Tomographic imaging of rock defects and rock failure process

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Embargoed until 2017-01-31
Copyright: Cheng, Yan
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Abstract
The behaviour of rock mass is governed by the properties of both the rock material and discontinuities in the rock mass. Ability to track development of cracks when a rock structure is subjected to stress is an important goal in rock mechanics and engineering. This research project focused on detecting fracture and rock joints (defects) and visualizing the failure process of rocks using tomography techniques. Acoustic tomography and acoustic emission tomography techniques have been developed and applied concurrently to the study of rock defects detection and failure process visualization. A series of experiments were conducted using acoustic tomography technique. In order to ensure homogeneous properties, the test materials were prepared with a cement-based grout. The feasibility of this technique to detect defects was assessed. The influence of curing period of the grout on wave propagation and defects visualization was studied, as well as the effects of fracture width, inclination, infill materials and the number of sensors. Stresses were induced within rock under different loading conditions associated with Brazilian tensile and uniaxial compression tests using relatively isotropic specimens. The changes in the specimens resulting from the applied stress conditions were monitored by acoustic emission tomography technique. Acoustic emission (AE) events were used as sources for tomographic reconstruction and the entire loading and monitoring process could be continuously monitored, which is a factor not achievable using traditional tomography techniques. AE counts and source locations were used to determine the development of micro-cracks. Initial velocity surveys were able to detect intrinsic anisotropy attributed to the presence of pre-existing micro-cracks. Velocity changes were related to crack closure and opening according to the comparison between tomographic images and the analysed stress field within samples. Detailed micro-crack development was analysed for the Brazilian test. Uniaxial compression tests were conducted in transversely isotropic specimens while monitored by the acoustic emission tomography technique. Specimens with the anisotropy plane at three different dip angles were studied. AE counts, AE event locations and tomographic imaging of velocity improved the understanding of the failure process in transversely isotropic specimens than would not otherwise have been possible with simple stress-strain analysis.
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Author(s)
Cheng, Yan
Supervisor(s)
Mitra, Rudrajit
Hagan, Paul
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Publication Year
2014
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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