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The Hydro-Mechanical behaviour of the Boom Clay: Hydro-Mechanical perturbation

The Hydro-Mechanical behaviour of the Boom Clay: Hydro-Mechanical perturbation during the Connecting Gallery excavation (Observations and predictions : project CLIPEX). Li xiangling. Outline. Main observations during the excavation of the CG Hydraulic perturbation

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The Hydro-Mechanical behaviour of the Boom Clay: Hydro-Mechanical perturbation

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  1. The Hydro-Mechanical behaviour of the Boom Clay: Hydro-Mechanical perturbation during the Connecting Gallery excavation (Observations and predictions : project CLIPEX) Li xiangling

  2. Outline • Main observations during the excavation of the CG • Hydraulic perturbation • Predictions of HM perturbation in the BC • 3D and 2D simulations • Comparison with in situ measurements (Pw) • Remaining key questions relating to the HM of BC • Constitutive laws development

  3. CLIPEX Instrumentation programme

  4. Main observations (1) Strong hydromechanical coupling • progressive increase • => Undrained contractant behaviour • - low KW ( 2 to 41012 m/s), • - high excavation rate ( 3 m/day). • sharp drop • => high decompression • - fracturation, • - volumetric dilation,

  5. Main observations (2) Strong hydromechanical coupling Large e => strong DPw

  6. Main observations (3) Strong hydromechanical coupling • Suction creation • => dilation • Sudden re-equilibrium with Pat • => opening of fractures Development of fractures around excavated gallery

  7. Main observations (4) Strong hydromechanical coupling Continual pw during liner installation => dilation, fracturing => Kw  Development of fractures around excavated gallery

  8. Main observations (5) Strong hydromechanical coupling Piezometers recordings • Unexpected extended disturbed zone : • EDZ > 60 m !! • => • fracturing effect ! • what else ?? Extensometer recording Development of fractures around excavated gallery

  9. Numerical predictions (EC project) • Partners : GEOCONTROL, UPM, G3S, and SCK • Numerical codes : FLAC 2D and FLAC 3D • - an explicit finite difference program • Constitutive laws • Main HM parameters used : - Mohr Coulomb  - Modified Cam Clay • Main hypotheses : • - Boom clay is considered as homogeneous and isotropic. • - gravity is considered in 3D simulation

  10. Numerical predictions - 3D (1) 43 m 108 m 98 m 60 m • 3D simulation : • 2nd shaft • starting chamber • CG • liners installations • gravity

  11. Numerical predictions - 3D (2) Pore pressure contours HDZ : 8-9 m HDZ :  20 m Influence zone of 2nd shaft limited  20 m

  12. Comparison : 3D prediction / in situ (1) The pw perturbations in situ are much higher than predicted! Horizontal plane

  13. Comparison : 3D prediction / in situ (2) The pw perturbations in situ are much higher than predicted! Vertical plane

  14. Numerical predictions - 2D (1) Modeling strategy Modeling zone

  15. Numerical predictions - 2D (2) Connecting Gallery Connecting Gallery TD TD Modeling procedure : 2) : draining of TD 1) : excavation TD (ND) 3) : excavation C.G (ND) C.G. TD

  16. Numerical predictions - 2D (3) s =4.5 MPa n s0 = -45 bar uw0 = 22 bar Boom clay 50 m x R Connecting Gallery Test Drift 0 y 60 m 20 m Modeling assumptions: • homogeneous, • isotropic • non gravity effect

  17. Comparison : 2D prediction / in situ (1) Tendency is predicted , but • HDZ > 60 m ! • DPw (measured) >> DPw (predicted) • classical laws (M-C, MMC)  CLIPEX GC Test Drift A2

  18. Comparison : 2D prediction / in situ (2) GC Test Drift Tendency is predicted , but • HDZ > 60 m ! • DPw (measured) >> DPw (predicted) • classical laws (M-C, MMC)  CLIPEX D2

  19. Comparison : 2D prediction / in situ (3) GC Test Drift Tendency is predicted , but • HDZ > 60 m ! • DPw (measured) >> DPw (predicted) • classical laws (M-C, MMC)  CLIPEX C2

  20. Remaining key questions relating to HM of BC (1) • Classical EP models ( M-C , MMC) • can't reproduce the extended HDZ • DPw (measured) >> DPw (predicted) Why ? • transition elasto -visco-plastic behaviour ? • anisotropy ( stress ) ? • fracturation effect ? • suction effect ? • HM coupling ( DKw with evvp for exemple ? ) Possible aspects to be considered ?

  21. Remaining key questions relating to HM of BC (2) Need a better elastoplastic constitutive law ? elastic zone : non DPw (hypothesis : isotropic ) plastic zone:DPw depends strongly on the ev Short term behaviors : M-C or MCC : sharp transition elastic / plastic

  22. Remaining key questions relating to HM of BC (3) An advanced EP model produce better DPw ! DK : Dafalias-Kaliakin BS 2B : Bubble model EP Parameters ! ( From J.D. Barnichon, 1998)

  23. Remaining key questions relating to HM of BC (4) Fracturation effect ? Constitutive law with damage + coupling (Kw, etc.)

  24. Remaining key questions relating to HM of BC (5) Skeleton behaviour = M Fluid behaviour = H viscosity Influence of time Fluid flow Fluid mass diffusion law = H(t) Time related behaviour (water flow and Viscosity of the skeleton )?

  25. Remaining key questions relating to HM of BC (6) • CLIPEX reveals the necessities to : • improve EP model , • take into account viscosity , • Consider suction effect , • And fracturation , • Better characterise in-situ properties : anisotropy ?

  26. Thank you very much !

  27. Numerical predictions - 3D (3) Pore pressure contours at the end of the excavation of 2nd shaft HDZ : about 10 m around the excavation

  28. Numerical predictions - 3D (4)

  29. CLIPEX Instrumentation programme

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