Establishment of the mechanical and hydraulic apertures of concrete fractures using 3D scans and hydraulic tests

ABSTRACT: Water infiltration through concrete fractures in tunnels causes deteriorations such as rebar corrosion. Chemical grout can be injected to seal concrete fractures. The fracture aperture needs to be considered when planning the injection because it affects the hydraulic characteristics of fracture such as the hydraulic conductivity. Two types of apertures can be defined: mechanical and hydraulic apertures. The mechanical aperture is the average distance between the two bounding surfaces of the fracture. The hydraulic aperture governs the liquid propagation and the head loss during the injection. This article presents four methods to establish both apertures. For the mechanical aperture, the physical model of a concrete fracture was built and scanned using the Polyworks software. The second method consisted of X-ray computed tomography (CT scans) on core samples taken from tunnels of the Montréal Métro. For the hydraulic aperture, an in-situ test was developed based on the injection of water-glycerol mixtures. A variable-head permeability test was also developed to establish the hydraulic aperture.