Openroads designer: Combine two or more terrain models to get the lowest elevations of the combined two surfaces

Hi,

I wish to merge two or more surfaces / terrain models(excavation models), so i end up with the complete bottom part of the excavation. Is there any way to do this?
I am using ORD 2021 R1. I am also able to use InRoads SS2 if there is a way to do it in InRoads :)

Best regards,
Klaus