Consolidation Analysis in Plaxis

Dear all,

First, thank you for your replies and kudos to PLAXIS for starting a forum like this.

When calculating consolidation using conventional methods (by using Cc and Cs coefficients, together with the foundation stress) we can easily predict the settlement of foundations under service loads. To overcome settlement, soil improvement or deep foundation can be utilised.

In PLAXIS 2D we can use soft soil to predict the settlement under the structure foundations by choosing staged construction, minimum degree of consolidation and minimum pore water pressure options. By using one of these options, generally, the calculated consolidation settlement exceeds the obtained calculation from the numerical analysis (this is my own opinion).

In practice, most of the times deep clay layers are encountered, thus different compression indexes can be obtained and the compressible layers can be obtained by finding the effective depth of the applied stress.

In plaxis, we can model these by choosing different soil layers with different characteristics. I do not think that the drainage condition (drained and undrained) affects the consolidation calculation in plaxis. It is the permeability coefficients that determine the process.

  1. What are the recommendations when performing consolidation analysis? In order to get the conventionally predicted settlement values.
  2. What are the recommendations regarding the permeability coefficients (kx & ky) and the change of permeability (ck)?
  3. What is the more correct consolidation analysis option? Analysis of building foundations.
  4. Is there any example, regarding this topic?

Any other recommendation will be highly appreciated.

Thank You.

  • Dear Abdirahman,

    Thank you for your kind words. With the Wiki and Forum, we hope to allow for even more information about PLAXIS and SOILVISION to be transferred to the users.

    Back to your question, most aspects mentioned highly depend on the modelling techniques and engineering judgement.

    You are correct to mention that in a consolidation analysis the calculation is mostly driven by the permeabilities of the materials included. 

    To be able to get accurate results, firstly, you need to have the correct constitutive model to capture the soil behaviour. As you probably already know, if you have any laboratory data to calibrate the parameters of the numerical model then the results will be closer to reality.

    We do not really have any recommendations for material parameters as there is a vast number of soils with different properties all over the world that makes it very difficult to create such databases. Typically the user should get all the available data from laboratory tests, previous records of nearby projects, engineering judgment, etc. to be able to run the analysis.

    With consolidation, it is possible to include a staged construction loading type, therefore building foundations can be easily performed following this approach. The time interval can be defined following the (real) construction planning.

    You can find all the available examples online in the Wiki pages. For instance:
    https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/46099/staged-construction-of-embankments-on-soft-soil-using-plaxis

    If you have a specific model in which you have problems, please submit a service request. Then, one of our support engineers can help you in detail:
    https://apps.bentley.com/srmanager/ProductSupport