How can i get the particle information in PIC?

In the PIC document, i can get the inter-particle stress by the following equation!What is the difference with the solid phase pressure? Or how is it related to the solid pressure?
In a PIC-3D hopper case, can i get the solid pressure in the different packed bed height?

The solids pressure is used in TFM, this is not the same as the PIC solids stress. PIC doesn’t use solids pressure.