Strain inside a geogrid

Hello,

I am doing a simulation for a geogrid-reinforced piled embankment using Plaxis3D. I encountered a problem when trying to get the tensile strain in the geogrid, but it seems that it cannot be done directly. How can we obtain the strain from the geogrid element?

ps : I created a surface and then assigned it as a geogrid.

Thank you.

Cristina