideal ratios of stone powder, bentonite, and water in slurry A, and the ratio of thickener to anhydrous ethanol in slurry B, and to analyze the development and evolution of the apparent viscosity of slurry A and slurry B after mixing. This study revealed that the optimum ratio of stone powder and bentonite was 4:1, and the most reasonable water-solid ratio was 0.8:1.0. The optimum ratio of anhydrous ethanol to CMC or HPMC in slurry B was 5:1. Slurry B was added to slurry A at a rate of 5~10% to obtain the best grouting material properties. The proposed mixed grouting material would not disperse even in flowing water and could harden and consolidate quickly. The strength of the consolidation grouting body was close to that of wet soil, which can meet requirements for tunnel construction.