Experimental Study and Development of an Injection Grout Mix Proportioning Tool Based on Key Fresh-State Properties

Abstract

Injection grouting is widely used in underground construction to control groundwater inflow and improve rock mass stability. Despite its extensive practical application, grout mix design remains largely based on empirical experience rather than systematic, performance-based methodologies. This study investigated the relationships between grout composition and key fresh-state properties of cement-based injection grouts and developed a performance-based grout mix proportioning tool for practical applications. An extensive experimental program was conducted using two micro cement types combined with different water–cement ratios, accelerator systems, and superplasticizer systems. Rheological properties, including yield stress and plastic viscosity, were evaluated using the Bingham model at 5 and 20 minutes after mixing. Additional fresh state properties such as water separation, filtration performance, density, air content, and setting behavior were also assessed. The results demonstrated that the water cement ratio primarily governs the overall rheological level of the grout, while admixture type and dosage strongly influence early-age structuration, stability, and injectability. Certain grout combinations exhibited rapid stiffening and loss of pumpability, whereas others showed excessively low yield stress and increased segregation tendency. Filtration performance was also found to be closely linked to grout stability and particle interaction. Based on the experimental findings, a data driven injection grout proportioning tool was developed to assist in the selection and optimization of injection grout mixtures according to target fresh-state performance criteria. The proposed approach contributes to a more systematic and practical methodology for injection grout design and has the potential to support improved efficiency, stability, and quality control in underground grouting operations.