This project was  terminated in 2008.

 

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

• Modelling and understanding of submarine and subaerial debris flows - based on experimental studies
• Subaerial debris flows and landslides ¿ dynamics and predictions
• 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:

• turbidity current on top
• nearly laminar layer of moving clay and fluidized sand
• settled sand layer at the bottom

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".