# Permeability values and model solve command

**URL:** <https://forum.itascainternational.com/t/permeability-values-and-model-solve-command/1793>\
**Category:** FLAC3D\
**Created:** [November 8, 2024, 5:56pm UTC](https://forum.itascainternational.com/t/permeability-values-and-model-solve-command/1793 "2024-11-08T17:56:07Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![sowmyaramanis](https://avatars.discourse-cdn.com/v4/letter/s/839c29/32.png) [@sowmyaramanis](https://forum.itascainternational.com/u/sowmyaramanis)\
**Post date:** [November 8, 2024, 5:56pm UTC](https://forum.itascainternational.com/t/permeability-values-and-model-solve-command/1793/1 "2024-11-08T17:56:07Z")

</div>

1. In general, the permeability is soil’s property and will vary for different soils. But in flac3D, the permeability is fluid’s property. Then how will I assign different permeability values for layered soil?
2. In commands like model solve or model solve fluid, on what basis do we decide the solving value like 1e-4 etc.

Kindly help me

---

<div class="post-metadata">

**Author:** ![dblanksma](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@dblanksma](https://forum.itascainternational.com/u/dblanksma)\
**Post date:** [November 11, 2024, 8:20pm UTC](https://forum.itascainternational.com/t/permeability-values-and-model-solve-command/1793/2 "2024-11-11T20:20:14Z")

</div>

Hello @sowmyaramanis,

I may be misunderstanding your question. But, (1) the permeability assignment is a zone (material) property. Maybe the fact that it is assigned by **zone fluid property** command is confusing.

(2) The limit to which the model is considered to be in equilibrium is the user’s choice. Some simple models may achieve mechanical (or fluid) equilibrium with a convergence criteria of 1e-4, other more complicated models may need a smaller convergence value. A great place to learn about solving to equilibrium is provided here - [Reaching Equilibrium — Itasca Software 9.0 documentation](https://docs.itascacg.com/itasca900/flac3d/docproject/source/modeling/problemsolving/equilibrium.html?node2279)