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Title: An experimental study of the compaction and creep behaviour of oolitic sands
Author: Stafford, Catherine Elizabeth
ISNI:       0000 0001 3476 6782
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 1999
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There have been numerous studies which have both experimentally investigated and mathematically modelled the mechanics controlling the deformation of a sediment. However, there have been relatively few studies which have systematically investigated the effects of pore fluid chemistry, stress magnitude and grain size, although these factors are known to influence both time-independent and time-dependent deformation. This study aims to provide a better understanding of the mechanical processes which control the compaction and creep behaviour of oolitic sands. A systematic study has been undertaken to investigate the roles of effective stress, pore fluid chemistry and the initial grain size distribution, on the rate and extent of compaction. This study investigates the time-independent compaction of sands by uniaxial K0 compression and undrained shear deformation experiments performed in a high pressure triaxial cell. Time-dependent behaviour is investigated by constant stress creep tests, performed in oedometric cells. Results show that the deformation characteristics of oolitic sand are most strongly influenced by the effective stress magnitude. Deformation behaviour during K0 compression, undrained shear and creep is significantly different at stresses above and below the critical pressure for grain crushing and this behaviour can be described in terms of the Critical State Model: Oolitic sands behave as an overconsolidated material with a 'dry of critical' stress/pore volume state. At high stresses, stress corrosion is thought to enhance grain fracturing and grain-to-grain crushing. Experimental and microstructural data indicate that this is further enhanced in the presence of aqueous fluids and with increased time. No grain size deformation trends are seen in the oolitic sands tested here. This is attributed to the bimodal porosity which influences the deformation characteristics: An intergranular porosity promotes increased deformation in larger grains. However, an intragranular porosity complicates any such trends as the magnitude of this microporosity is dependent on the shape and size of the aragonite crystals forming the ooids as well as the size of the individual ooids themselves.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Sedimentary; Grain fracturing; Stress; Porosity