# Application of the Dafalias Model

**URL:** <https://forum.itascainternational.com/t/application-of-the-dafalias-model/1169>\
**Category:** FLAC3D\
**Created:** [September 11, 2023, 10:37pm UTC](https://forum.itascainternational.com/t/application-of-the-dafalias-model/1169 "2023-09-11T22:37:08Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Mussie](https://yyz1.discourse-cdn.com/flex031/user_avatar/forum.itascainternational.com/mussie/32/360_2.png) [@Mussie](https://forum.itascainternational.com/u/Mussie)\
**Post date:** [September 11, 2023, 10:37pm UTC](https://forum.itascainternational.com/t/application-of-the-dafalias-model/1169/1 "2023-09-11T22:37:08Z")

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Dear all,  
I am trying to use the Dafalias Model in its version that was implemented by Zhao Cheng.

When using it in anything other than the Element-Test from the documentation, I receive the error message:

“Dafalias model: initial pressure is not positive.”

Does anyone have similar issues? Why would the Element-Test from the documentation work with negative e.g. compressive stresses while other examples like " Excavation in a Saturated Soil" (see its application on the attachment) produce the before mentioned error message.

Best regards

Mussie

[Main.dat](https://forum.itascainternational.com/uploads/short-url/9Jerr7Nid7ANyHZUzF7GJpDl58l.dat) (3.5 KB)

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**Author:** ![cheng](https://avatars.discourse-cdn.com/v4/letter/c/ecccb3/32.png) [@cheng](https://forum.itascainternational.com/u/cheng)\
**Post date:** [September 12, 2023, 3:46pm UTC](https://forum.itascainternational.com/t/application-of-the-dafalias-model/1169/2 "2023-09-12T15:46:52Z")

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Your datafile has several issues. This UDM is supposed mainly for dynamic analysis. It is a stress-dependent model, and its initial modulus is calculated by the current stress and the initial stress properties must be assigned. The doc has provided an example FISH function to do that. Here is a demonstration example:  
[oneColumn.dat](https://forum.itascainternational.com/uploads/short-url/srAwySyaOlThQyJEsw7YagJSljL.dat) (6.9 KB)  
[Kobe\_PI\_32m\_00\_acc.txt](https://forum.itascainternational.com/uploads/short-url/efk50V1kMCsZAbzHMCRk5ysxrEf.txt) (36.9 KB)

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<div class="post-metadata">

**Author:** ![Mussie](https://yyz1.discourse-cdn.com/flex031/user_avatar/forum.itascainternational.com/mussie/32/360_2.png) [@Mussie](https://forum.itascainternational.com/u/Mussie)\
**Post date:** [September 28, 2023, 7:30am UTC](https://forum.itascainternational.com/t/application-of-the-dafalias-model/1169/3 "2023-09-28T07:30:57Z")

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> [@cheng](#):
>
> our datafile has several issues. This UDM is supposed mainly for dynamic analysis. It is a stress-dependent model, and its initial modulus is calculated by the current stress and the initial stress properties must be assigned. The doc has provided an example FISH function to do that. Here is a demonstration example:

Thank you very much cheng - this is of great help for me!