E' and c'/Su increase with depth (not level) in a Plaxis 3D model with varying ground surface (slope)

RE: E' and c'/Su increase with depth (not level) in a Plaxis 3D model with varying ground surface (slope)

Victor Dubasaru — Sat, 11 Dec 2021 12:57:37 GMT

Dear Dennis, many thanks for this.

Kind regards,

Victor

RE: E' and c'/Su increase with depth (not level) in a Plaxis 3D model with varying ground surface (slope)

Dennis Waterman — Sat, 11 Dec 2021 11:55:52 GMT

Dear James,

The SHANSEP concept can indeed be applied to many models - SHANSEP itself is not a model, but a way to deal with undrained shear strength. We have only implemented it for Mohr-Coulomb and NGI-ADP (User-Defined model DLL "ngiadps64.dll").

It would make little sense to apply SHANSEP to Hardening Soil or HSSmall, because those models pretty much reduce to the Mohr-Coulomb model if phi=0 is used.

With kind regards,

Dennis Waterman

RE: E' and c'/Su increase with depth (not level) in a Plaxis 3D model with varying ground surface (slope)

James Adinata — Fri, 10 Dec 2021 20:28:48 GMT

Hi Dennis, thanks for sharing. From the manual you shared, not only this SHANSHEP concept can be applied to MC, but also to other model such HS and HS Small models. However, in my PLAXIS V21, I can only apply it to MC model. Would you please help me to confirm it? Thanks!

RE: E' and c'/Su increase with depth (not level) in a Plaxis 3D model with varying ground surface (slope)

Dennis Waterman — Fri, 10 Dec 2021 09:49:22 GMT

Dear Victor,

There is no direct way to input E' and su increasing with depth, but for undrained shear strength it is possible to let PLAXIS determine the increase of shear modulus and undrained shear strength at the beginning of the calculation (so at the start of the first phase for instance) using the SHANSEP Mohr-Coulomb model. It will calculate the undrained shear strength based on the current stress state, and with a user-specified constant ratio of G/su the stiffness is calculated accordingly.

https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/46110/udsm---shansep-mc-model

With kind regards,

Dennis Waterman

RE: E' and c'/Su increase with depth (not level) in a Plaxis 3D model with varying ground surface (slope)

Victor Dubasaru — Fri, 10 Dec 2021 06:47:42 GMT

Hi Ari. I am affraid this works only when you have a flat ground / strata level. If you use this option in a model with sloping ground / strata then you will obtain overprediction of soil properties for soils in the bottom part of a slope if Zref is choosen at mid height of slope.

RE: E' and c'/Su increase with depth (not level) in a Plaxis 3D model with varying ground surface (slope)

Victor Dubasaru — Fri, 10 Dec 2021 06:45:35 GMT

James, I am using the M-C model. You are right that it can be done using the HS model, but for this you need calculate the soil stiffness with depth baed on the forumlation (formulas provided in the Plaxis manual), which is quite tedious.

RE: E' and c'/Su increase with depth (not level) in a Plaxis 3D model with varying ground surface (slope)

Ari Surya Abdi — Fri, 10 Dec 2021 03:14:08 GMT

Dear Victor,

It is possible to have E', c', and Su increase by the depth in Mohr-Coulomb soil model. You can go to advanced option in soil parameters input. In Hardening Soil, you can also use the strength increase by the depth using this way.

RE: E' and c'/Su increase with depth (not level) in a Plaxis 3D model with varying ground surface (slope)

James Adinata — Thu, 09 Dec 2021 21:35:18 GMT

I agree with you, I am having the same issue but with PLAXIS 2D.

What soil model are you using? The Hardening Soil allows the variation of stiffness based on stress level.

However, I am still stuck on how to vary the strength accordingly.