Stiffness matrix is nearly singular and cannot be solved error 20

The error "Stiffness matrix is nearly singular and cannot be solved" with error code 20 in PLAXIS 3D typically indicates that the stiffness matrix is close to being singular, which means it is nearly non-invertible. This can occur due to several reasons, including:



1. Incorrect Boundary Conditions (BCs): One common cause is the incorrect specification of boundary conditions. This can include surface-to-surface contact that is not correctly defined.


2. Over-Activated Form-Finding: In RF-FORM-FINDING calculations, activating form-finding for too many elements can lead to this error. It is essential to check which elements have form-finding activated and deactivate unnecessary ones.


3. Modeling Issues: The error can also be caused by modeling issues, such as incorrect geometry or meshing.





To resolve this error, you should:


1. Check Boundary Conditions: Verify that all boundary conditions are correctly specified, ensuring that surface-to-surface contact is properly defined.


2. Optimize Form-Finding: Review the elements with form-finding activated and deactivate any unnecessary ones.


3. Review Modeling: Inspect the model for any geometric or meshing errors that might be contributing to the issue.


Additionally, you can refer to the PLAXIS 3D tutorials for beginners to ensure proper modeling and setup.

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