Hi All,
I am trying to model the impact of flood water on a sheet pile flood defense situated at the top of a clay river bank.
How do I model the maximum flood level without changing the overall groundwater regime that I have defined in the 'Flow Conditions' tab? Performing undrained analysis for duration of flood event given embankment is clay and flood level will be short lived. In short, just looking to have the flood water act as a surcharge load without creating porewater pressures in the soil below it. The soil porewater pressures and excess generated during the flood level should reflect the existing groundwater regime which is set just above the toe of the existing river bank.
Any help is much appreciated.
Dear Iain,
From the description, I am a bit confused as to what exactly this represents in reality. When water floods this means that the water level will rise. This should have an effect on the pore water pressures of the soil right under it.
You mention you want to have a surcharge load due to the flood water, which is what the purpose of the external water loads is when a physical water level is above the surface. So, this is applied already only with the presence of the phreatic level.
Now, the question of how fast the flooding will affect the pore water pressures of a low-permeable soil, e.g. clay, is something that the calculation should answer. This can be done by running a time-dependent fully coupled flow deformation analysis. In such analysis, the permeabilities are one of the most important input and directly affect the results (other being the boundary conditions defined).
An example is our tutorial lesson of the rapid drawdown, in which you can see the effect of time in the distribution of pore pressures: PLAXIS 2D Tutorial 09: Stability of dam under rapid drawdown - PLAXIS | SOILVISION Wiki - PLAXIS | SOILVISION - Bentley Communities
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Hi Stefanos, thanks for the reply.
Apologies - I think my question was a bit disjointed but I think I have solved what I was trying to do.
Essentially, I have a steady state groundwater level associated with the problem and all I was wanting to do was to keep that steady state groundwater level the same while 2 levels of flooding occurred.
I have set the soil clusters to a custom water level so that they are calculating the steady state pore water pressures based on this steady state level, but then set the flood level as the global water level so that any excess pore water pressures that develop are because of this global water loading. Hope that makes more sense now!
My company doesn't appear to have a licence for the flow module within Plaxis 2D so i don't think i'm able to perform a coupled flow deformation unfortunately.
Many thanks,
Iain
That can work, indeed. Note that the main difference when handling a custom water level and a global water level is that the latter is considered physical water being present, thus external water loads are generated.
You are right that without the PlaxFlow module it is not possible to run a fully coupled flow-deformation analysis, but you can use the steady state ground water flow that is offered.