Possible incorrect cohesion increment for Soft Soil and Soft Soil creep

ApplicationPLAXIS 2D
Issue status✔ Solved
First Affected VersionPLAXIS 2D 2011.00
PLAXIS 3D 2012.00
Found in VersionPLAXIS 2D 2011.00
PLAXIS 3D 2012.00
Fixed and Released in VersionPLAXIS 3D 2017.00
Issue #22391
Date created15 January 2015
Date modified09 October 2017

Problem description

When defining a soil dataset using the Soft Soil or Soft Soil Creep model in the material database, only the strength parameters cohesion cref, friction angle φ and dilatancy angle ψ are available as input fields. Other soil models, e.g. Mohr Coulomb and Hardening Soil, allow for an additional strength parameter to be defined: a cohesion that increments in depth: cinc
Although this input field is not present for the Soft Soil and Soft Soil Creep model, in PLAXIS 2D 2017.00 (or earlier) and PLAXIS 3D 2016 (or earlier) this strength parameter is still taken into account in the constitutive soil model’s behaviour.

In most cases, this is not a problem: the value for cinc is initialized at a zero value, i.e. no cohesion increment with depth. However, when changing an existing material dataset to the Soft Soil or Soft Soil Creep model from a soil model that has this input field available and this cinc has a value, this cinc value is internally remembered in PLAXIS 2D and PLAXIS 3D 2016 (or earlier) and used during the calculation when changing to the Soft Soil or Soft Soil Creep model.


First a soil dataset with the Mohr-Coulomb model was defined with a cohesion of cref = 14.5 kN/m2 and cinc = 0.5 kN/m2/m. After that the soil model for this dataset was changed from Mohr-Coulomb to Soft Soil Creep. Internally, the program will still remember the cohesion value cref = 14.5 kN/m2 and cinc = 0.5 kN/m2/m. The value for the cohesion cref is clearly available as an input field, but the user cannot see or change the value for the cohesion increment cinc value for the Soft Soil Creep model.

Currently this cinc value cannot be reviewed in the material database in the Input program. Only after the calculation, in the results, one can check the value for the current cohesion. To see this, go to Stresses > State parameters > c
Based on the values in each cluster, one may see if it is a constant value (i.e. cinc = 0 kN/m2/m), or the cohesion value for this Soft Soil or Soft Soil Creep material changes in depth (i.e. cinc ≠ 0 kN/m2/m).


Since PLAXIS 2D 2017.01 and PLAXIS 3D 2017, the cinc value will always be reset to 0 (zero) when using Soft Soil and Soft Soil Creep.

For older versions of PLAXIS 2D (2017.00 or earlier) and PLAXIS 3D (2016.02 or earlier), please review the cohesion value in the results by inspecting the plot and/or tables for all used Soft Soil and Soft Soil Creep material datasets via the menu item Stresses > State parameters > c and inspect if the expected cohesion value is used.

When unexpectedly a value for cinc has been used in the calculation, the safest way to solve this is to: