NON

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NON LINEAR ELASTIC SMALL STRAIN STIFNESS MODEL
FOR CRISPbySooriyakumaranSOUTH BANK
UNIVERSITY21 09 - 01
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INTRODUCTION

• This numerical soil model was developed by
  Jardine et al. (1986) of IC.
• The model is based on shear moduli G and bulk
  moduli K.
• Soil properties used for the analysis was
  obtained from book by Potts, D. M. and Lidja, Z.

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EMPIRICAL RELATIONSHIP

• Stiffness Gsec and Ksec are obtained
• from following empirical equation

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EMPIRICAL RELATIONSHIP

• Where A, B, C, ?, ?, R, S, T, ? and ? are
• material Constants.
• Ed Deviatoric strain ?v Volumetric strain
• And given the following equation.

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EMPIRICAL RELATIONSHIP

• Tangential shear and bulk modulus are
• obtained by differentiating the above equation
• and is given by

These eqns are used in the programming
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TESTING OF THE MODEL
The model is tested by modelling simple Triaxial
test. The graphs below show the secant shear and
bulk modulus Against respective strains obtained
from the above analysis.
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APPLICATION

• A shallow tunnel was modelled and analysed using
• this model. The tunnel diameter is 5m and
  symmetry
• was assumed. Mesh was modelled for 3Z to right of
  the
• tunnel from the axis and 2z below the axis. Z is
  depth
• of axis of the tunnel from surface, which is
  taken as 20m.

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Finite Element Mesh

• Figures below show the mesh layout and
• excavated mesh layout. Excavation is
• modelled by removing elements.

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DISCUSSION

• The graph below shows the settlement
• profile for various increments.

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DISCUSSION

• Figure below shows the settlement profile
• Obtained from three analysis using this
• model , Gunn small strain model and
• elastic model.

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DISCUSSION

• The settlement profile obtained from the
• above analysis is compared with Pecks error
• curve which is obtained using following eqn

The surface settlement profiles obtained from F.E
and Pecks Curve are shown below.
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CONCLUSION

• The results obtained are sensible and encouraging
  compare with the other models.
• There are few defects in the model especially
  limitation of the model.
• This model is developed only for elastic region
  but actual soil behaviour is not like that.
• Number of parameters to be obtained are more.