Geotechnical News June 2011
51
THESIS ABSTRACTS
Comparison of Geoenvironmental
Properties of Caustic and Noncaustic
Oil Sand Fine Tailings
Warren Gregory Miller
Warren Gregory Miller, Worley Parsons,
A study was conducted to evaluate the properties and processes
influencing the rate and magnitude of volume decrease and strength
gain for oil sand fine tailings resulting from a change in bitumen ex-
traction process (caustic versus non-caustic) and the effect of adding
a coagulant to caustic fine tailings.
Laboratory flume deposition tests were carried out with the ob-
jective to hydraulically deposit oil sand tailings and compare the
effects of extraction processes on the nature of beach deposits in
terms of geometry, particle size distribution, and density. A good
correlation exists between flume deposition tests results using oil
sand tailings and the various other tailings materials. These com-
parisons show the reliability and effectiveness of flume deposition
tests in terms of establishing general relationships and can serve as
a guide to predict beach slopes.
Fine tailings were collected from the various flume tests and a
comprehensive description of physical and chemical characteristics
of the different fine tailings was carried out. The characteristics of
the fine tailings is presented in terms of index properties, miner-
alogy, specific surface area, water chemistry, liquid limits, particle
size distribution and structure. The influence of these fundamen-
tal properties on the compressibility, hydraulic conductivity and
shear strength properties of the fine tailings was assessed. Fourteen
two meter and one meter high standpipe tests were instrumented
to monitor the rate and magnitude of self-weight consolidation of
the different fine tailings materials. Consolidation tests using slurry
consolidometers were carried out to determine consolidation prop-
erties, namely compressibility and hydraulic conductivity, as well
as the effect of adding a coagulant (calcium sulphate [CaSO4]) to
caustic fine tailings. The thixotropic strength of the fine tailings was
examined by measuring shear strength over time using a vane shear
apparatus.
A difference in water chemistry during bitumen extraction was
concluded to be the cause of substantial differences in particle size
distributions and degree of dispersion of the comparable caustic
and non-caustic fine tailings. The degree of dispersion was consis-
tent with predictions for dispersed clays established by the sodium
adsorption ratio (SAR) values for these materials. The biggest ad-
vantage of non-caustic fine tailings and treating caustic fine tailings
with coagulant is an increased initial settlement rate and slightly
increased hydraulic conductivity at higher void ratios. Thereafter,
compressibility and hydraulic conductivity are governed by ef-
fective stress. The chemical characteristics of fine tailings (water
chemistry, degree of dispersion) do not have a significant impact
on their compressibility behaviour and have only a small influence
at high void ratio (low effective stress). Fine tailings from a caustic
based extraction process had relatively higher shear strengths than
comparable non-caustic fine tailings at equivalent void ratios. How-
ever, shear strength differences were small and the overall impact on
consolidation behaviour, which also depends on compressibility and
hydraulic conductivity, is not expected to be significant.
Supervisors: D. Sego, J.D. Scott, Dept. of Civil & Environmental
Engineering, University of Alberta
Subsurface Behavior of Spilled Fuel in a
Permafrost Environment
Olumide Iwakun
Olumide Iwakun,
This dissertation focuses on the subsurface behavior of spilled
fuel consisting of diesel and gasoline, which are subsets of light
nonaqueous phase liquids (LNAPLs), in a permafrost environment.
Particular emphasis is laid on mobile LNAPL in fractured bedrock.
The site chosen for this study is the abandoned Colomac
gold mine, 220 kilometers northwest of Yellowknife in the North-
west Territories, where over 50,000 liters of spilled fuel occurred
between 1990 and 2003. The site is underlain by fractured bedrock
with 0 to 4.6 m of overburden soil. The broad objectives of this work
involve determination of contamination extent and LNAPL behav-
ior at the site. Other specific objectives include determination of
the major geochemical processes and identification of mechanisms
influencing LNAPL movement and accumulation at the site.
Both field and laboratory studies were performed to achieve the
above-stated objectives. The field study involved site characteriza-
tion, and the laboratory study involved a topdown freezing experi-
ment using a freezing cell, consisting of parallel glass plates, to
evaluate the impact of cyclic freeze-thaw on LNAPL movement.
The site characterization efforts showed that the LNAPL contamina-
tion is limited to the upper section (~7 m) of the fractured bedrock.
The field study showed that water table fluctuations and freezing-
induced displacements were active but discontinuous mechanisms
contributing to LNAPL migration and accumulation in the forma-
tion and monitoring wells at the site.
Analyses of the groundwater suggested ongoing anaerobic bio-
degradation of the dissolved LNAPL components. Furthermore, the
analyses showed that the water was CaSO4 type and the main geo-
chemical processes were gypsum dissolution and carbonate weath-
ering. The analyses underscored the importance of bedrock miner-
alogical composition on groundwater constituents and geochemical
processes.
The laboratory test results involving entrapment of diesel fuel
below the water column and admixture of soluble oils with water in
the freezing cell showed upward mobility of LNAPL under cyclic
freezing, and downward progressive expulsion of the soluble oils
ahead of the advancing freezing front. The results corroborated lit-
erature findings on cryogenic expulsion ahead of freezing front, and
