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Permanent link (DOI): https://doi.org/10.7939/R3CD59

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Measuring Pore-water Pressure in Partially Frozen Soils Open Access

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Other title
Subject/Keyword
pore-water pressure
piezometer
thawing soils
Skempton parameters
frozen soils
freezing soils
effective stress in frozen soils
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Kia, Mohammadali
Supervisor and department
Dr. David C. Sego & Dr. Norbert R. Morgenstern
Examining committee member and department
Sego, David C. (Civil and Environmental Engineering Department, University of Alberta)
Blatz, James (Civil and Environmental Engineering Department, University of Manitoba)
Wilson, G. Ward (Civil and Environmental Engineering Department, University of Alberta)
Szymanski, Jozef (Civil and Environmental Engineering Department, University of Alberta)
Morgenstern, Norbert R. (Civil and Environmental Engineering Department, University of Alberta)
Arenson, Lukas (BGC engineer, previous post-doc at Civil and Environmental Engineering Department)
Rostron, Ben (Earth and Atmospheric sciences, University of Alberta)
Department
Department of Civil and Environmental Engineering
Specialization
Geotechnical Engineering
Date accepted
2012-10-02T11:43:20Z
Graduation date
2012-09
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Knowledge of pore-water pressure is essential to predict the ‘effective stress’ that controls the ‘resistance and deformation’ of a soil and to assess the ‘flow’ of water through it. Flow of water towards the freezing fringe controls the amount of frost heave in freezing soils. Drainage of this excess water controls subsequent thaw settlements as the frozen soil thaws. Further, the rate of dissipation of pore-water pressures control the thaw-instability in warming permafrost slopes. Not all of the water in a soil is ice at subzero temperatures; therefore, these soils are ‘partially frozen’. Hence, the challenges associated with measuring pore-water pressure distribution in freezing, thawing, and frozen soils can all be considered as one category: measuring pore-water pressures within a ‘partially frozen soil’. Therefore, measurement of pore-water pressures in partially frozen soils and having methods for estimating the pore-water pressure response to the applied loads are desirable. In this research, first a new instrument was developed to accurately conduct these measurements. Then, the measured pore-water pressures were used to study stress transmission within a partially frozen soil under applied loads, as well as under warming conditions. It was shown that if a sufficient amount of unfrozen water exists in a soil at subfreezing temperatures, it provides a continuous liquid phase that transfers pressures independent from the solid phase. Therefore, effective stress material properties and analysis should be used to evaluate the resistance and deformation of these partially frozen soils. This is of practical significance in analyzing stability and in modeling constitutive behavior of soil masses in warm and warming permafrost, especially for assessing geohazards associated with climate change. It is also of practical significance in analyzing and designing foundations, retaining structures, underground facilities, and frozen-core dams in cold regions. For the first time, measurements of Skempton’s B-bar coefficient in a partially frozen soil at various initial void ratios were presented and compared to that of the unfrozen soil. Thus, by assuming superposition, stress distribution between the soil matrix, pore-ice, and pore-water was evaluated. Further, decrease in load bearing of the ice matrix with increasing temperature was evaluated via measuring pore-water pressure distribution within a partially frozen soil during undrained warming. It was also found that in both the partially frozen and unfrozen states, the pore-water pressure response of overconsolidated sand is bilinear with a well-defined inflection point. Further, it was shown that the change in effective stress under undrained loading is not zero in overconsolidated sand specimens; hence, frictional resistance is not zero under undrained loading due to the stiffer solid phase.
Language
English
DOI
doi:10.7939/R3CD59
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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