Is the solid in the DWG an actual solid, or is it a Civil 3d object of some sort? If you select i tin Civil 3d what does the object type say in the properties pallet? If not ‘solid’, you’ll want to break it down into native dwg native content. You may want to verify the file in base AutoCAD (without Civil 3D) as you go just to be sure.
From there, if memory serves, the SAT export will always be a lower quality than the native DWG as it will tesselate the shape. For most uses this is fine, but as you an see the tessellation isn’t always idea. Breaking things into smaller pieces can help a lot. Note that you also have second round of quality loss when you bring the sat into the .rvt file… less formats and go-betweens is better.
In the end the ‘best’ way forward for this type of work will depend on your end goal. if just displaying the geometry, why not just import the DWG into a family and create an instance (least amount of data loss). If you need to host stuff, you likely want to extract the source content from Civil (ie: the alignment, profiles) and build native Revit content from those if you need solids. If you only need surface geometry, why not built a surface form the shape and use that?
I need a native revit element because I need to cut with other elements and get the final volume.
But it seems this is a bit of a workflow fail because as i have just been told the solid was retrieved from a revit element to use it in civil to cut with topography. And now we wanted to get that back into revit.
Now as I know that I´ll just try to do everything in revit. So I will try to get surface with civilconnect and see if I can get it´s geometry for modifying my solid.