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Effect of subglacial shear on geomechanical properties of glaciated soils

dc.contributor.advisorSharma, Jitendraen_US
dc.contributor.committeeMemberPufahl, Dennis E.en_US
dc.contributor.committeeMemberElshorbagy, Amin A.en_US
dc.contributor.committeeMemberDolovich, Allan T.en_US
dc.contributor.committeeMemberBarbour, S. Leeen_US
dc.contributor.committeeMemberAntunes, Jorgeen_US
dc.creatorHuang, Bing Quanen_US
dc.date.accessioned2005-06-08T14:56:40Zen_US
dc.date.accessioned2013-01-04T04:36:47Z
dc.date.available2005-06-09T08:00:00Zen_US
dc.date.available2013-01-04T04:36:47Z
dc.date.created2005-06en_US
dc.date.issued2005-06-02en_US
dc.date.submittedJune 2005en_US
dc.description.abstractContinental glaciers covered as much as thirty percent of the present-day inhabited earth during the Quaternary period. Traditionally, one-dimensional consolidation has been considered as the main process of formation for the soils deposited during glaciation. One of the outcomes of accepting one-dimensional consolidation as the main process of formation is that the geomechanical properties of soil in a horizontal plane are isotropic (known as cross-anisotropy). Recent measurements of subglacial pore pressure and preconsolidation pressure profile have indicated that this might not be the case. The role of subglacial shear action has probably been long neglected. The main objective of this research is to investigate the effects of subglacial shearing on the geomechanical properties of glaciated soils. Recent research has found evidence of horizontal property anisotropy associated with the direction of the ice-sheet movement. A testing program was thus proposed to explore the relationship between the anisotropy of property and the direction of past glacier movement. The program involves several fundamental engineering parameters of soils. These parameters together with the corresponding test methods are as follows: (i) Conventional oedometer test – yield stress anisotropy; (ii) Oedometer test with lateral stress measurement – stiffness anisotropy; (iii) Load cell pressuremeter (LCPM) test – in situ stress anisotropy. The physical meaning of yield stress determined by conventional oedometer tests was interpreted as the critical state of structural collapse. The literature review and an experimental study on kaolin samples with a known stress history suggested that yield stress possesses certain dependency on the sampling direction. The anisotropy of yield stress for Battleford till from Birsay, Saskatchewan was also explored by testing directional oedometer samples. In addition, the anisotropy of stiffness was also investigated using a newly developed lateral stress oedometer that is capable of independent measurement of horizontal stresses at three different points with angles of 120 degrees. Preliminary evidence of a correlation between the direction of maximum stiffness in a horizontal plane and the known direction of glacial shear was observed. The correlation between the direction of maximum yield stress and known direction of glaciation was rather poor. Anisotropy of in situ stresses was investigated by conducting LCPM tests in Pot clay in the Netherlands. Based on the LCPM test results, it was concluded that the evidence of a correlation between the anisotropy of in situ stress and known direction of glacial advance is still rather obscure. Although both the laboratory studies and field studies cannot sufficiently confirm the existence of lateral anisotropy of geomechanical properties and its relationship to the direction of the Quaternary ice-sheet movement, the effects of subglacial shearing should not be neglected in assessing the geotechnical properties of glaciated soils. In practice, it is usually found that the preconsolidation pressure profile does not follow the gravitational line as predicted by the one-dimensional consolidation theory and its magnitude is not compatible with the measured effective pressure values at the base of the glacier. It has been suggested that changes in seepage gradient (upward or downward) are responsible for the deviation of preconsolidation pressure profile away from the gravitational line. In this thesis, a new glacial process model – consolidation coupled shearing – was proposed. This model is based on the framework of traditional soil mechanics (critical state theory, Modified Cam-clay model and one-dimensional consolidation theory) and is consistent with the general geological and glaciological evidences. This model may provide an alternative explanation for the preconsolidation pressure patterns generally observed in practice. It can also be combined with groundwater flow characteristics to explain the diversity of the preconsolidation consolidation patterns. The proposed model was used successfully to obtain the preconsolidation pressure profile observed in Battleford till at Birsay and the subglacial shear-softening phenomenon.en_US
dc.identifier.urihttp://hdl.handle.net/10388/etd-06082005-145640en_US
dc.language.isoen_USen_US
dc.subjectstiffnessen_US
dc.subjectpreconsolidation pressureen_US
dc.subjectcritical stateen_US
dc.subjectconsolidationen_US
dc.subjectload cell pressuremeteren_US
dc.subjectlateral stress oedometeren_US
dc.subjectin situ stressesen_US
dc.subjectanisotropyen_US
dc.subjectGlaciated Soilsen_US
dc.titleEffect of subglacial shear on geomechanical properties of glaciated soilsen_US
dc.type.genreThesisen_US
dc.type.materialtexten_US
thesis.degree.departmentCivil Engineeringen_US
thesis.degree.disciplineCivil Engineeringen_US
thesis.degree.grantorUniversity of Saskatchewanen_US
thesis.degree.levelMastersen_US
thesis.degree.nameMaster of Science (M.Sc.)en_US

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