Overturning of Footing - Base Pressures

Question

Hi 
 I have been looking at a model in Plaxis3D for a shallow footing overturning under an applied shear and moment. 
 When i look at the results for the interface element at the base for normal pressure, it shows the front of the footing in compression (negative pressure) and the back of the footing in tension (positive pressure). This would intuitively seem correct except that the footing contact should not be able to take any tension loads if the footing starts to lift, yet the positive pressure suggest tension between the back of the footing and soil foundation has developed. 
 Am i interpreting the results correctly? or is there an issue with how i have modelled this problem in Plaxis 3D? 
 Example outputs below 
 Thanks

Micha van der Sloot · Answer

Hi Timothy 
 
 Two things might explain this: 
 
 is the soil model you are using in the interface having a tensile strength defined? For instance if tension cut-off is activated at a tensile strength of zero, then in the plastic points plot, you should also see tension cut off points in this area. 
 from the plots, it seems you have your interfaces tightly wrapped around the concrete footing. Care should be taken here by slightly extending the interfaces (with Rinter = 1.0/rigid for the extension), as mentioned in the PLAXIS 3D Reference manual in the part about " Interfaces around corner points ".

If that does not solve your issue, can you please submit a service request here: apps.bentley.com/.../ProductSupport&#160;