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Project
9:
Slide dynamics and mechanics of disintegration (finished end of 2008)
Project Manager: Anders Elverhøi (UiO)
 
Introduction
Gravity mass transport represents a major
hazard on land as well as in the ocean or in lakes. In order to be able
to predict possible runout distances and the forces exerted on
structures (obstacles) in the path of the slide, there is a need for
better understanding of the flow dynamics including more advanced
numerical models. It is also important to increase our knowledge of how
“solid” materials are disintegrating into “flowing” materials. Thus, a
major challenge is to be able to predict possible flowing behaviour of a
certain type of material based on its geotechnical properties. We
foresee a stepwise development of our work and start where the group has
been strongly involved for the last period and have identified highly
needed “improvements”.
 
Figure 1. Left: Snapshot of debris flow
front in subamarine laboratory experiment. Right: The experimental flume
at St Anthony Falls Lab seen from above. Photos: Hedda Breien.
Themes in 2007
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Modelling and
understanding of submarine and subaerial debris flows – based on
experimental studies
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Subaerial debris flows
and landslides – dynamics and predictions
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Program development –
numerical models for sub aqueous and sub aerial debris flows
Introduction
Gravity mass transport
represents a major hazard on land as well as in oceans and lakes. In
order to be able to predict possible runout distances and the forces
exerted on structures (obstacles) in the path of the slide, there is a
need for a better understanding of the flow dynamics, including more
advanced numerical models. It is also important to increase our
knowledge of how “solid” materials are disintegrating into “flowing”
materials. Thus, a major challenge is to be able to predict possible
flowing behaviour of a certain type of material based on its
geotechnical properties.
How do we work?
Our work combines a basic
understanding of the physics involved and numerical simulations with
field observations and experiments in laboratory. In 2006 a series of
comparable sub aerial and sub aqueous experiments was performed at the
St Anthony Falls Lab in Minneapolis. These experiments provide data that
clarify the differences and similarities of how mass moves under water
compared to on land.
Objectives
Our objective is to
increase our knowledge of flow regimes of debris flows of varying
composition. Although several numerical models for mass movements have
been developed and presented, there is an ongoing discussion on which
concepts and models should be applied to the different types of material
and flow regimes. Roughly, the approaches can be divided into a granular
approach versus a viscoplastic approach. A main goal for our work is to
develop models that are able to handle situations with variable mixtures
of granular versus cohesive materials. Analysis of field and
experimental data will be an important tool in this process.
Results
Our experimental studies
of debris flows represent mass movements on the bottom of the sea floor
as well as debris flows on land. These experiments help us understand
how sub aqueous mass movements can move over large distances on very low
slopes, how deep water sandy bodies are generated as well as to prevent
geohazards connected to oil and gas installations. The main results from
the experimental studies until now are summarized below.
1) 3 Layers: A clay-sand
mixture stratifies into 3 layers immediately after release:
2) Hydroplaning: The
moving mass develops a hydroplaning head, moving 3 times faster than the
rest of the debris flow body.
3) Stretching: The fast
moving head and the slower moving body result in stretching of the mass
and a change (softening) of the geotechnical properties due to reduced
friction under the hydroplaning head, shearing of the mass and water
intrusion from the cushion underneath. This is again believed to
facilitate the fast movement and long runout and may result in outrunner
blocks.
Ongoing activities
Theme 1:
Fluid and granular flow dynamics – gravity mass flows and the origin of
deep water sandy bodies.
Ph. D. student: Hedda Breien. Project leader:
Anders Elverhøi and Kaare Høeg. Other collaborators: Fabio V. De Blasio,
Dieter Issler, Johan Petter Nystuen. External Institutes: Simula senter,
Oslo, St. Anthony Falls Lab, Minnesota, USA, and Department of Applied
Mathematica, Oslo, University of Pavia, Italy.
The basic concept in
the actual project is to elucidate the fundamental parts in gravity mass
flows, particularly in the sub aqueous environment. We investigate the
physical-mechanical conditions of mass movements based on i) experiments
with artificial slurries of different composition and ii) numerical
modelling.
Project summary for
2006
In the year 2006,
Hedda Breien carried out a unique set comparable subaerial and submarine
laboratory experiments at the SAFL in Minnesota. The experiments include
a suite of tests varying the composition from almost pure granular to
fully viscoplastic as well as the ambient environment from air to water.
We see this rather fundamental approach as needed due to the fact that
up to now an integrated interpretation has been hampered by
disagreements and individuality in dealing with these different fields
of mass movement.
Observations as well
as experimental studies seem to indicate important and significant
differences between mass flows in air with respect to water, although we
are dealing with the same principles of driving forces. As events in the
sub aerial environment are far more accessible than their sub aqueous
counterparts, it is useful to identify the differences and similarities
in their behaviour. Fundamental understanding of the dynamics will also
make it possible to use the right type of knowledge from sub aerial
deposits, flow observations and modelling in the sub aqueous field and
vice versa.
Plans
During the
following years we also plan to commence work at a computer model for
the flow of sandy debris flows. From this long-term effort, which will
probably involve also the SIMULA computing center, we expect to develop
more advanced numerical models capable of handling 3D problems.
Theme 2:
Landslide characterization in Central America with particular emphasis
on Nicaraguan cases
Ph. D. student: Graziella Devoli. Project leader: Kaare Høeg.
Other collaborators: Anders Elverhøi, Farrokh
Nadim, Fabio De Blasio, B. Romstad, B.
Etzelmuller. External research Institutes:
INETER (Managua, Nicaragua), and Department of Geography, University of
Oslo.
The first part
“Landslide database for Nicaragua” included the first design and
development of a national landslide database made in collaboration with
the Instituto Nicaraguense de Estudios Territoriales (INETER) in
Nicaragua. This phase started with the collection and integration of
historical and recent available landslide events in form of spatial and
thematic data. Landslide information was collected from historical
documents, newspapers, technical reports and landslide inventory maps
prepared after Hurricane Mitch (1998). The information contained in the
database (first update) was used for descriptive analysis at national
and regional scale to define the spatial and temporal distribution,
types of mass movements and triggering mechanisms and to analyze the
influence of topographic (elevation, slope
angle, slope aspect) and lithological parameters on the occurrence of
landslides.
In the second part
“Statistical analysis of Nicaraguan landslides” landslide data from the
Nicaraguan database and a few data from other Central American countries
have been used to analyze, through empirical-statistical methods, the
relationships between the most important parameters of landslides and in
particular debris flows in order to predict run-out distance, necessary
for debris flow hazards assessment. The relations proposed will be
compared with similar relationships available in literature and used to
calibrate numerical simulations models.
In the third part “Use
of mechanical/dynamical models to back-analyze one or more Nicaraguan
debris flows” the Casita lahar has been chosen to reconstruct the mode
and sequence of the 1998 flank failure in order to understand the
mechanism of the landslide. The remaining slope instability will be
modelled as well.
Plans
This PhD is to be finished early 2007.
Theme 4:
Flow modelling of submarine slides (part of the Euromargin programme).
Anders Elverhøi, Fabio De Blasio, C. Harbitz, P.
Gauer, D. Issler.
Further activity will
include numerical modelling of submarine clay-rich debris flows,
modelling of sand rich debris flows (this part is related to Theme 1). A
modified version of the depth-integrated program BING (originally from
St. Anthony Falls Labs, Minnesota) previously used for a series of
projects will be re-written in a more friendly fashion. Further, we will
continue our ongoing studies on the mechanics of disintegration,
break-up and segregation in sub aqueous slides. Numerical studies on the
flow of outrunner blocks will also be continued. We also plan to
cooperate with project 10 (Carl Harbitz) on the problem of tsunami
generation by submarine landslides.
National and
International cooperation
- St. Anthony Falls
Laboratory, University of Minnesota, USA
- Department of Civil
and Environmental Engineering and the Department of Geology,
University of Illinois, USA
- Earth and Ocean
Sciences Division, Duke University, USA
- Simula Research
Senter, Oslo, Norway
- Department of Earth
and Ocean Sciences, University of British Columbia.
- Department of
Geosciences, University of Oslo
- Norwegian
geotechnical Institute (NGI)
Key personnel
Anders Elverhøi
Fabio V. De Blasio
Dieter Issler
Peter Gauer
Fridtjov Irgens
Ph.D-students
Hedda Breien
Graziella Devoli
Publications:
Papers
Breien, H., De Blasio, F.V., Elverhøi, A. and Høeg, K..
”Erosion, morphology and dynamics of a debris flow
caused by a glacial lake outburst flood.”
Submitted to “Landslides”.
Breien, H., Elverhøi,
A., De Blasio, F., Issler, D.. “Experimental studies
of debris flows – fundamentals of submarine vs subaerial dynamics”
Abstract submitted to “3. International Symposium on Submarine mass
movements and their consequences”.
Devoli G. (2005) -
Collection of data on historical landslides in Nicaragua. In
“Landslides, risk Analysis and Sustainable Disaster Management” Sassa
K., Fukuoka H., Wang F., Wang G., (eds) proceedings of the First General
Assembly of the International Consortium on Landslides (Washington, USA,
12-14 October 2005).
Devoli, G., Morales,
A., and Høeg K. 2006. Historical landslides in Nicaragua - collection
and analysis of data [online]. Landslides. DOI
10.1007/s10346-006-0048-x. Published online 28 July 2006. (ICG
publication #126).
Devoli G., Strauch W.,
Chávez G., Høeg K. (2007). A landslide
database for Nicaragua: a tool for landslide hazard management [online].
Landslides. DOI 10.1007/s10346-006-0074-8. Published online 9 January
2007. (ICG publication #132)
Devoli G., De Blasio F.,
Elverhøi A., Høeg K., (submitted). Statistical
analysis of landslide events in Central America and prediction of
run-out distance. Submitted to the Canadian Geotechnical Journal
Devoli G., Cepeda J.,
Kerle N., Høeg K., (In preparation).
Geotechnical Modelling of the 1998 Casita volcano flank failure and
remaining slope instability.
Presentations
Elverhøi, A., De Blasio, F., Issler, D., Nystuen, J. P., Gauer, P.,
Harbitz, J. B., Marr, J.. ”Flow,
disintegration and lubrication of clay – sandy debris flows. From the
laboratory to the field.” Held at “AAPG”.
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