It is observed in simulations of excavation projects using the Hardening Soil model (or HS small model) that the soil below the bottom of the excavation behaves less stiff than in reality. The reason is that the stiffness of soil is stress-dependent and excavation releases the stress on top, however, in reality, the stiffness will not reduce so much due to the pre-consolidation stress. Therefore, in the GHS model (generalized hardening soil model) the stress dependency formulation of the Hardening Soil small model has been altered in order to account for the pre-consolidation stress. The Generalized Hardening Soil model (GHS) is a more modular version of the original Hardening Soil small model. It has several switches which allow the users to change the configurations of strain and stress dependency.

 

With the release of PLAXIS 2D/3D CONNECT Edition V20 Update 1 (January 2020), the PLAXIS User Defined Soil models are delivered with the PLAXIS installation. When enabling the Geotechnical SELECT Entitlement [GSE] when starting the PLAXIS application, this model becomes available in the Parameters tab when selecting "User-defined" for the Material model.

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November 2017: dynamic calculations in 2D 2017.01

Known issue ID: SW-22102

The latest version of Generalised Hardening Soil model (GHS), version 2016.0.0.0 dated March 13, 2017, does not work for dynamic calculations in PLAXIS 2D 2017.01. This is related to improvements in the calculation kernel concerning the critical time step calculations.
For now, if you have a dynamic calculation using the GHS model, you are advised to downgrade to PLAXIS 2D 2017.00 and then you can use the mentioned version of the GHS model without any problems.

The issue is now resolved in PLAXIS 2D 2018.00 (March 2018).

November 2017: Matsuoka-Nakai failure criterion not available

Known issue ID: SW-22582

In the parameter list for the GHS soil properties, there is an option to select between these two failure criteria: Mohr-Coulomb and Matsuoka-Nakai. However, in the constitutive model, only the Mohr-Coulomb failure criterion is actually available. Please keep this parameter value for failure (0:MC or 1:M-N) to 0 [zero] to ensure clear model definition and avoid confusion when checking the model at a later stage of your project.

November 2016: Free field elements

Known issue ID: SW-11318 [Solved]

An issue with the GHS model in combination with the free field elements was solved in GHS version 2016.0.0.0 (March 2017) and tested/verified in PLAXIS 2D 2017.00.

When using an older version of the Generalized Hardening Soil (GHS) user-defined soil model in soil elements adjacent to free field elements in a PLAXIS Dynamics calculation, the behaviour of the free field elements can show random behaviour. This could lead to incorrect behaviour of the free-field element (e.g. taking the incorrect stiffness value) or the calculation gives an error and stops abnormally.

For older versions, please define a small soil column adjacent to the free field elements or compliant base elements using a different soil model, for instance, the HSsmall model, or a Mohr-Coulomb model with equivalent stiffness.

September 2016: Solved issue with more than one GHS material set

Known issue ID: SW-5362 [Solved]

In the implementation of the Generalized Hardening Soil (GHS) model version 2014.223.0.0 (March 2014) the internal parameter determination is only stored for one material dataset at the beginning of a calculation phase. This means that when having more than one material dataset using the Generalized Hardening Soil model, these internal parameters for the stiffness behaviour will only use the parameters from one material dataset, and this gives incorrect behaviour for all the other material datasets using the GHS model.

This issue is now solved with GHS model version 2016.0.0.0 (April 2016), and is now available after thorough checking.

June 2016: State parameters

Known issue ID: SW-7722 [Solved]

State parameters: the state parameters for the GHS model are available under Stresses > State parameters > User defined parameters. The state parameter names for this user defined soil model all start with [HSSmall]. However, the shown captions for the the state parameters for the Generalized Hardening Soil (GHS) model version 2014.223.0.0 (March 2014) are not correct. It appears that some of the parameters show results that correspond to another parameter and for some other parameters the selected option gives different state parameter value in tables/plots point, and not for the one selected.
Example: selecting [HSSmall] Gact actually shows G/Gur.

The issue is now resolved in GHS Version 2016.0.0.0 (March 2017)