Fluid flow tests for a non- and dislocated rock fracture of Kuru granite and its replicas
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School of Engineering |
Master's thesis
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en
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75
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Abstract
Discontinuities in fractured rock mass, such as joints, faults, and bedding planes, significantly influence fluid flow in geological environments. Understanding fluid flow through these discontinuities is important for the safe disposal of nuclear waste due to fracture-controlled flow, which has the potential to transport radionuclides into the surrounding ecosystem. This study measures how fracture dislocation impacts fluid flow behaviour in rough, fractured rock, aiming to enhance our understanding of transverse fluid flow through dislocated rock joints for more reliable predictions of fluid movement around nuclear waste repositories. A 6 cm x 6 cm x 10 cm block of Kuru granite sample with induced tensile fracture was used for this study. High-resolution photogrammetry was employed to capture the aperture geometry of both well-matched and dislocated fracture surfaces. Then, the 3D models for the top and bottom surfaces of the physical aperture for the well-matched and each dislocation were created and measured using cloud-to-cloud distances in CloudCompare software, revealing a nonlinear increase in aperture with each fracture dislocation. Furthermore, those 3D models were developed and replicated using Fused Deposition Modelling (FDM) 3D printing. A custom-built fluid flow test apparatus was developed to measure fluid flow rates through non-dislocated and dislocated fractures under different water pressure levels. The effects on fluid flow behaviour due to non-dislocation and dislocation were experimentally examined and analysed using Forchheimer’s equation to calculate hydraulic aperture. Moreover, the results of the 3D printed replicas were compared with flow test results on the real rock sample to validate the accuracy of using replicas. Fluid flow tests on real rock, 3D printed replicas, and printed fracture apertures showed that increasing fracture dislocation leads to larger hydraulic apertures and higher flow rates, up to the maximum tested dislocation of 5 mm, following a nonlinear relationship with pressure gradient. Both the hydraulic aperture (eh) and the non-Darcy coefficient (β) are sensitive to the degree and direction of dislocation with the flow direction, confirming anisotropic fluid behaviour in the fractured rock and its 3D-printed models. Validation using 3D printed models demonstrated consistency in flow trends but highlighted differences due to surface and physical aperture reproduction limitations in 3D printing and photogrammetry.Description
Supervisor
Rinne, MikaelThesis advisor
Torkan, MasoudUotinen, Lauri