Evaluation of rheology and washout resistance of cement-based grouts in water-rich strata

Abstract

The grout in water-rich strata is at risk of being washed away. To investigate its retention capacity during the washout process, rheological parameters characterizing the mechanical properties of the grout were tested. Additionally, a comparative analysis was conducted on the prediction accuracy of different rheological models for cement-based grouts, and a recommended prediction model for the rheological parameters was provided. By combining a CFD numerical model, the process of grout being washed out in the stratum was analyzed. The study results indicate that the Bingham model is the most suitable for regression analysis of rheological parameters in cement-based grouts. In the static washout process, reducing Water/Binder and Binder/Sand while increasing Bentonite/Water improves the resistance of grout to washout, with Cement/Fly Ash having a relatively smaller impact. During dynamic washout, Binder/Sand either above or below 0.65 result in higher grout washout resistance. Additionally, grouting increases grout volume in the stratum, with the retention rate being minimally influenced by grouting pressure. The static washout effect showed an excellent correlation with plastic viscosity, while the dynamic washout effect was more significantly related to yield stress. When shear stress exceeds 3.5 and plastic viscosity exceeds 0.6, the influence of rheological parameters on grouting effectiveness and retention capacity becomes negligible. Considering the grouting process, retention rate and diffusion capacity, three reference ratios were proposed for different application needs.