The Impact of soil structure and confining stress on the permeability of clay soils in brine environments
Date
1990
Authors
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Journal ISSN
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Publisher
ORCID
Type
Degree Level
Masters
Abstract
In recent years, numerous studies have been done on the alteration of the permeability of
clayey soils as a result of exposure to concentrated organic or inorganic permeants. These
permeability changes have been attributed to either changes in the microfabric or the
macrofabric of the clays as a result of physico-chemical interactions between the clay
particles and pore fluid chemistry. However at the present there still remains no
theoretical framework for interpreting the mechanism for changing permeability and the
prediction of the onset of permeability alterations during osmotic consolidation.
In this thesis, focus is given to the impacts of initial soil structure and vertical confining
stress on the changes of permeability that occur in a clayey soil when it is exposed to
brine. Different methods of sample preparation are included so that the effect of different
soil structure can be observed. In addition the permeability tests were carried out at
different stress levels. The initial soil structure and changes in structure as a result of
changes in pore fluid chemistry were obsetved using Scanning Electron Microscope
photographs. Two sample failure criteria based on the measurement of the change in the
physico-chemical stress, (R-A), are proposed in order to predict the onset permeability
alterations.
The test results reveal that the alteration of permeability is strongly related to the initial
soil structure and level of confining stress. No significant change in the microfabric of
the clay was observed; however, the macro pore size of the specimens appears to increase
as a result of physico-chemical interaction of clay particles and NaCl brine. The
permeability increases in a continuous manner with decreases in confining stress and can
be related to the control of horizontal osmotic volumetric strain within the soil.
The two sample failure criteria, based on the release of (R-A) and loss of confining stress
in soils after brine permeation, seem to provide a simple and effective approach to predict
the onset of permeability alteration in soil as a result of brine exposure. This demonstrates
that the mechanism for the onset of permeability alteration can be attributed to the
increase in the size of the macropores and the loss of confmement in the soil, rather than
changes in microfabric.
(Appendix D & E were duplicated in the original)
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Degree
Master of Science (M.Sc.)
Department
Civil Engineering
Program
Civil Engineering