Elsigood, Bobby;
(2023)
Measurements and modelling of anisotropic poroelasticity in rocks.
Doctoral thesis (Ph.D), UCL (University College London).
Preview |
Text
thesis_corrections.pdf - Accepted Version Download (15MB) | Preview |
Abstract
The poroelastic behaviour of cracked rocks is expected to depend on the geometry and properties of the crack network. Any preferred orientation of microcracks produces anisotropy in physical rock properties, including poroelastic parameters. This can be explored in the laboratory using a triaxial deformation apparatus. During triaxial loading there is an alignment of cracks parallel to the vertical direction of compression, leading to vertical transverse isotropy in the cracked rock. Firstly, attempts were made to validate a recent theoretical model (Wong, 2017) which showed that only two components of a crack density tensor can be used to determine poroelastic quantities of a rock. An experimental protocol was developed to test this theory by measuring anisotropic poroelastic parameters in a sample at increasing levels of differential stress (increasing stress-induced anisotropy). Axial and radial stress were rapidly cycled to induce an undrained poroelastic response. Pore pressure was measured in situ, directly on the sample surface, allowing for the axial and radial Skempton coefficients to be determined. In parallel, drained compliances were measured and the crack density tensors were estimated from measurements of ultrasonic wave velocities in the dry sample. This work was extended to measure how the strain and pore pressure change in response to rapid stress changes in an initially intact sample of granite which underwent increasing amplitude cyclic loading. Results show that the radial pore pressure build-up coefficient increases with increased differential stress, and the axial coefficient decreases and even becomes negative (where increases in axial stress cause a decrease in pore pressure) at high stress (i.e., about 80% of failure stress). During partial unloading, the measured coefficients show hysteresis, but following full unloading, the coefficients are observed to be recovered, without hysteresis.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Measurements and modelling of anisotropic poroelasticity in rocks |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10164549 |
Archive Staff Only
 |
View Item |
