Hardening Soil model in geomechanical tool

  • Last Post 06 September 2018
Wasti posted this 05 September 2018

Hi everybody,

currently I´m trying to model a soil nailed wall at serviceability state and  I want to evaluate the role of nail bending stiffness. Thus I created a volume model, also simulating the excavation phases during the construction. Does anybody know how I can implement the "Hardening soil model" in Ansys?



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SandeepMedikonda posted this 05 September 2018

Hi Wasti,

  When you say implement, do you want to implement a custom material model by writing your own subroutine? Before doing that, I would recommend you to check out some of the geo-mechanical material models that are already available and might fit your needs:

  • Cam-clay
  • Mohr-Coulomb
  • Jointed Rock
  • Drucker-Prager Concrete
  • Menetrey-Willam

Please see this section of the help for some guidance on Geomechanical Material Models.



jjdoyle posted this 05 September 2018

We have a number of nonlinear material modeling options for geomechanic applications of soils, rock and aggregate materials. Refer to MAPDL online help Section 4.9 (Geomechanics) for more details.  There is also a simple example illustrating active/passive earth-pressure analysis in Section 48.6 of our Technology Demonstration Guide which might be a good place to start.   I am not aware of a worked out simulation for the specific "soil nailed wall" scenario.  We do support the inclusion of both smeared and discrete reinforcement, which might be useful here.



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Wasti posted this 05 September 2018

That´s the problem - I checked all geomechanical materials. The problem is the non linear material behaviour. soil has almost no linear range and also reacts different on un- and reloading. I thought about the use of hardening models with only a very small range of linear elasticity. But the next problem is that additionally the soil stiffness depends on the S3 stress state. This means withi increasing depth you have different stress strain relations, means a different curve...

jjdoyle posted this 05 September 2018

Yes that is correct.  All the soil models referenced above have yield surface formulas that are dependent on hydrostatic pressure with very little strength in tension. So the greater the compression (S3) the stronger the material becomes (just like soils).  Isn't the purpose of these "nails" to introducing compression and thereby stabilize the material?

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Wasti posted this 06 September 2018

No, you mean prestressed anchors. But the working of the nails is discussed controversely. The most reasonable explanation is that the nails increase the soil´s shear strength. A problem of all the ansys soil models is that they describe the yield surface. But for the modelling of reinforced slopes and excavation stages more advanced material models like Hardening soil model or the hardenings soil model with small strains or a hypoplastical model should be used, as they refer to the nonlinear stiffness. Other codes like Plaxis or Abaqus implemented the models and I foundone thesis of a german guy who developed a user hypoplastical user material. But maybe somebody knows another possibiltiy to implement the hardening soil model as described in (https://www.plaxis.com/?plaxis_download=2D-3-Material-Models.pdf) into ansys?