Numerical Analysis of the 650,000 m2 Åknes Rock Slope based on Measured Displacements and Geotechnical Data

  • Vidar Kveldsvik
  • Herbert H. Einstein
  • Bjørn Nilsen
  • Lars Harald Blikra
Original Paper


The unstable 650,000 m2 Åknes rock slope (Western Norway) poses a hazard, as a sudden failure may cause a destructive tsunami in the fjord. In this study the slope was divided into blocks based on displacements measured at the slope surface. Discontinuous deformation analysis (DDA) showed that three or four blocks in the upper half may be considered as potential subareas that may fail catastrophically. The lower half may be divided into two or three blocks, but more limited data introduces more uncertainty into block definition. The Universal Distinct Element code (UDEC) was used for two-dimensional (2D) stability analyses. By varying fracture geometry, fracture friction, and groundwater conditions within reasonable limits based on site-specific data a number of possible models were compared. The conclusions show that models that were unstable to great depths were in closer agreement with shear strength parameters derived from an earlier study than models that were unstable to smaller depths. The length (depth) of the outcropping fracture, along which shear displacements are shown to occur, plays an important role. A (shallow) slide at 30 m, in which displacements have been documented by borehole measurements, will reduce the stability at greater depths. Increased groundwater pressure is demonstrated to be less critical for very deep slope instability. The results of the DDA and UDEC modelling will be useful for planning of future investigations, interpretation of the subsequent results, further development of the early warning system and in the tsunami modelling.


Landslides Displacement analysis Numerical modelling DDA-Backward UDEC 



The work presented here is part of ongoing projects funded by the Research Council of Norway through the International Centre for Geohazards (ICG), the Geological Survey of Norway (NGU), Norwegian Geotechnical Institute (NGI), Norwegian University of Science and Technology (NTNU), National Fund for Natural Damage Assistance and Møre & Romsdal County, and the Aaknes/Tafjord project. The DDA-Backward analysis was done while the first author stayed at University of California, Berkeley. The first author wishes to thank Prof. Nicholas Sitar for hosting the stay and for useful discussions during the work. Thanks are also due to Dr. Gen-Hua Shi who suggested doing the DDA-Backward analysis and who taught the method.


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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Vidar Kveldsvik
    • 1
    • 2
  • Herbert H. Einstein
    • 3
  • Bjørn Nilsen
    • 2
  • Lars Harald Blikra
    • 2
    • 4
  1. 1.Norwegian Geotechnical Institute/International Centre for GeohazardsOsloNorway
  2. 2.Norwegian University of Science and TechnologyTrondheimNorway
  3. 3.Department of Civil and Environmental EngineeringMassachusetts Institute of TechnologyMAUSA
  4. 4.Geological Survey of NorwayTrondheimNorway

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