Advances in Offshore Seismic Slope Stability: A Case History
This paper presents a case history showing how the integration of detailed geophysical and geotechnical data and advanced numerical modeling can overcome the limitations of conventional analysis in predicting seismic stability of deepwater slopes. Submarine landslides represent one of the most critical geohazards for offshore pipelines and deepwater hydrocarbon developments. This is particularly true for seismically active regions where earthquakes are expected to be a triggering mechanism. A typical issue encountered in these cases is the coexistence of several detrimental aspects: poor geomechanical properties of shallow sediments; presence of steep slopes; and/or severe seismic input. The combination of these aspects often makes it difficult to match results of conventional pseudo-static slope stability analysis with field observations. These methods are generally conservative for deepwater conditions and are not able to reproduce observed past failures modes. This case history is of a complex slope system in the Mediterranean Sea. Morphologically the system presents a number of canyons and large-scale landslide features, overlain by a limited number of shallow planar slides. Geochronological testing constrained the large, deep slides to the distant past while confirming the shallow slides as recent phenomena. The use of high quality sampling and advanced laboratory tests provided the necessary input for dynamic nonlinear FEM analyses using OpenSees software. Numerical results based on a set of real time histories confirmed field observations and highlighted the possible formation of seismically triggered shallow slides. The paper describes how geophysical data, accurate soil sampling and advanced laboratory testing together with an advanced numerical model can develop reliable slope stability assessments for projects in difficult environmental conditions.
KeywordsSubmarine landslide Advanced geotechnical testing Seismic slope stability Dynamic numerical modeling Marine geophysics Marine geohazards
We would like to thank William J. Johnson and Federico Pisanò for their valuable review and improvement of the manuscript.
- EN 1998–5 (2004) Eurocode 8: design of structures for earthquake resistance – Part 5: foundations, retaining structures and geotechnical aspects. European Committee for Standardization (CEN), Brussels, BelgiumGoogle Scholar
- Kondner RL (1963) Hyperbolic stress-strain response: cohesive soils. J Soil Mech Found Div 89(SM1):115–143Google Scholar
- Kramer SL (ed) (1996) Geotechnical earthquake engineering. Prentice Hall, Upper Saddle RiverGoogle Scholar
- Lunne T, Berre T, Andersen KH, Strandvik S, Sjursen M (1997) Sample disturbance effects in soft low plastic Norwegian clay. In: Proceedings of the conference on recent developments in soil and pavement mechanics, Rio de Janeiro, Brazil, 25–27 June 1997Google Scholar
- Lysmer J, Kuhlemeyer RL (1969) Finite dynamic model for infinite media. J Eng Mech Div ASCE 95(EM4):859–877Google Scholar
- Magagnoli A (2003) “CP-20” Carotiere a pistone per carote di sedimento lunghe fino a venti metri. Rapporto Tecnico n. 83. CNR – ISMAR, BolognaGoogle Scholar
- Pacific Earthquake Engineering Research Center (2010) Open system for earthquake engineering simulation (OpenSees). http://opensees.berkeley.edu. Accessed 20 Feb 2010
- Parra E (1996) Numerical modelling of liquefaction and lateral ground deformation including cyclic mobility and dilation response in soil systems. PhD thesis, Department of Civil Engineering, Rensselaer Polytechnic Institute, Troy, NYGoogle Scholar
- Yang Z (2000) Numerical modelling of earthquake site response including dilation and liquefaction. PhD thesis, Department of Civil Engineering and Engineering Mechanics, Columbia University, New YorkGoogle Scholar