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Case Study Stability of an earthdam Stéphane Commend – Françoise Geiser

Case Study Stability of an earthdam Stéphane Commend – Françoise Geiser GeoMod consulting engineers www.geomod.ch. Summary Settlement analysis of the existing earthdam Global stability analysis Stability analysis of the earthdam (= local) Simplified seismic analysis Work in progress.

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Case Study Stability of an earthdam Stéphane Commend – Françoise Geiser

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  1. Case Study Stability of an earthdam Stéphane Commend – Françoise Geiser GeoMod consulting engineers www.geomod.ch

  2. Summary • Settlement analysis of the existing earthdam • Global stability analysis • Stability analysis of the earthdam (= local) • Simplified seismic analysis • Work in progress

  3. Summary • Settlement analysis of the existing earthdam • Global stability analysis • Stability analysis of the earthdam (= local) • Simplified seismic analysis • Work in progress

  4. existing earthdam 2D cut schematic position of the future material deposit Dam and material deposit overview

  5. Existing earthdam

  6. Access road

  7. Material deposit. Step 1

  8. Material deposit. Step 2 (provisory)

  9. Material deposit (final configuration) Vcalc = 1’643’000 m3

  10. Water basin Existing earthdam Material deposit (final configuration)

  11. about 500 m future material deposit earthdam 25 m Dam and material deposit 2D cut

  12. Asphalt Pore pressure, with cracked asphalt (K = 1e-4 m/s)

  13. Settlement = 3.0 cm Absolute displacements, 2D model T = 6: maximal displacement, with provisory deposit

  14. Initial position Deformed mesh (x 20), 2D model T = 6: maximal displacement, with provisory deposit

  15. Plant Earth dam

  16. Plant Earthdam

  17. Plant Earthdam Absolute displacements, 3D model

  18. Earthdam Settlement = 0.5 cm Absolute displacements, 3D model

  19. B A Déplacement absolu [m] T Evolution of the settlements for different models

  20. Summary • Settlement analysis of the existing earthdam • Global stability analysis • Stability analysis of the earthdam (= local) • Simplified seismic analysis • Work in progress

  21. Global stability analysis in Z_Soil (one method) • Compute problem with given ci and fi in all materials • Divide ci and tan(fi) by a factor 1.0, 1.1, 1.2, ... • … recompute until failure occurs

  22. SF = 1.50 Global safety factor, 2D analysis

  23. SF = ??? 2 3 SF = 1.70 1 Global safety factor, 3D analysis

  24. Summary • Settlement analysis of the existing earthdam • Global stability analysis • Stability analysis of the earthdam (= local) • Simplified seismic analysis • Work in progress

  25. Summary • Settlement analysis of the existing earthdam • Global stability analysis • Stability analysis of the earthdam (= local) • Simplified seismic analysis • Work in progress

  26. Introduction • 16 m high earth dam is of class III (SFOE guidelines) • => Replacement forces analysis can be conducted • Global horiz. acceleration: log(ah) = 0.26 IMSK + 0.19 in cm/s2 • IMSK from seismic intensity maps, Treturn = 1’000 years • Here, ah = 1.65 cm/s2 = 0.17·g • av = 2/3·ah = 0.11·g (both upwards and (here) downwards)

  27. ah = 0.17 g av = 0.11 g

  28. SF = 1.61

  29. Summary • Settlement analysis of the existing earthdam • Global stability analysis • Stability analysis of the earthdam (= local) • Simplified seismic analysis • Work in progress

  30. Work in progress • Influence of rain inflow on stability of slopes • Steady state and transient • 2D and 3D

  31. Water table without rain inflow on the material deposit (steady-state analysis)

  32. SF = 1.50 Global safety factor, 2D analysis

  33. raininflow: 2 cm / day Water table with rain inflow on the material deposit (steady-state analysis)

  34. raininflow: 2 cm / day SF = 1.20 Global stability study after rain inflow

  35. Châtelard deposit. 3D influence of rain inflow. Pore pressures, dry case (no rain)

  36. Châtelard deposit. 3D influence of rain inflow. Dry case Progression of displacements with increasing SF

  37. Châtelard deposit. 3D influence of rain inflow. Dry case Progression of displacements with increasing SF

  38. Châtelard deposit. 3D influence of rain inflow. Dry case Progression of displacements with increasing SF

  39. Châtelard deposit. 3D influence of rain inflow. Dry case Progression of displacements with increasing SF

  40. Châtelard deposit. 3D influence of rain inflow. Dry case Progression of displacements with increasing SF

  41. Châtelard deposit. 3D influence of rain inflow. Dry case Progression of displacements with increasing SF

  42. Châtelard deposit. 3D influence of rain inflow. Dry case Progression of displacements with increasing SF

  43. Châtelard deposit. 3D influence of rain inflow. Dry case Progression of displacements with increasing SF

  44. Châtelard deposit. 3D influence of rain inflow. Dry case Mechanism associated with diverged step. Global safety factor = 3.00

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