Introduction

Automating your geotechnical analyses with PLAXIS can significantly speed up your workflow, especially for parametric studies or complex projects. 
This article shows how to use a Python script and the subprocess module to launch and control PLAXIS without opening the application manually.

The main scope of this article is to explain how to use Python's subprocess module to start the PLAXIS application as a separate process in Windows OS. 
Once PLAXIS is running, you can connect to Input or Output using the plxscripting library to send commands, build models, run calculations, and extract results.

The Python script is divided into several parts, from launching the application to closing it down cleanly.

 

Python script - Example

The full Python script is provided as a compressed file (ZIP) at the end of this article. Below each part is explained in detail, so you can adjust it according to your preferences.

Import modules

As always at the beginning of a Python script it is advisable to add any general import operations. In the article we need to import the subprocess module (official Python documentation).

Part 0: Setting Constants

Before we start, it is important to define some key constants.

Variable	Description
plx_input_path	The full path to the Plaxis2DXInput.exe or Plaxis3DInput.exe on your machine. Make sure this is correct for your installation.
plx_input_port	The port number for the API server. This can typically be any free port; 10000 is the default value.
plx_password	The password for the server. You must replace 'YOUR_PASSWORD' with the secure password in PLAXIS. This password can be the same as the one in the ‘Configure remote scripting server’ window under Expert menu, from Input or Output.

Part 1: Launch PLAXIS Input

This is where we use the subprocess.Popen function to start the PLAXIS Input application. Here, we pass the aforementioned variables as arguments. Notice the command arguments required:

• --AppServerPort: Specifies the port that PLAXIS will listen on for API commands.
• --AppServerPassword: Sets the password required to connect to the API.

Part 2: Connect to the PLAXIS API 

Once PLAXIS is running, we need to establish a connection to the scripting server. This is done with the new_server function from the plxscripting.easy module.

• s_i (server for Input) and g_i (global object for Input) are the two variables you will use to send commands to the PLAXIS Input application.

Part 3: Main Python script for your PLAXIS Input automation

This is the core of your automation script. Here, you can script all the actions you would normally perform manually in the PLAXIS UI.

• s_i.new() creates a new project.
  Alternatively, you can use s_i.open() to open an existing .p2dx or .p3d file.

• After creating or opening a project, you can add your code to define materials, geometry, structures, mesh, configure the construction stages, and then calculate the project.

Part 4: Launch and Connect to PLAXIS Output

To analyse the results, you need to launch and connect to the PLAXIS Output program.

• g_i.view(g_i.Phases[-1]) opens the PLAXIS Output and loads the results for the last calculated phase. It also returns a new port number for the Output server, which we can store in a variable (output_port) to reuse in the next step.
• You then use new_server function again, but this time with the new output_port, to get the s_o (server for Output) and g_o (global object for Output) variables. By default, PLAXIS will pick the first available port following 10000. If no other PLAXIS instance is open apart from the PLAXIS Input, the Output port will be 10001.

Part 5: Main Python script for your PLAXIS Output automation

With the connection to the Output program established, you can now add commands to extract results, create plots, or generate cross sections.

Part 6 & 7: Closing the PLAXIS Sessions

It is crucial to close the server sessions properly to release the PLAXIS license.

• s_o.close() and s_i.close() will close the connection to the Output and Input servers, respectively. This allows you to potentially open another project in the same PLAXIS instance.

Part 8: Terminate the PLAXIS Application

Finally, plx.terminate() sends a command to the operating system to close the PLAXIS application that was started by subprocess.Popen function in the beginning. This ensures a clean shutdown of the entire process.