Advanced Soil L7


How does elasto-plasticity look in σ-ε space?

This is 1D elasto-plasticity

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how about in 2D

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How does the yield locus change expanding/contract

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What is the initial yield locus?

The boundary of the elastic region.

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What happens to the locus in final state?

The state of failure is the final yield locus which no longer expands/contracts

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How is the yield locus defined in 3d?

The yield locus becmes a yield surface

Elastic behaviour when this is < 0

Impossible stress when > 0

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What is the plastic potential surf?

A surface which defines the direction of plastic straining on yield surface

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What is associated plasticity + flow rule?

Flow rule: the vector of total plastic strain normal to plastic potential surface

Associated plasticity : if YS and PS coincide, where F=P

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how is behaviour below Roscoe surf?

Elastic. On the yield surface, (Roscoe, Hvorslev, or tension failure), is elasto-plastic

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How is CS reached on 'wet' side?

Strain-hardening shown by expansion of the envelope

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How is CS reached on 'dry side' of CS?

The envelope contracts in on the 'dry' side, strain-softening

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How do the surfaces look in J-p’-theta?

deviatoric plane is circular

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How does the MCC model develop?

 Adopt ellipse

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What are the MCC equations?

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How is the deviatoric plane for the MCC?


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Is the MCC surface different to Roscoe/Hvorslev?

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How it looks in 3D space

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How is diff in vol strain (pl) found?

Determining total vol strain:

v= N-λlnp'

differentiating: dv/dp' = -λ/p'

Determining elastic: v= vk-klnp', dv/dp' = -k/p'

so the sum -k/v*dp'/p + λ/v*dp'/p' = de,pvol

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How is diff in volumetric strain (el) found?

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Features of MCC model

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Why can MCC be unconservative?

It overpredicts the strength in deviatoric plane outside triaxial compression 

solution: Use Mohr-Columb in expression

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Why is the MCC bad at modelling dry side?

It overpredicts strength of the highly overconsolidated clay

Introduce Hvorslev and ensure flow rule at critical state

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Why else is MCC unconservative?

Overpredicts side of elastic region - couple MCC with a small strain stiffness model

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What is formula for incremental vol strain?

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What is formula for incremental deviatoric strain?

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