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P.B. Flemings (1), I. Song (2,3) and D.M. Saffer (3)

Laboratory investigation of coupled deformation and fluid flow in mudrock: implications for slope stability in the Ursa Basin, Gulf of Mexico. P.B. Flemings (1), I. Song (2,3) and D.M. Saffer (3) (1) Jackson School of Geosciences, University of Texas, Austin, USA

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P.B. Flemings (1), I. Song (2,3) and D.M. Saffer (3)

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  1. Laboratory investigation of coupled deformation and fluid flow in mudrock: implications for slope stability in the Ursa Basin, Gulf of Mexico P.B. Flemings (1), I. Song (2,3) and D.M. Saffer (3) (1) Jackson School of Geosciences, University of Texas, Austin, USA (2) Korea Institute of Geoscience and Mineral Resources, Korea (3) Department of Geosciences, Pennsylvania State University, USA

  2. Location of Ursa Basin, GOM Gulf of Mexico

  3. Mud/clay MTDs Seismic Profile: IODP Exp. 308 (Flemings et al., 2005)

  4. Objectives • Characterization of consolidation and shear behaviors of core samples from IODP Sites U1324 in the Ursa Basin, GOM • Estimation of the in situ state of stress and pressure during sedimentation • Analysis of slope stability in the continental slope at passive margin in the Ursa Basin, GOM

  5. Description of the sedimentary basin at Site U1324 • Sample depth: 30 ~ 160mbsf • Clay content: 40 ~ 60% • Consolidation coefficient: ~2.2 x 10-8 m2/sec • Sedimentation rate: >10mm/y. • Slope: ~2º

  6. shear unloading reloading sedimentation Stress path K0 line active failure line p’ q passive failure line

  7. Triaxial Pressure System Load signal load cell Oil Brine sample GDS pump GDS pump vacuum vacuum vacuum Base pressure Pore pressure Confining pressure Axial force

  8. Electric Devices load signal temperature signal load cell axial LVDTs radial LVDT radial caliper base pedestal LVDT signals pressure vessel base

  9. Test Record: Uniaxial Consolidation sh’ sv’

  10. K0 values during consolidation

  11. Determination of preconsolidation pressure Pc’

  12. StressCondition

  13. 1-D flow analysis

  14. Test Record: Undrained triaxial compression

  15. Shear induced pore pressure

  16. Mohr-Coulomb failure criterion

  17. Active failure slope expansion

  18. Slope stability analysis FS: Safety Factor ms: Sliding friction coefficient i: Slope angle (~2º) l*: normalized over pressure • Overpressure given by tests; • Sliding friction coefficient s; 0.03~0.12 (fs = 1.7 ~ 6.8º) • Assuming that s   = 0.424; • Normalized overpressure l*: 0.92 i

  19. Stress condition for active failure &Landslides

  20. i slope surface (a) slip line slip line slope expansion i (b) failure initiation MTD (c)

  21. Research Summary • Experimental simulations of sedimentation: • Ratio of sh’/sv’: ~0.6 • Overpressure: *= -0.27 ~ 0.707 increasing with depth • Shear failure criterion: t = stan(23º) • Shear strain may cause additional pore pressure to increase • The slope area is stable during sedimentation • Slope stability analysis reveals that the instability of the continental slope is more sensitive to active failure than landslides

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