Optimize excavation calculation time for wall horizontal displacement criteria

Earth Retaining Stabilizing Structures (ERSS) of excavations in design need to satisfy both ultimate and serviceability limit states. One of the common serviceability limit state criteria is the retaining wall’s horizontal displacement. The wall horizontal displacements should be smaller than a horizontal displacement limitation (criterion). If the wall displacements are larger than the limitation, the excavation model should be redesigned and recalculated.

Some complex excavation projects can have a lot of phases modelled in PLAXIS and each phase calculation might take a long time to finish due to model complexities and used advanced material models. It would save time if the calculation stops at an intermediate phase when the calculated horizontal displacement is larger than the limitation. Otherwise, it takes much more time than necessary if the program continues to calculate and finishes at the last phase or if a calculation error is encountered, for example, a soil body collapse error.

For an example of such an excavation problem, we will use a project that has 10 phases, and the wall horizontal displacement limitation of 5.0 cm is set as a criterion. If the maximum horizontal displacement of a wall at Phase_6 is 6.0 cm, the calculation should stop at Phase_6 so that the geotechnical designer will adjust the model to meet the design criteria. The calculation does not need to run until Phase_10, the last phase.

To overcome this issue with calculation time, this Python script is developed to stop the calculation at an intermediate phase if the horizontal displacement is larger than a given limitation in excavation problems. Functions and overall workflow in the script are shown in the figure below and explained in detail in the script text. Note that the unit of the wall horizontal displacement limitation is the same as the unit of length of the project.

Figure. Functions in the Python script

A video to demonstrate how to use this script is shown below.

Conditions

The following should be considered about the code above:

• The script requires the existence of retaining wall plate(s)
• The model should be ready for the calculation: meshing and selected points have been done before you run this script.
• The code will run until the horizontal displacement of a selected wall exceeds the criterion or the last phase or any calculation error is encountered.
• To see all prerequisites, please refer to this article Using PLAXIS Remote scripting with the Python wrapper

Usage instructions for Python script

To use this Python script:

1. Download the file (use Save As...)
2. Copy this script into this folder: <PLAXIS 2D installation folder>\pytools\input
   By default for PLAXIS 2D CONNECT Edition V22, this is at:
   C:\Program Files\Bentley\Geotechnical\PLAXIS 2D CONNECT Edition V22\pytools\input
3. Launch PLAXIS Input with a project with plates
4. Make sure you are in Staged construction mode and ready to start the calculation (the mesh has been generated, points for curves are selected)
5. In the Expert menu, go to Python > Run Python tool. Here you should see the name of the Python file. When selecting it, it will start with the execution of the script.

You can also choose to use the Expert menu > Python > Run script > Open... to manually open and run the script.

Alternatively, you can open SciTE via the PLAXIS 2D menu > Expert > Python > Editor and load the Python script to run it.

Version

The script is tested with PLAXIS 2D CONNECT Edition V22 and Python 3.8 using PLAXIS 2D Tutorial 06: Dry excavation using a tie back wall from the PLAXIS Tutorial Manual.

Disclaimer

Copyright (c) Plaxis bv. All rights reserved. Unless explicitly acquired and licensed from Licensor under another license, the contents of this file are subject to the Plaxis Public License ("PPL") Version 1.0, or subsequent versions as allowed by the PPL, and You may not copy or use this file in either source code or executable form, except in compliance with the terms and conditions of the PPL.

All software distributed under the PPL is provided strictly on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESS OR IMPLIED, AND LICENSOR HEREBY DISCLAIMS ALL SUCH WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT, OR NON-INFRINGEMENT. See the PPL for specific language governing rights and limitations under the PPL.

Downloads

• Stop calculation at wall horizontal displacement limit [zipped package]

See also