Physical and numerical models of pressure during waterproofing injections with polymer into concrete fractures

ABSTRACT Polymer injections in concrete fractures are commonly used for the waterproofing of tunnels. The pressure during the injection needs to be high enough to ensure polymer penetrability. This paper introduces two physical models for the study of the pressure inside concrete fractures during polymer injections. The injection parameters that were varied include pressure, injection duration, injection volume, location of the injection and pressure reading ports, and fluid dynamic viscosity. Water and water-glycerol mixtures were used to verify the influence of viscosity on flow. Tests were performed with both open and sealed fractures. The pressure inside the fracture during the injection was influenced by the dynamic viscosity, boundary conditions and the saturation level of the fracture. Sealed and initially moist fractures led to a higher pressure gain inside the fracture after achieving saturation. More than 40% of the injection pressure was already lost when the liquid entered the model. A numerical model of liquid flow in the fracture plane was developed with the finite element code COMSOL Multiphysics. It was able to replicate the influence of boundary conditions and initial fracture saturation on pressure. The model also shows how aperture and roughness influence the flow conditions in the fracture.