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Problem with Geostatic Step (Coupled Pore Fluid and Diffusion Analysis)

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typples

Geotechnical
Oct 21, 2019
1
I'm having difficulty getting my Geostatic Step to converge for 1km x 1km block of Westerly Granite. I'm working on a 3D toy model for up-scaling later.

Material: Elastic: E = 3.75e10; PoissonRatio = 0.25 Permeability : k=0.000864 (m/day); void ratio = 0.01 Porous Bulk Moduli: grains= 4.2e10 (Pa) ; fluid = 2.2e9 (Pa)

I define BCs: BC1 as u1=u2=u3=0 for the bottom surface. BC2 as u1=u2 = 0 for sides BC3 as Pore Pressure = 0 for surface (drained conditions)

Predefined Field : VR = 0.01

First step: Apply Body Force Load = density x gravity = -2650 x 10

I've tried different Automatic Stepping at very small increments with very large max displacement changes. In the .msg file I get very small Average Force values compared to the Largest Residual Force value, and so thus the first residual tolerance is likely not converging. Mesh size does not appear to have a large effect either. .inp file attached.
 
 https://files.engineering.com/getfile.aspx?folder=801f197d-bc61-48b6-817c-a2d5d5306e30&file=WGtoy.inp
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