A multi-scale assessment of the flow mechanics of polymer support fluids in granular soils

Polymer fluids present a number of advantages over bentonite-based alternatives for excavation support. Much is still to be learned about the permeation of these non-Newtonian fluids in soils and especially more permeable soils and there is uncertainty around the support forces imparted to the soil. This study develops a numerical framework based on a pore-network modeling approach to quantify the grain drag forces induced by polymer flows in sand packings. The model captures the shear-thinning rheology of polymer fluids and the emergent data reveal the distinct flow dynamics and their influence on grain-scale interactions. The shear-thinning rheology of these fluids amplifies flow heterogeneity, leading to a non-linear relationship between individual grain drag and the total applied pressure gradient if it exceeds a critical threshold. Implications of these fundamental observations for engineering practice are demonstrated through an example application to excavation support during diaphragm wall construction.