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Title: An experimental study of compaction band evolution in an anisotropic sandstone
Author: Townend, Edward
ISNI:       0000 0004 2669 9251
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2007
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Diemelstadt sandstone is a quartz dominated material of about 23% porosity. It has been characterised as transversely isotropic about the pole to its bedding plane by measuring the anisotropy of pore-fabric using a magnetic susceptibility technique, and by measuring elastic wave velocities as a function of azimuth around orthogonal cores. These measurements indicate an average void-space shape approximating an oblate spheroid with an anisotropy of around 6%. Conventional triaxial experiments were then performed on samples of Diemelstadt sandstone cored in directions normal and parallel to the plane of isotropy (the bedding plane), under effective pressure conditions sufficient to traverse the brittle-ductile regime and to induce failure by the development of discrete compaction bands oriented in planes normal to the maximum compressive stress. Results show that samples deformed normal to bedding are consistently weaker in the compactive regime than the samples deformed parallel to bedding. This observation is consistent with further measurements which reveal that discrete compaction bands have a more pronounced impact on the evolution of permeability in samples deformed in the direction normal to the bedding plane. However, the permeability reduction in both orientations is dramatic, with the bulk permeability of Diemelstadt sandstone falling by up to four orders of magnitude. Acoustic emission locations show that the velocity of compaction band propagation is less than 0.1 mm s-1, and that the seismic b-value response to compaction band inception is consistent with a grain-scale deformation mechanism. Microstructural observations reveal a more tortuous compaction band trace in samples deformed parallel to bedding, which is consistent with greater strength observed in this direction. Our experimental data validate earlier theoretical predictions from spring network models which also point towards the influence of anisotropy on the morphology of compaction bands.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available