Hi,
I am trying to model a hypothetical case of stability of an embankment subject to river water level fluctuations. As can be seen in the picture attached, I had assigned an external water level (AB) approximately 2 m above the toe of the embankment. However, PLAXIS automatically considers the water level to be continuous to the far end in the right (BC), but this is not what I am looking at. Could you please suggest why PLAXIS considers the water level to be continuous (up to point C)? Is there a way to create a model with water level (AB) only?
Thank you in advance.
Best Regards,
Sam
Sam,
Setting up the water conditions in Finite Element Analysis is tricky. Plaxis likes to have the conditions set all the way from the left to the right boundary. If you draw it part way (like from A to B) you get the result that you show. What you need to do is draft the phreatic level all the way from A to C, even if this involves dropping it down to the bottom of the model (which would be unrealistic). When you set up the phases for the water level fluctuations, draw the entire phreatic surface again but only change the water level from A to B. Keeping the part from B to C unchanged.
Check the pore pressure at each phase to be sure Plaxis is doing what you think it should be doing.
good luck,
Martin
Hi Sam,
I presume you're trying to model only the external load caused by the river assuming that the soil remains dry, because I can't think of another reason to only model the part AB? If that is so, you may just want to model the external water load as a normal distributed load and vary that rather than using a water level.
With kind regards,
Dennis Waterman
Dear Sam,
I agree with Martin, that in the finite element world there is no guessing. It is not possible for the program to not have any configuration when it comes to the model boundaries, e.g. fixities, groundwater, etc..
That is why when drawing part of a water level, we automatically assume it goes all the way to the end. If no water level is considered PLAXIS would still, automatically configure open, seepage boundaries (bottom is by default set to closed) unless you choose otherwise. See Model explorer > Model conditions > GrounwaterFlow.
Of course, as Dennis mentions, if the purpose is to only include the external load in the analysis, you can replace that with a line load related to the physical water load you have.
Dear Martin, Dennis and Stefanos,
Many thanks for your response. I am going to try modelling external water level as a normally distributed load. This seems to be the only possible way. Thank you once again for your response. Really appreciate it.
Regards,