Replica-based experimental framework for characterizing fluid flow in a dislocated fracture

Summary

Abstract

Fractures significantly impact fluid flow in rock masses and comprehending how dislocations influence fracture-controlled flow is important for evaluating fluid movement in geological engineering applications, particularly for the long-term safety of geological nuclear waste disposal sites. In this method, A 6 cm × 6 cm × 10 cm Kuru granite specimen containing an induced tensile fracture was scanned using photogrammetry. Photogrammetry was used to capture the fracture surfaces and aperture geometries of the perfectly matched state and each dislocation step of the specimen’s upper half, using markers with known distances to accurately align and scale the dislocated surfaces. The 3D models of the upper and lower surfaces of the physical aperture were then modelled for each dislocation step and reproduced using Fused Deposition Modelling (FDM) 3D printing. The printed aperture models incorporated an inlet and outlet to allow fluid flow testing within a fully watertight assembly, enabling precise measurements through accurately replicated apertures. This configuration provided controlled experimental conditions and enhanced the reliability and precision of the flow data. A custom fluid-flow apparatus was developed to measure flow rates through the replicas at varying water pressures, enabling experimental examination of the effects of dislocation on fluid-flow behaviour. Further results were evaluated through the Forchheimer equation for hydraulic aperture calculation. The fluid flow tests revealed that increasing fracture dislocation results in higher flow rates, following a nonlinear relationship with the pressure gradient and leads to increased hydraulic apertures up to the tested limit of 5 mm dislocation. However, limitations related to the replication of fracture surfaces and physical apertures in 3D printing and photogrammetry must be assessed to ensure the accuracy of the results.