Unwanted water load appear in sectional face when the ground surface formed by importing

Hi, I am a newbie in Plaxis 3D. I am setting the model of deep excavation with lateral support.  

First, I creat the soil/existing ground by borehole only, and i set some volume to deactivate since the ground surface is not flat. And I creat all excavation volume by "structure: surface with extrude tool", it is not accurate due to the excavated surface with the different gradient in real case. The result generated is reasonably close.

Then, I found that the existing ground surface can be imported in borehole setting. I imported the surface in DXF format and it looks really great!! After that (re-calculation), it fails just in stage 1 (inserting sheet pile wall without any excavation). I dont know whats going on and i found that there are some external water load adding to the sectional face, which does not appear in my first method.

Please help.... Thank you.

Best Regards,

William

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  • Dear William,

    The problem you experienced can happen due to a small inaccuracy of the created geometry (usually from import).

    Most of the times this inaccuracy is too small to be noticed while checking the model, however, the program will indicate this when applying the default fixities.

    By default all lateral (and bottom) boundaries have fixities. The default fixities are applied to the extremes of the model, i.e. Xmin, Ymin, Xmax, Ymax, Zmin, which means that if one of the lateral boundaries, as correctly mentioned by Rushan, is not perfectly vertical, then some part of the geometry will not have any fixities as the whole lateral boundary is not the extreme of that model, but probably some part of the geometry.

    As a result, when fixities are not applied and a water level is present, external water loads are applied to the model, which are not supposed to be generated at all.

    In that case, you need to inspect the part of the geometry that is missing the fixities and show external water loads and go back to Input and try to fix it.

    One way is to check the importance file and fix the issue before importing it to PLAXIS.

    Another way is to force an intersection between a vertical surface you can quickly create in Input and the soil volumes. The intersect command can be executed in the command line as follows:

    intersect BoreholeVolume_1 Polygon_2  # for two objects

    intersect BoreholeVolume_1  BoreholeVolume_2 BoreholeVolume_3 Polygon_1  # for multiple objects

    As a result, the manual intersection will create new objects which will be editable in Structures mode. Then, you can delete the parts that seem to "stick out" to fix the geometry. Typically you can check the command response to identify all created objects from intersections.

    If you encounter any similar issues you cannot fix, please submit a service request.

    Then, one of our support engineers can help you in detail: https://apps.bentley.com/srmanager/ProductSupport

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