I am looking at a problem where heat treated ground is undergoing desiccation and volume reduction.
Is there a soil behaviour model that can model the deformation (settlement) of the ground with respect to its moisture content? Can this be coupled with a time dependant thermal analysis? From my reading so far, the thermal deformation seems to be linked to the expansion coefficient rather than any water driven off by heat.
Do thermal effects alter the moisture content?
Which behaviour model do I need to adopt to ensure the moisture content affect deformation (shrinking and swelling)?
Many thanks
Scot
Dear Scot,
Currently, the only mechanism allowing to simulate this is through evaporation, with vapour diffusion.
In thermal tabsheet, the user can put value for diffusivity and enables vapour flux to simulate moisture loss by temperature gradient. You can also look at the link to the paper from ECSMGE-2019, section 4: pure.tudelft.nl/.../0499_ecsmge_2019_Bui_Casarella_DiDonna_Brinkgreve_final.pdfNote that the simulation in section 4 uses a user-defined flow model, however, the vapour diffusion is already available for all models.
In general, you can start with a simple Linear Elastic or Mohr-Coulomb model to see the behaviour. When heating, enabled vapour diffusion reduces saturation, so suction and mean effective stress (compressive) is increased.
So, the expected following phenomena should be: elastic compression (shrinkage), soil thermal expansion, and no increasing plastic shear deformation. If soil thermal expansion is small compared to the elastic shrinkage, then some small ground settlement should be noticed.
As always, the exact behaviour depends on the parameters used in the model.
Answer Verified By: Scot Francis
Hi Stefanos. I have the opportunity to look at this in some more detail now and have 2 main questions. Thankyou for your detailed response.
Firstly, the purpose here is regarding ground settlement once some high moisture content clay is heated. I can use the vapour flux to do this and define a temperature at which the water is driven off, which should then reduce the volume of the clays. I consider this volume contraction will be significantly greater than the thermal expansion, so a net reduction in volume should follow.
Also, I am not interested in the strength of the material with respect to the thermal effects, therefore I can use a linear elastic model, as all volume contraction will be in the elastic domain.
So my query is: If I have a thermally affected soil volume with a very low (or zero) moisture content, and an impermeable barrier (sheet piles) between this and some other soils which have a higher moisture content and are less thermally affected, I would expect there to be some significant suction and rebalance of moisture content as the desiccated soils pull moisture out of the local high moisture content soils. This would cause volume loss in the soil volume that was not directly thermally affected.
Can these effects also be modelled using the same approach?
Can this be done on a time-dependant analysis?
Many thanks for your kind attention so far,
About your query: moisture is transferred by two mechanisms: water flow (unsaturated Darcy's law) and vapour flux created by temperature change (more precisely temperature gradient). So, even if the wet part is thermally inactive (no vapour created), the water pressure gradient would bring water from low suction to high suction zone.
Many thanks again Stefanos. I will build the model over this coming week once I receive the information, and will run it as outlined above to determine if it behaves in the manner that I would anticipate. I will share the model once I am in a position to validate its reliability, or if I have some questions on the advection component /the model does not behave as expected. Much appreciated.
You are welcome. Looking forward to hearing from you.