Road disappears with mesh "top surface only" setting on

[Velocipede2022]

So I have merged my road (slab) into the topo mesh with intersection and then subtraction.  I would like to have the cut earth for sections and elevation not be seen so I can show, but cover with a 90%. But when I turn the "Depth" feature off on the topo mesh, the road cut disappears?  Is there a way to fix this? Maybe a different SEO technique/setting?  See attached 2 images.

Thanks!!

Operating system used: Windows 11 unfortunately 😞

[Laszlo Nagy]

Merging and SEOs work only on elements with actual 3D bodies. When you switch the Structure of the Mesh to "Top Surface Only", the Mesh ceases to be a 3D geometry, and becomes a collection of Surfaces.