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Geotechnical News • June 2013
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THESIS ABSTRACTS
Reusable Instrumented Test Pile for
Improved Pile Design in Granular Soils
Aravinthan Thurairajah
“Aran” Aravinthan Thurairajah, Ph.D., Junior Geotechnical Engi-
neer, Golder Associates Ltd. Burnaby, British Columbia, Canada,
Aran_Thurairajah@golder.com
Caltrans’ investment in driven piling to support bridges and
other structures has averaged about $25M/year over the last
decade. The systems constructed have performed well, but
conservatism exists due to uncertainties in soil properties,
pile drivability, soil-pile interaction, and pile setup. A new
method that could achieve modest saving of 5% in design
could save in excess of $1M per annum. This thesis pres-
ents the development of a reusable instrumented test pile
(RTP) as an in situ testing device for improved pile design
in granular soils (coarser than No. 200 sieve). The RTP
system consists of short instrumented sections that provide
measurements of axial load, radial stress, pore pressure,
and acceleration, and are connected in series with standard
Becker pipe sections. The RTP – Becker pipe string is
driven using the standard Becker pile driving hammer, and
the TRP system was designed to handle the high installation
stresses in granular soils while retaining sufficient resolution
in the instrumentation readings for subsequent analyses of
shaft and tip resistances. RTP measurements obtained during
driving provide detailed information regarding pile drivabil-
ity, measurements during static tests capture load transfer
along the pile, and measurements during pile setup capture
capacity gain over time. The design, fabrication, calibration,
proof testing, and full scale field deployment are presented
herein.
Thesis
Advisor:
Jason
T.
DeJong,
University
of
California, Davis, Associate Professor, Department of Civil and
Environmental Engineering, E:
Frost Heave: New Ice Lens Initiation
Condition and Hydraulic Conductivity
Prediction
Tezera Firew Azmatch
Tezera Firew Azmatch, tazmatch@ualberta.ca
Studies on frost heave indicate that significant frost heave
observed in the field or laboratory is attributed to ice lens
formation associated with water migration to the freezing
front and the segregational ice that develops. Hence frost
heave prediction models require ice lens initiation criteria
and hydraulic conductivity estimation method for the frozen
fringe. Existing frost heave prediction methods do involve
complex procedures of estimating the hydraulic conductiv-
ity. Ice lens initiation conditions by existing methods are
not also easy to implement. In fact, some of the exiting frost
heave prediction methods lack ice lens initiation condition.
The objective of this thesis is to investigate and develop ice
lens initiation criteria and hydraulic conductivity estima-
tion methods that are simple to implement in frost heave
prediction. Simple methods, involving the use of SFCC,
for predicting ice lens initiation condition and hydraulic
conductivity of the frozen fringe have been proposed and
verified in this study.
A new fundamental approach is proposed to determine the
ice lens initiation condition using the soil freezing character-
istics curve (SFCC). It is demonstrated that an ice lens initi-
ates close to the so-called ice-entry value defined using the
SFCC. Ice lens initiation conditions for different boundary
conditions were determined in a laboratory using the SFCC
and were then compared with the ice lens initiation condi-
tions from a one-dimensional open system frost heave tests.
The results using the SFCC showed good agreement with
the values determined experimentally.
A new approach, using the soil freezing characteristic curve
(SFCC), is proposed to estimate the hydraulic conductivity
of partially frozen soils. The hydraulic conductivity function
for partially frozen Devon Silt is derived using the SFCC
and the empirical relationships for hydraulic conductivity
estimation method developed by Fredlund et al (1994). The
SFCC for Devon Silt is determined from unfrozen water
content measurement using time domain reflectometry
and temperature measurements inside the soil sample. The
results using this novel approach compare well with results
presented by others that use different methods to determine
the hydraulic conductivity function of partially frozen soils.
Results from previous studies on frost heave indicate the
presence of freezing-induced cracks in the frozen fringe
(e.g., Arenson et al., 2008). These cracks affect the hydrau-
lic conductivity of the frozen fringe and hence the mois-
ture transfer process during frost heave. The presence of
the cracks necessitates the use of a dual porosity model
for estimating the hydraulic conductivity function of the
frozen fringe. This study proposed a dual porosity model for
estimating the hydraulic conductivity of the frozen fringe.
Hence, the hydraulic conductivity of the frozen fringe will
have two components: hydraulic conductivity of the soil
matrix and hydraulic conductivity of the cracks. Methods
are discussed to estimate the two hydraulic conductivity
components. The hydraulic conductivity of the cracked
frozen fringe is the estimated as the weighted average of
the two components based on the respective porosity ratio.
The proposed dual porosity hydraulic conductivity model is
then used to carry out parametric study of the influence of
the cracks on the hydraulic conductivity of the frozen fringe.
The results indicated that the cracks have considerable influ-
ence on the hydraulic conductivity of the frozen fringe while
taking only a few percent of the pore space.
Supervisor: D.C. Sego, University of Alberta, Civil &
Environmental Engineering, Edmonton, Alberta, Canada T6G 2G7,
T: 780-492-2176, F: 780-492-8198