# Liner coupling stiffnesses

**URL:** <https://forum.itascainternational.com/t/liner-coupling-stiffnesses/1755>\
**Category:** FLAC3D\
**Created:** [October 14, 2024, 3:16pm UTC](https://forum.itascainternational.com/t/liner-coupling-stiffnesses/1755 "2024-10-14T15:16:11Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Adams](https://avatars.discourse-cdn.com/v4/letter/a/96bed5/32.png) [@Adams](https://forum.itascainternational.com/u/Adams)\
**Post date:** [October 14, 2024, 3:16pm UTC](https://forum.itascainternational.com/t/liner-coupling-stiffnesses/1755/1 "2024-10-14T15:16:11Z")

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I read the manual on estimating the normal and shear stiffnesses for liners. From the formula stated in Equation 1 (Liner Structural Element 3D), how to calculate/measure the smallest dimension in the adjoining zone is not clear. I even tried to back-calculate the smallest dimension (estimated as 0.0633) of the model in the manual (embedded retaining wall) see attached but I still could not figure out where they measured the value. Please I would appreciate how I could estimate the smallest dimension of an adjoining zone in the normal direction.

![Calculation](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/2X/8/8a8bd186a180c7976abea26311f2ac4c85af7435.png)

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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:** [October 14, 2024, 8:54pm UTC](https://forum.itascainternational.com/t/liner-coupling-stiffnesses/1755/2 "2024-10-14T20:54:26Z")

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In this model, `delta_Z_min` is 1.0 from the command `zone create brick size 11,1,11`.

For other cases,

- You can manually measure the distance between two points in a likely zone in the grid plot by clicking the measurement button.
- You can query a likely zone to obtain its volume, then estimate its size by taking the cube root of this volume.
- You can also write a FISH function to loop through all zones adjacent to the liner to estimate the minimum size.

Also, remember there is a factor of 10 in the recommendation. In this example, the optimal Kn (Ks) would be around 10×6.33e9/1.0 = 6.33e10, and a slightly higher value 1e11 is used.

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**Author:** ![Adams](https://avatars.discourse-cdn.com/v4/letter/a/96bed5/32.png) [@Adams](https://forum.itascainternational.com/u/Adams)\
**Post date:** [October 15, 2024, 1:46am UTC](https://forum.itascainternational.com/t/liner-coupling-stiffnesses/1755/3 "2024-10-15T01:46:24Z")

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Thank you for your explanation. I understand now.