# Joint Plane FOS

**URL:** <https://forum.itascainternational.com/t/joint-plane-fos/743>\
**Category:** 3DEC\
**Tags:** tips\
**Created:** [September 7, 2022, 2:17pm UTC](https://forum.itascainternational.com/t/joint-plane-fos/743 "2022-09-07T14:17:11Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Damir](https://avatars.discourse-cdn.com/v4/letter/d/7993a0/32.png) [@Damir](https://forum.itascainternational.com/u/Damir)\
**Post date:** [September 7, 2022, 2:17pm UTC](https://forum.itascainternational.com/t/joint-plane-fos/743/1 "2022-09-07T14:17:11Z")

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Dear users,

will somebody help me. What _Joint Plane FOS_ command (screenshot is attached) calculates by default?

Thanks in advance!

Damir

 ![FOS_command](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/1X/9f9be48246968c9c481111b6e1db5c1730372dda.jpeg)

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**Author:** ![jhazzard](https://avatars.discourse-cdn.com/v4/letter/j/4af34b/32.png) [@jhazzard](https://forum.itascainternational.com/u/jhazzard)\
**Post date:** [September 9, 2022, 6:44pm UTC](https://forum.itascainternational.com/t/joint-plane-fos/743/2 "2022-09-09T18:44:08Z")

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This is just the shear strength divided by the shear stress. So if (cohesion + tan(friction)\*(normal force)) = 10 MPa and the shear stress is 5 MPa, the plot will show a value of 2. If the joint is sliding, the stress equals the strength, so it will show a value of 1.

If it’s failing in tension, it shows 0.

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**Author:** ![Damir](https://avatars.discourse-cdn.com/v4/letter/d/7993a0/32.png) [@Damir](https://forum.itascainternational.com/u/Damir)\
**Post date:** [September 10, 2022, 5:10pm UTC](https://forum.itascainternational.com/t/joint-plane-fos/743/3 "2022-09-10T17:10:59Z")

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Thanks Jim!

Really appreciate the answer. Does it mean that in the case of _cyclic_ loading cohesion and tension are unrecoverable? In other words, if joint is sliding or opening for the first time, cohesion and tension drops to zero and remain zero till the end of the calculation? By the way, is the _Join Plane FOS_ reachable by Fish command?

Thanks!

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**Author:** ![jhazzard](https://avatars.discourse-cdn.com/v4/letter/j/4af34b/32.png) [@jhazzard](https://forum.itascainternational.com/u/jhazzard)\
**Post date:** [September 16, 2022, 5:48pm UTC](https://forum.itascainternational.com/t/joint-plane-fos/743/4 "2022-09-16T17:48:43Z")

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Well, the joint plane FOS plot item doesn’t change anything. It is only used for plotting. You can get the FOS with FISH function block.subcontact.sratio.

For your second question, yes, by default the cohesion or tension will drop to 0 when the strength is exceeded. You can specify a residual cohesion or tension that is not 0 if you want. With the mohr model, the cohesion will never recover back to the initial value.

You can use the softening-healing mohr model ([here](http://docs.itascacg.com/3dec700/3dec/docproject/source/theory/softhealmc/softhealmc.html?node2183)) if you want the cohesion to recover when the joint stops sliding.