# Determination of strain softening parameters (SSoft Model)

**URL:** <https://forum.itascainternational.com/t/determination-of-strain-softening-parameters-ssoft-model/2212>\
**Category:** 3DEC\
**Tags:** suggestions\
**Created:** [August 20, 2025, 1:13am UTC](https://forum.itascainternational.com/t/determination-of-strain-softening-parameters-ssoft-model/2212 "2025-08-20T01:13:58Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![EdgarO31](https://avatars.discourse-cdn.com/v4/letter/e/dfb087/32.png) [@EdgarO31](https://forum.itascainternational.com/u/EdgarO31)\
**Post date:** [August 20, 2025, 1:13am UTC](https://forum.itascainternational.com/t/determination-of-strain-softening-parameters-ssoft-model/2212/1 "2025-08-20T01:13:58Z")

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Hello, everyone!

I’m new to 3DEC and also new to numerical modeling in general. I’m thinking on using strain softening Mohr-Coulomb to model concrete, but I’m struggling trying to understand how to determine the curves of softening for cohesion, and hardening of peak friction angle (degradation with plastic strain). I understand that I’m supposed to get this from lab data, but how can someone obtain the degradation of cohesion through testing (what is the methodology)? Is there any documentation I could follow related to the lab procedure? How many triaxials is enough? Are there empirical functions that could work well for concrete without running any testing? Any guidance will be appreciated!

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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:** [August 20, 2025, 1:42pm UTC](https://forum.itascainternational.com/t/determination-of-strain-softening-parameters-ssoft-model/2212/2 "2025-08-20T13:42:22Z")

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I don’t know much about lab testing, but I know that getting post-peak behavior can be very challenging. Often people assume a linear change from peak to residual properties and use a “rule of thumb to determine the plastic strain over which that transition occurs. See equation 14 [here](https://docs.itascacg.com/itasca940/common/models/imass/doc/modelimass.html?node1278#post-peak-brittleness). This document is for the IMASS model, but it is based on Hoek-Brown, so this should be applicable to Hoek-Brown as well, and probably Mohr-Coulomb too.

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**Author:** ![EdgarO31](https://avatars.discourse-cdn.com/v4/letter/e/dfb087/32.png) [@EdgarO31](https://forum.itascainternational.com/u/EdgarO31)\
**Post date:** [August 20, 2025, 11:04pm UTC](https://forum.itascainternational.com/t/determination-of-strain-softening-parameters-ssoft-model/2212/3 "2025-08-20T23:04:13Z")

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Thanks for replying! I’ll look at the document.