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Title: Experimental studies of fault zone development in a porous sandstone
Author: Mair, Karen
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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This study investigates the processes involved in the formation and evolution of faulting in high porosity sandstone using laboratory triaxial compression testing. Faults in highly porous sandstone significantly affect the porosity and permeability of the rock, and typically occur as anastamosing compound bands of damage. Previously only the individual unit of these deformation band structures had been re-produced in the laboratory, possibly due to limitations on sample size. Now by deforming large specimens, I have not only produced zones of deformation bands, but also observed their hierarchical development as a function of strain - for the first time. A series of dry tests were carried out on initially intact 100mm diameter cores of Locharbriggs sandstone, at a constant confining pressure of 34.5MPa, a constant axial strain rate of 5x10E-6/s and increasing amounts of axial strain. Samples were driven over their failure curves and then subjected to differing amounts of post failure sliding. A second series of tests were carried out at increasing confining pressure (in the range of 13.8MPa to 55.2MPa) and constant amounts of axial strain. The response of the rock to the loading conditions was continuously monitored throughout the tests by recording the axial load, the axial strain and volumetric strain. Deformation structures and gouge material produced were studied by hand specimen, thin section and laser particle size analyses. The samples exhibited essentially brittle behaviour with small amounts of strain hardening and softening occurring near peak stress. Dynamic failure was accompanied by a measurable stress drop, which systematically decreased in magnitude as a function of confining pressure. Both compaction and dilatancy are observed in the volumetric strain curves. The amount of dilatancy decreased systematically with increasing confining pressure, until at high confining pressures, compactive behaviour dominated.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available