Plaxis 3D FEM point cloud data modelling and the safety factor

Question

Dear 
 I modeled a real point cloud data in to the Plaxis 3D FEM and the data comes from the real survey of an investigation. In this regard, it is obvious that we have a complex surface from the real data. In this analyze, we want to investigate the land sliding hazard in different areas and controlling the safety factor in different areas. The phases are determined as the following: 
 Initial phase: 
 Calculation type: Gravity loading 
 Loading type: staged construction 
 &hellip; 
 
 2nd phase: 
 Calculation type: Safety 
 Loading type: Incremental multipliers 
 Msf: 0.1 
 &hellip; 
 Question 1: Does the Plaxis 3D FEM has this ability to define some specific area or draw some lines to determine the safety factors in these areas and lines and show the worst lines and points with fewer safety factor on the model? I want to evaluate which area and lines have the lowest safety factor on them. 
 Question 2: If I go to the &ldquo;view calculation results&rdquo; and draw a curve with the x-axis defined with the &ldquo;step&rdquo; instead of defining the specified nodes and in the y-axis defining the multiplier &ldquo;Sigma Msf&rdquo;, the Plaxis shows me for each step, the worst node has the maximum reduction in the shearing parameters and finally shows me the failure in a specified node with the maximum reduction in the shearing failure which reveal the safety factor. In this regard, if I want to know the other nodes that reached the failure then after that, what should I do? How could I understand the other failed nodes in the model in the following because I want to know the failed points and values of the safety factor in different area of the model to define specific design for them? 
 I would be thankful if you may please guide me in this process 
 Thanks for your response 
 I look forward to hearing from you 
 Sincerely

Stefanos Papavasileiou · Answer

Dear Amir, 
 I will answer both of your questions below: 
 1. PLAXIS computes a global safety factor. That means that the calculation will find the most critical failure mechanism in the model you have and determine a safety factor based on that. Therefore, the value you get would be the lowest safety factor based on what PLAXIS has determined to be the most critical failure zone. 
 Note that sometimes PLAXIS calculation focuses on a local failure that from an engineering point of view is not relevant or is to be disregarded. PLAXIS offers an option to exclude part of the model using the Apply strength reduction option for volumes. Therefore, you can partition your geometry in the area of the irrelevant local failure and uncheck the option: 
 For more information, please check our Reference manual. 
 2. The curve plot you create (as you mention) is "step vs. &Sigma;Msf". That again refers to the most critical failure mechanism found by the calculation. If you want data from other areas of the model, you can select as many curve points as you want and plot the relevant data. 
 I would advise you to follow our webinar on Using PLAXIS to Determine Factors of Safety: event.on24.com/.../6BA8A61A920F589C3E5C23DA3B23FDD6

Stefanos Papavasileiou · Answer

Dear Amir, 
 I noticed you created a Service Request which is the quickest way to get Support. We will come back to you as soon as possible. 
 Note that the Forum is open to all geotechnical engineers, not just the PLAXIS Support team. Hopefully, more fellow geotechnical engineers can comment on any topic. 
 
 Just to give you a quick comment, I am not sure if I understand what you are actually asking for. PLAXIS provides the most critical failure mechanism during calculation. Then, based on that you can inspect the results to be able to identify the area and location of this critical failure zone. 
 Are you referring to options that Limit Equilibrium Methods provide?

Stefanos Papavasileiou · Answer

Some additional and helpful webinars: 
 Using PLAXIS to Determine Factors of Safety https://event.on24.com/wcc/r/2165515/6BA8A61A920F589C3E5C23DA3B23FDD6?partnerref=GeoAnalysisBC 
 Combining a PLAXIS analysis with SLOPE/W's Limit Equilibrium for slope stability https://event.on24.com/wcc/r/3876745/747A28EEA489A7B7487D4E0B379BB4B7?partnerref=GeoAnalysisBC