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Geotechnical News • June 2014
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THESIS ABSTRACTS
conducted in this work; and (5) values for the maximum
vertical oblique soil restraint diminish as the inclination
of the angle of breakout of buried pipelines increases with
respect to the horizontal.
Sponsoring Professor: Dr. Dharma Wijewickreme, Uni-
versity of British Columbia, 6250 Applied Science Lane,
Vancouver, B.C., Canada V6T 1Z4 / Office: (604)-822-5112 (Direct)
Fax: (604)-822-6901, email: dharmaw@civil.ubc.ca
Quantitative Risk Assessment of Natural
and Cut Slopes: Measuring Uncertainty in
the Estimated and Proposed Framework for
Developing Risk Evaluation Criteria
Renato Macciotta
Renato Macciotta, University of Alberta, NREF 1-035, Edmonton,
AB Tel: 780-862-4846, email: macciott@ualberta.ca
Understanding and limiting the risks inherent to natural and
cut slopes are now recognized to be a priority in achieving
an acceptable quality of life. Various methods of risk man-
agement that have been proposed in the last three decades
have evolved into a general framework for landslide risk
management. In particular, quantitative risk assessments can
assist in communicating risks. They also provide a clear and
systematic framework to analyze slope failure processes,
from origin, to movement, to consequence; and the effect of
different remedial works and strategies.
Some of the challenges and perceived limitations of quanti-
tative risk assessments are related to the necessary input of
expert opinion when estimating the risk levels in a quantita-
tive manner. One objective of this work is the systematic
assessment of the uncertainties in the estimated values of
risk. Quantitative risk analyses are carried out for two case
histories, where population of the analyses input param-
eters is done as probability distributions rather than fixed
values. The probability distributions of the input parameters
cover the range of values believed realistic for each input
parameter. The risk is then estimated through a Monte Carlo
simulation technique, and the outcome of the analysis is a
probability distribution of the estimated risk. This method-
ology shows the potential for evaluating the uncertainties
related to risk estimations.
The full potential of the risk management framework is best
met with the establishment of risk evaluation criteria. The
other objective of this work focuses on the development of
risk evaluation criteria. It is not the intention of this work to
develop case specific criteria, as this responsibility should
lie with owners and regulators, but to propose a framework
for developing the criteria, where the risk analyst takes an
active role.
A summary of the state of practice for quantitative risk
assessments is included as part of the thesis. The work on
the evaluation of uncertainty related to the estimated risks
and a proposed framework for developing risk evaluation
criteria are then presented. The last two chapters of the
thesis present a summary of the research results, conclusions
and proposed future research.
Supervisor: C. Derek Martin, Geotechnical and Geoenvironmen-
tal Group, Department of Civil & Environmental Engineering,
University of Alberta, 3-133 Markin/CNRL Natural Re-
sources Engineering Facility, Edmonton, Alberta T6G 2G7,
Tel: 780-492-2176, Fax: 780-492-8198
High Stress Flow Behaviour and
Constitutive Modeling of Dry Granular
Materials
Abraham Enawgaw Mineneh
Abraham Enawgaw Mineneh, Levelton Consultants Ltd.,
8884 – 48
th
Avenue, Edmonoton, AB T6E 5L1
Landslides include various forms of geological mass
movements such as falls, slides and flows under the force
of gravity. Predictions of landslide kinematics and dynam-
ics require knowledge of flow behavior and mathematical
modeling. Research into the flow behavior of granular
materials has revealed the existence of rate-dependent
frictional behavior at high shear rates and void ratios as well
as ratedependent frictional behavior as low shear rates and
void ratios. However, the results of high stress shear experi-
ments on small particles indicate that shear rate has no effect
on flow behavior. Following this finding, most geotechnical
analyses of landslides have considered mainly frictional
flow behavior. Since the collisional behaviour of granular
materials depends on particle inertia, both shear rate and
particle mass (or particle density and diameter) are equally
important in its occurrence. In this research, the relevance
of ratedependent collisional behavior flow behavior at high
stress was reinvestigated using simulation experiments on
large size particles. The results indicate that ratedependent
flow behavior is more likely to occur in rapidflow landslides
involving large particles, such as debris avalanches and rock
avalanches. The critical state framework which captures the
frictional behavior was extended to capture ratedependent
collisional behavior by adding shear rate as an additional
state variable, based on the pioneering work of Campbell.
The extended framework was used for flow classification,
study of flow progress, and constitutive modeling. The
effect of particle shape on granular flow behavior and the
extended critical state framework was reviewed using simu-
lation experiments.
Selected unified constitutive models proposed by Sav-
age and Louge were evaluated using the extended critical
state framework. In this research, new unified constitutive
model is developed. The new model combines the frictional
collisional stress contributions using weighting functions
called stress coefficients to determine the total stress. The
stress coefficients are interdependent and are determined
using empirical equations and detailed theoretical analyses.
The new model is used to predict the extended critical state