Civil Engineering Analysis and Modelling (CIVL3140)

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Drained:Water is assumed to immediately flow out upon loading and therefore no pore pressure are built up. This is appropriate when

Permeability is high;Rate of loading is low;Short term behaviour is not interest for problem considered.

Undrained:No water movement takes place and therefore pore pressure are built up. This is appropriate when:

Permeability is low and rate of loading is high;Short term behaviour has to be assessed.

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Load – water is squeezed out over long time

3

time

settl

emen

tGL

saturated clay

q kPa

Au

’

u

’

q

Mohr-Coulomb parameters in terms of effective stress

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Mohr-Coulomb parameters in terms of total stress (only undrained condition)

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Method A: Analysis in terms of effective stressType of material: undrainedEffective strength parameter c’, ’, ’ Effective stiffness parameter E50’, ’

Method B: Analysis in terms of effective stressType of material: undrainedTotal strength parameter c=cu =0, =0Effective stiffness parameter E50’, ’

Method C (Analysis in terms of total stress)Type of material: drainedTotal strength parameters c=cu =0, =0Total stiffness parameters Eu, u=0.495

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Single set of parameters in terms of effective stress;Realistic prediction of pore pressures;The undrained analysis can be followed by a consolidation analysis;Cu is consequence of the model, not an input parameter.

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Undrained A: limitation of MC model

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9

Bending momentUndrained A (MC) Undrained B (MC)

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Parameters in terms of total stress and effective stress;Prediction of pore pressures;(generally unrealistic);The undrained analysis should not be followed by a consolidation analysis (pore pressure unrealistic)Cu is an input parameter.

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Parameters in terms of total stressNo prediction of pore pressure.The undrained analysis cannot be followed by a consolidation analysis.Cu is an input parameter.

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Method ARecommended, but be careful with MC model;Soil behaviour is always governed by effective stresses;Increase of shear strength during consolidation;Essential for exploiting advanced soil model, such as hardening soil model;

Method BOnly when no information on effective strength parameters is available;Maybe a safer choice than Method A;

Method CNot recommended;No information on excess pore pressure.

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Hardening soil model

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