# Problem with calibrating modulus degradation curve

**URL:** <https://forum.itascainternational.com/t/problem-with-calibrating-modulus-degradation-curve/1907>\
**Category:** FLAC\
**Created:** [January 22, 2025, 10:34am UTC](https://forum.itascainternational.com/t/problem-with-calibrating-modulus-degradation-curve/1907 "2025-01-22T10:34:23Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![horacelo](https://avatars.discourse-cdn.com/v4/letter/h/df705f/32.png) [@horacelo](https://forum.itascainternational.com/u/horacelo)\
**Post date:** [January 22, 2025, 10:34am UTC](https://forum.itascainternational.com/t/problem-with-calibrating-modulus-degradation-curve/1907/1 "2025-01-22T10:34:23Z")

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![degradation curves](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/2X/2/2bf7a8ef2b3a87cb37c30ab65aee5887f80656a3.png)  
Hello everyone, I am currently calibrating the modulus degradation curve to a published curve, using the sigmoidal-3 model. Using the provided one-zone code in FLAC3D (One-Zone Sample Exercised at Several Cyclic Strain Levels), I get the parameters a=1.032; b=-0.517; x0=-1.758, which are similar to the curve of Seed and Idriss. However, when I plot the curve in Excel using the formula of sigmoidal-3 curve, it does not match at all. I wonder if anyone has also encountered this inconsistency?

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**Author:** ![jwang](https://avatars.discourse-cdn.com/v4/letter/j/b782af/32.png) [@jwang](https://forum.itascainternational.com/u/jwang)\
**Post date:** [January 22, 2025, 4:15pm UTC](https://forum.itascainternational.com/t/problem-with-calibrating-modulus-degradation-curve/1907/2 "2025-01-22T16:15:05Z")

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Using those parameters, the Sig3 model shows consistent results, see the plot from Excel, you may check your inputs.

 ![image](https://canada1.discourse-cdn.com/flex031/uploads/itasca/original/2X/f/f20e77122bcbd37335ef551daa2f40366958bc65.png)

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**Author:** ![horacelo](https://avatars.discourse-cdn.com/v4/letter/h/df705f/32.png) [@horacelo](https://forum.itascainternational.com/u/horacelo)\
**Post date:** [January 23, 2025, 8:19am UTC](https://forum.itascainternational.com/t/problem-with-calibrating-modulus-degradation-curve/1907/3 "2025-01-23T08:19:11Z")

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Thank you very much for the verification.  
It seems in the sigmoidal-3 curve, shear strain in L=log10(shear strain) is not in the original unit, but is in percentage.