Undrained modelling in FE analysis

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Undrained modelling in FE analysis

• Why it matters

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Nicoll Highway, Singapore
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Nicoll Highway, Singapore
Public Inquiry concluded that failure to model
undrained behaviour correctly in FE was a major
cause of the disaster.
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People who dont understand this should not be
doing geotechnical FE
t (sv sh)/2
Incorrect undrained strength
Method A
Mohr-Coulomb no dilation
Method B
cu
K0
t/s sinf
Correct undrained stress path
s (sv sh)/2
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On 20 April 2004 9th level strut, 10th level
excavation BP00.1
1st level strut
2nd level strut
3rd level strut
4th level strut
5th level strut
6th level strut
7th level strut
8th level strut
9th level strut
72.4mPD
5 10m
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Double the displacement and bending moment
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Five methods of analysing undrained soils
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Drained, undrained, consolidating, steady state,
no water
Drained
Undrained
Drained
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Drained, undrained, consolidating, steady state,
no water
Drained
Consolidating

• Drained zones form a fixed head boundary to
  consolidating zones

Drained
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Drained, undrained, consolidating, steady state,
no water
Drained
Undrained

• Drained zones form a fixed head boundary to
  consolidating zones
• but not to undrained zones.

Drained
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Undrained behaviour in FREW
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Undrained behaviour in FREW
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Undrained behaviour in FREW
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Undrained behaviour in FREW
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Undrained behaviour in FREW
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Undrained behaviour in FREW
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Undrained stress path in FREW
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