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OCE 582 Seabed Geomechanics Kate Moran Term paper, Fall 2008 Kevyn Bollinger

Earthquake Induced Pore Pressures in Slope Failures: How earthquakes can generate excess pore pressures in marine sediments leading to liquefaction and slope failure. OCE 582 Seabed Geomechanics Kate Moran Term paper, Fall 2008 Kevyn Bollinger. Why are we interested in marine slope failures?.

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OCE 582 Seabed Geomechanics Kate Moran Term paper, Fall 2008 Kevyn Bollinger

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  1. Earthquake Induced Pore Pressures in Slope Failures:How earthquakes can generate excess pore pressures in marine sediments leading to liquefaction and slope failure. OCE 582 Seabed Geomechanics Kate Moran Term paper, Fall 2008 Kevyn Bollinger

  2. Why are we interested in marine slope failures? Underwater landslides: • Harm structures • Pipelines • Offshore platforms • May induce tsunamis which: • Consist of shorter waves than seismic tsunamis • Increased dispersion and interferences • Occur on the shelf • Propagation of only a few minutes to tens of minutes • Have energy concentrated on short sections of coastline • Large runup and inundation (El Bettah et. al., 2008)

  3. Cyclic loading Pore pressure increases in undrained conditions Soil strength decreases Landslide Possible tsunami Earthquakes and Failures/Tsunamis:What’s the link? Pore pressure: Inter-granular fluid pressure in a soil If the strength of soil on a slope decreases enough, a failure could occur (El Bettah et. al., 2008)

  4. Pore Pressure & Soil Strength Liquefaction and instability phenomena occur when the pressure exerted by the fluid on the particles approaches or counterbalances the inter-granular forces <http://www.ce.washington.edu/~liquifaction/html/why/why1.html >

  5. Excess Pore Pressure Generation Residual excess pore pressure builds up under cyclic input. • Waves (cyclic water pressure) • Cyclic loads on soil matrix (modeled by cyclic tri-axial test) • Seismic events • Man-made structure vibrations/ cyclic movements (de Groot M.B., Bolton M.D. et al., 2006)

  6. Cyclic Loads on Soil Matrix Yang J. et. al., 2001, found: • The influence of vertical motion is small. • Vertical ground motion relation to Horizontal ground motion important. • In-situ measurements and modeling.

  7. Triaxial Cell Sediment Sample Cyclic Triaxial Tests • Experimental procedure to study soil behavior under cyclic loading • Inter-granular pore pressure builds up with cycles. Ottawa Sand (Bradshaw and Baxter, 2007)

  8. Cyclic Triaxial Tests Small Glass Beads, 10-50mm, Silt Deviator Stress Axial Strain Sediment Sample DA Strain Pore Pressure Ratio (D. Gemme, 2008)

  9. Stress Strain Accumulation (Niemunis A. 2006)

  10. Stress Strain Accumulation (Niemunis A. 2006)

  11. Conclusion / Thesis Work Conclusions: • Horizontal and Vertical motions cause accumulation of strain and pore pressure. • Liquefaction when pore pressure increases faster than dissipates. • Cyclic Stress/Strain paths determine rate. My Thesis: (In partnership with URI-OE PhD Cand. Myriam El Bettah) • Lab testing paired with Lattice-Boltzmann Numerical Modeling (micro-fluidic based with macro scale observations). • Better the understanding of these processes.

  12. Suggested Reading for Failures Around Structures Journal of Waterway Port Coastal and Ocean Engineering, vol132 no4. Special issue on liquefaction phenomena, July/August 2006. • Foray P. et. al. (2006) “Fluid-Soil-Structure Interaction in Liquefaction around a Cyclically Moving Cylinder”, pgs 289-299. • de Groot M.B., Kudella M., et. al. (2006) “Liquefaction Phenomena underneath Marine Gravity Structures Subjected to Wave Loads”, pgs 325-335. • Kudella M. et al. (2006) “Large-Scale Experiments on Pore Pressure Generation underneath a Caisson Breakwater”, pgs 310-324. • Mutlu Sumer B. et. al. (2006) “Liquefaction around Pipelines under Waves”, pgs 266-274

  13. References El Bettah M., Grilli S.T., Baxter C.D.P., Bollinger K., Krafczyk M., Janßen C. (2008), “A Microfluidics Study of the Triggering of Underwater Landslides by Earthquakes”, Proceedings of the 2008 ISOPE Conference, Vancouver Canada. Gemme, D.A. (2008) “Effect of Particle Size on Dynamic Pore Pressure Buildup in Soils”, Master’s Thesis, Dept. of Ocean Engng., Univ. of Rhode Island, 88 pgs. de Groot M.B., Bolton M.D., Foray P., Meijers P., Palmer A.C., Sandven R., Sawicki A., Teh T.C., (2006) “Physics of Liquefaction Phenomena around Marine Structures”, Journal of Waterway Port Coastal and Ocean Engineering, vol 132 no 4, pgs 227-243. Niemunis A., Wichtmann T., Triantafyllidis T. (2006) “Long term Deformation in Soils due to Cyclic Loading”, Modern Trends in Geomechanics, Springer Berlin Heidelberg, pp 427-462. Yang J., Sato T., Savidis S., Li X. S. (2002), “Horizontal and vertical components of earthquake ground motions at liquefiable sites”, Soil Dynamics and Earthquake Engineering, vol 22 no 3. Zeghal M., El Shamy U. (2004) “Dynamic response and liquefaction of saturated granular soils: a micromechanical approach,” Cyclic Behaviour of Soils and Liquefaction Phenomena. Taylor & Francis Group, London.

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