Negative Load Advancement

Dear Omar,

A negative ΣΜstage indicates that the calculation tried to apply the loads for that specific phase (or deactivate them, depending on what is happening) and it could not find equilibrium. Therefore it took some negative steps to correct that but apparently, it failed. 

So, consider that you want to apply a load =100 kPa in one phase. The calculation will take some steps to fully apply the 100kPa. Each step a small position of the load is applied, e.g. 10kPa but when this cannot be solved (as out-of-balance introduced) then the calculation tries to take a small unloading step to help it reach equilibrium. So from 10kPa, it will reduce it to 8kPa or lower until all Max unloading steps (by default set to 5) are performed.
For the overall multiplier, ΣMstage, that is a negative step.

A nice read can be found here: https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/45973/load-activation-in-time

Our appendix in our Reference manual mentions that this issue is typically related to numerical reasons. The first step is to inspect Output plots that can assist in determining the cause:

• deformed mesh
• total displacements (shaded plot)
• incremental displacement (shaded plot and/or arrows)
• total deviatoric strain (shaded plot)
• incremental deviatoric strains (shaded plot)
• plastic points
• when applicable: excess pore pressures (pexcess)

A combination of these plots will usually give insight into what is happening.

The issue might be related to the generated mesh so re-meshing in the area where any of the aforementioned plots point to may be needed.

You can consider adjusting the Max unloading steps to a higher number (start with 10) to see if the failure is local and can be overcome.

In some cases adjusting the Arc-length control also helps: https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/45924/iterative-settings-influence-of-arc-length-control

Thanks for your response, Stefanos. I figured out the reason for the error.

Awesome!