Geogrid Structural Element and Groundwater Flow in FLAC3D

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Hi everyone, @itascan @dafo407_itasca @itasca @ddegagne @dblanksma

I am modeling a reinforced soil wall in FLAC3D where geogrid structural elements are used as reinforcement. In my study, the reinforcement should not act as a hydraulic barrier, meaning groundwater should be able to pass through the geogrid while it provides only mechanical reinforcement.

I am creating the geogrids using the following commands:

struct geogrid create by-face internal group 'geogrids=geogrid1' ...
    range group 'layer1A:layer1B'

;struct geogrid property isotropic=(5.39e8,0.33) thick=5e-3 ...
;     coupling-stiffness=1e6 coupling-cohesion=0 ...
;     coupling-friction=30 slide on range group 'geogrid1'

My questions are:

  1. Is the geogrid structural element permeable by default, i.e., does it allow groundwater/pore water to pass through it without affecting the fluid flow?
  2. Or do I need to use any additional command or setting to make the geogrid permeable?
  3. Does the geogrid participate only in the mechanical calculation, while the fluid flow is solved entirely through the surrounding zones?
  4. Is there any section of the FLAC3D documentation or any example model that discusses the hydraulic behavior of geogrid structural elements?

Any clarification or references would be greatly appreciated.

Thank you!