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getCapillaryStress

Asked by Amiya Prakash Das

Hi

When i am using this getCapillaryStress utility function, i am getting mean capillary stress in order of 10^-9 kPa. So, i calculated my deviatoric stress from the triaxial stress recorder and getStress, so i nearly got them as same (but for each iteration getStress gave me higher deviatoric stress which differed by an order of 10^-3). For all my cases (constant suction triaxial) i got higher deviatoric stress for wet cases in comparison to the dry case, but my capillary stresses where very less and i checked few of the published papers, where their capillary stress was much more higher in order of 4 - 5 kPa.

So, i don't understand why inspite of getting higher deviatoric stress for wet cases with respect to dry case, my capillary stresses are still so less.

Thanks
Amiya

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Jérôme Duriez (jduriez) said : 		#1

Hi,

I did not completely understand your concern, but here are few points:

In "wet simulations" you should get the equality total stress = contact stress + capillary stress, where:
- the total stress are measured from the boundaries, e.g. using triaxial engines
- the contact stress is the stress contribution from ("dry") contact forces = getStress()
- the capillary stress is the stress contribution from capillary forces = getCapillaryStress()

As an *important* note, the two get*Stress() functions require the sample volume to be passed as an argument, with getStress having a more user friendly default behavior (picking a correct value if the user forgets to pass one) in this regard, though

If you do not get this equality, it means you're not using correctly the functions, or your simulation is not quasi-static.

If your concern is that you have very low capillary stress, the answer is still the same as in previous questions: you have too big particles (for classical surface tension values). Play with small particle sizes, as unsaturated experimentalists consider fine soils and not gravel.

If you wish, you may actually also try to construct the Soil Water Characteristic Curve of your numerical sample (in this pendular regime) to check if you have "significant" capillary pressure * saturation product values. If not, it means again your particle sizes are too big.

Jerome

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Amiya Prakash Das (amiya0703) said : 		#2

Thanks Jerome for your answer, as you pointed out the equality of total stress, i am getting that value equal. How far my particle sizes are concerned, they are very similar to what other researchers have used and other parameters are same as their. My problem is with the stress value i am getting, in my simulation contact force and capillary forces are of same order. But when i am calculating the stresses, the difference in too large and order of capillary stresses in very small (10^-9). But, my peak stress value for dry case and wet case differs my around 15 kPa. So, i am only concerned about small capillary stress contributing so much to peak stress. I read few papers in which the capillary stress was in order of 4-5 kPa. So, i am bit concerned about the values i am getting.

Thanks
Amiya

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Launchpad Janitor (janitor) said : 		#3

This question was expired because it remained in the 'Open' state without activity for the last 15 days.