The HydroMechanical behaviour of the Boom Clay:

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

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CLIPEX Instrumentation programme
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Main observations (1)
Strong hydromechanical coupling

• progressive increase
• gt Undrained contractant behaviour
• - low KW (? 2 to 4?10?12 m/s),
• - high excavation rate (? 3 m/day).
• sharp drop
• gt high decompression
• - fracturation,
• - volumetric dilation,

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Main observations (2)
Strong hydromechanical coupling
Large e gt strong DPw
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Main observations (3)
Strong hydromechanical coupling

• Suction creation
• gt dilation
• Sudden re-equilibrium with Pat
• gt opening of fractures

Development of fractures around excavated gallery
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Main observations (4)
Strong hydromechanical coupling
Continual pw ? during liner installation
gt dilation, fracturing gt Kw ?
Development of fractures around excavated gallery
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Main observations (5)
Strong hydromechanical coupling
Piezometers recordings

• Unexpected extended disturbed zone
• EDZ gt 60 m !!
• gt
• fracturing effect !
• what else ??

Extensometer recording
Development of fractures around excavated gallery
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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

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Numerical predictions - 3D (1)

• 3D simulation
• 2nd shaft
• starting chamber
• CG
• liners installations
• gravity

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Numerical predictions - 3D (2)
Pore pressure contours
HDZ 8-9 m
HDZ ? 20 m
Influence zone of 2nd shaft limited ? 20 m
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Comparison 3D prediction / in situ (1)
The pw perturbations in situ are much higher than
predicted!
Horizontal plane
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Comparison 3D prediction / in situ (2)
The pw perturbations in situ are much higher than
predicted!
Vertical plane
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Numerical predictions - 2D (1)
Modeling strategy
Modeling zone
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Numerical predictions - 2D (2)
Modeling procedure
2) draining of TD
1) excavation TD (ND)
3) excavation C.G (ND)
TD
C.G.
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Numerical predictions - 2D (3)
Modeling assumptions

• homogeneous,
• isotropic
• non gravity effect

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Comparison 2D prediction / in situ (1)
Tendency is predicted , but

• HDZ gt 60 m !
• DPw (measured) gtgt DPw (predicted)
• classical laws (M-C, MMC) ?

CLIPEX
GC
Test Drift
A2
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Comparison 2D prediction / in situ (2)
Tendency is predicted , but

• HDZ gt 60 m !
• DPw (measured) gtgt DPw (predicted)
• classical laws (M-C, MMC) ?

CLIPEX
D2
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Comparison 2D prediction / in situ (3)
Tendency is predicted , but

• HDZ gt 60 m !
• DPw (measured) gtgt DPw (predicted)
• classical laws (M-C, MMC) ?

CLIPEX
C2
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Remaining key questions relating to HM of BC (1)

• Classical EP models ( M-C , MMC)
• can't reproduce the extended HDZ
• DPw (measured) gtgt 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 ?
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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
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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)
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Remaining key questions relating to HM of BC (4)
Fracturation effect ?
Constitutive law with damage coupling (Kw,
etc.)
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Remaining key questions relating to HM of BC (5)
Time related behaviour (water flow and Viscosity
of the skeleton )?
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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 ?

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Thank you very much !
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Numerical predictions - 3D (3)
Pore pressure contours at the end of the
excavation of 2nd shaft
HDZ about 10 m around the excavation
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Numerical predictions - 3D (4)
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CLIPEX Instrumentation programme