Microscale to macroscale bentonite grout flow in sand

Permeation grouting is a soil improvement technique that involves injecting a grout into the pores of a soil volume to enhance its engineering properties. Bentonite grouts are commonly used for seepage control, and their effectiveness in improving the resistance of sand to static and cyclic loading has been demonstrated. However; modeling bentonite grout flow has been challenging due to its complex rheology and the intricate nature of soil pores. Since grouts exhibit non-Newtonian rheological behavior, using Darcy law with a constant hydraulic conductivity cannot accurately describe grout flow in soil. In this paper, we propose a model that represents soil pores as idealized capillary tubes. This model derives the macroscale grout behavior in soil from the microscale grout behavior inside individual pores. It incorporates the grout’s power law rheological model and considers a nonzero slip boundary condition between the grout and the walls of the capillary tubes. To evaluate the model, a series of experiments was performed under different conditions. The proposed model offers a simple and robust method to predict the relationship between injection pressure and injection rate for power law grouts. It also highlights the importance of considering a nonzero slip boundary condition for bentonite grout injection.