I don't have a solution to your question, but I did recently create a Mesh in ARCHICAD (21) from a Civil3D TIN.
I requested a LandXML file from my Civil consultant that looked like this:
I opened that file in Excel and used the Data Connection to create a table with only the X, Y, and Z data of each point (not Breaklines).
I then saved this in a TXT file of comma separated values, that looks like this:
Then in ARCHICAD I used the File > Interoperability > Place Mesh from Surveyors Data... and selected the above TXT file to create the mesh in ARCHICAD (check your tool default layers and settings).
Eli Chiasson
Dexel Architecture
http://www.dexel.ca
AC19-23 USA+MEP • i7-7700 3.6GHz | 32GB RAM • Windows 10 Professional