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what's the suitable geometry Boundary for flow analysis in plaxis ?

Khalid kamal
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, in Plaxis 2D tutorial.09; if I increased or decreased the geometry in X direction that will give me a different value to the total discharge, and if I specify geometry in flow analysis according to the radius of influence but in this example R=3000*3*(8.25e-5)0.5=81 m and that not same with the geometry in the example that may be same in case you assumed the example like a trench, so I want to know the true and what the base in geometry boundary in plaxis for flow analysis ? 

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    Dear Khalid,

    • PLAXIS 2D Tutorial 9 is a plane strain model, hence an infinitely long trench. The concept of hydraulic radius has it's basis in axisymmetry, so for radial flow towards a point, well or shaft. This is a different case.

    • The hydraulic radius is an engineering value - in principle for time is infinite, the hydraulic radius is infinite. And since a steady-state flow field is the flow fields reached after infinite time it makes sense that the influence will always be all the way up to the boundary of the model. So choosing a larger model will give you a larger influence zone.
      Therefore, when choosing the model boundaries, the hydraulic radius is something to take into account. However, the hydraulic radius is time dependent and increases in time.

    With kind regards,

    Dennis Waterman

  • 0 Offline in reply to Dennis Waterman

    Dear Dennis,

    Firstly, thank you for your reply

    Secondly, with the larger model (larger influence zone) I will get a low value for total discharge with each larger model so can I calculate maximum discharge by considering the water level outside the pit is constant and not changing?, then for predicting settlement due to lowering the water level use larger model according to the hydraulic radius? , does this make sense in the case of dewatering from the foundation pit surrounded by cut-off walls and wells inside the pit? or What should I consider as a geometry boundary in this case for accurate results in plaxis for steady state flow?

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