Somehow I don't think they had this in mind...
If I understand correctly, it's more like to have a space
surrounded by earth from
every side (including the top), like for example, an underground car parking area under a city square park...
Well, if you do not have to show it in a
3-D section, you can use your toposurface with a
poche set up to the level of the top of your underground building (so it sits on top of your building and shows correctly in a
normal 3-D view) and for a
standard 2-D section you can fill your earth pattern around, using Filled Region...
see picture 1
However, if you need a
3-D section you do exactly the same, but instead of using a Filled Region (in 3-D it wouldn't work), create an in-place family, of category "
Topography", which could be just several joined extrusions with the material set to show earth pattern in cut section... You could "wrap around" your underground structure using as many these "
Topography" objects, as needed... But because for some strange reason, in 3-D view the Toposurface poche depth setup doesn't have any effect (
), I simply (or sometimes not so simply...) model an approximation of a toposurface (again as an in-place family), using a combination of extrusions and voids. It doesn't need to be that accurate - after all, for the accurate shape of toposurface they can always refer to Site Plan and Site Sections...
see picture 2 and 4
Of course, if you need both 2-D and 3-D sections, don't bother creating a 2-D section using the first method, just use the second method and show the effects in both views...
see picture 3 and 4.