PFV compressibility in undrained triaxial test

Asked by Christian Jakob on 2014-08-25

Hi,

I want to get the pore pressure of a saturated soil sample in an undrained triaxial test when the sample volume is decreasing.

...
TriaxialStressController(thickness=0,stressMask=7,internalCompaction=False,label='triax')
...

 triax.goal1 = 35000
 triax.goal2 = 35000
 triax.goal3 = 70000
 triax.wall_back_activated = False
...
 flow.viscosity = 1.3e-3
 flow.fluidBulkModulus = 2e9
 flow.bndCondValue=[0,0,0,0,0,0]
 flow.bndCondIsPressure=[0,0,0,0,0,0]
...

For one of my simulations a decrease of ca. 1,8 % in porosity (=-dV/V) is obtained. When I calculate corresponding pressure increase I get

dp = K*(-dV/V) = 2e9*0.018 = 36000000 Pa

But the output from PFV shows maximum average pressures around of 16 Pa (not MPa!). As long as I use SI units the output of flow.averagePressure() should be Pa, right?

So is there a problem in the code or did I miss something in the compressibility option of PFV?

regards,

christian

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2014-08-25
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