# Structural elements and fluid interaction

**URL:** <https://forum.itascainternational.com/t/structural-elements-and-fluid-interaction/846>\
**Category:** FLAC3D\
**Created:** [November 30, 2022, 4:27pm UTC](https://forum.itascainternational.com/t/structural-elements-and-fluid-interaction/846 "2022-11-30T16:27:20Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Francesco\_IT](https://avatars.discourse-cdn.com/v4/letter/f/b5a626/32.png) [@Francesco\_IT](https://forum.itascainternational.com/u/Francesco_IT)\
**Post date:** [November 30, 2022, 4:27pm UTC](https://forum.itascainternational.com/t/structural-elements-and-fluid-interaction/846/1 "2022-11-30T16:27:20Z")

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Dear All,  
I need to model embedded diaphragms as impervious elements at the base of a dam and, for the sake of simplicity, I would like to use structural elements rather than zone elements. Could you clarify me which are **embedded waterproof elements** (liner?) and which are not (shall?)?  
Thank you!

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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:** [November 30, 2022, 4:49pm UTC](https://forum.itascainternational.com/t/structural-elements-and-fluid-interaction/846/2 "2022-11-30T16:49:39Z")

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If we use a liner, it will sperate zones. At the separation, it will be considered zone boundaries (both sides) - by default, it assumes impervious fluid boundary condition, the same as those normal side boundaries.

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**Author:** ![Francesco\_IT](https://avatars.discourse-cdn.com/v4/letter/f/b5a626/32.png) [@Francesco\_IT](https://forum.itascainternational.com/u/Francesco_IT)\
**Post date:** [December 1, 2022, 9:03am UTC](https://forum.itascainternational.com/t/structural-elements-and-fluid-interaction/846/3 "2022-12-01T09:03:35Z")

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Dear Cheng,  
thank you for your quick reply. If I well understood, the embedded liner can only be placed at zone faces and it’s not possible to place it as floating element, crossing grid zones. Or is it possible to use floating liner element crossing zones keeping the impervious fluid boundary?

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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:** [December 1, 2022, 6:21pm UTC](https://forum.itascainternational.com/t/structural-elements-and-fluid-interaction/846/4 "2022-12-01T18:21:14Z")

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Liner has to be placed at zone faces for the interaction with zones via deformable normal and shear links.  
Shell and Geogrid elements can be “floating” but I am not sure if shell and geogrid are applicable to your model.