Internal "Islands" Surfaces

I’ve recieved a series of LeapFrog (GeoTechnical) models in DXF format - they’re big files so I’ve imported into GlobalMapper v26 and then exported as LandXMLs,

These Models have “islands” inside and I’m trying to combine them by “Combine Surfaces” it just won’t recognise internal boundarys when combining (but does when individual surfaces)

Any suggestions please?

just thinking real quick. export as a 3d DXF and reimport. generate surface from the 3d faces.

another way would be to drop a site improvement. The SI doesnt need to have a material. just select none and name it usually how its been named is NULL.

Thankyou Francisco - turns out I also had a corrupted XML / DXF Surface for one of the surfaces which was (hopefully) the issue - being recreated by GeoTech now