Hi
In rock, it is common to have a linearly varying in-situ stress (described by a slope + and INTERCEPT). Software like RS2 supports this kind of in-situ stress definition. Will PLAXIS support it as well? It would be really helpful.
Thanks
Omar,
I'm assuming that you're referring to the initial horizontal stresses in which case you can use the Ko parameter on the Initial tab for the slope of the in-situ horizontal stress. To get an intercept the ground surface, you would need to start the analysis with an pre-overburden pressure (POP).
If using the MC model there is no POP parameter on the Initial tab, in which case you can include a strata of 1 m. with a unit weight of the POP in the model and remove it in a null step to obtain the initial stresses.
In either case, I recommend checking the insitu stresses in the output to insure they are as expected.
Martin
Answer Verified By: Omar Baltaji
Thanks Martin
The POP is used to vary the vertical stress. However, I need to change the horizontal stress WITHOUT changing the vertical stress. The only option to change the horizontal stress which i can find is the K0, but this doesn't have an intercept.
Thank you
Dear Omar,
The POP does not change the vertical stress, it changes the horizontal stress as Martin already mentioned.The vertical stress will remain the same based on soil wait, but by introducing a POP the stress state will be based on primary loading + elastic unloading which causes an increased K0, but be aware that that increase reduces with depth.
With kind regards,
Dennis Waterman
Thanks Martin and Dennis
Yes the POP will solve the issue, because different POP can be applied at the top and bottom of a layer. I just verified that. I didn't realize that was the case and that confused me. And yes POP changes the horizontal stress not the vertical. Thanks Dennis for correcting me on this.
I just tried this solution in Plaxis 2D (2018) and it worked well. I am using Mohr Coulomb and Hoek Brown models. However, the same functionality seems to not be available in Plaxis 3D (2020). It is available for hardening soil but I was only able to use a fixed POP (I couldn't set different POP for top and bottom of a layer).