I'm trying to model a small concrete lined D-shaped tunnel below the water level and I'm wondering, as the seepage module is still not fully developed, if I just need to specify the water level above the tunnel crown and ADONIS takes care of all the rest or if I need to do any additional operations.

Do I need to manually apply hydrostatic pressures on the liner elements corresponding to the water "excavation" to properly model the problem?

Thanks again.

PS: A new script will probably arise from this. I'll share it as soon as I have everything fixed.

yes you can specify water table as you mentioned or write a simple script to modify the pore pressure as you get close to the tunnel. I believe one sample script is in the forum which shows similar concept. please note that specified pore pressure will be constant throughout simulation since there is no seepage analysis.

regarding the hydrostatic pressure, the same problem exists in the commercial programs as well (at least couple that I worked with in industry). hydrostatic pressure is not considered explicitly around the liner. fundamental question is do we need to? the pp in the model will decrease the effective stress in the soil and as a result increases the earth pressure behind the structure. because of this I usually ignore the additional water pressure to avoid double-dipping. please keep in mind that constitutive model in the program is based on effective stress and increase of pore pressure results softening the soil and etc. by the way, additional pressure can always be applied outside the program separately if required which is usually done by my structure engineer colleagues.

great to hear that, looking forward to seeing your new script.

-Roozbeh

Thank you for your quick response once again, Roozbeh.

I see your point and I agree if the horizontal stresses are of the same order of magnitude of the vertical overburden. However, my problem is a tunnel in soil more or less close to the surface, where k0 should be around 0.6, so an increase of the water table reflects negatively on the pressures generated on the liner.

I should have explained better what my problem is:
We're designing a D-shaped water utility tunnel, 3m diameter, in hard clay, with the crown about 8m below the ground. Since there are a lot of curves in plan, the use of a TBM is not possible and we're going for a traditional excavation, with temporary support with closely spaced steel ribs, Bernold plates and shotcrete. For this, we're going to lower the water table to the invert level, excavate, apply the temporary support, construct the final concrete liner and only then we raise the GWT again. There's not a lot of geotechnical information available (just a couple of SPT's, same problem all the time...) so we're designing the liner very conservatively, not allowing any decompression (lambda=0) and analysing the tunnel with the liner supporting all the load.

I ran a test in ADONIS with no additional water loads and there's not a significant increase on the liner internal forces when the water level is above the tunnel, so I'll need to apply hydrostatic pressure on the elements. I'll look into that great script that's already in the forum to try to get the relevant element numbers and apply them the water pressures.

When the script is ready I'll post it. Thank you once again!

And, by the way, as usual I'm also the structural engineer here...

understood, one solution that comes to mind (which I have done several times before) is that you create one model and do your regular drained condition simulation and in the separate model apply hydrostatic pressure to the structural elements (without soil) and super impose the forces from two models get the whole picture.

Yes, I'm considering that too, using SAP2000 for the hydrostatic forces and assemble it all together (and probably use it to check for a simplified triangular soil pressure as well). I just need to be careful to check if there aren't a lot of plastified points to be able to ensure that the whole thing remains more or less elastic and that the effects may be superimposed.
Thanks again!