Converting 3D Faces to a single Surface (or Polyface Mesh)

Before you say, "This issue has been addressed", please read through my problem, and then decide/respond.

I have created a TIN (triangulated irregular network) of an existing survey in my terrain modelling software (12d Model). I am able to export (save-as) the TIN as 3D Face Triangles for opening in AutoCAD (2012) or similar.

My ultimate goal is to create a solid surface in Inventor. The surface has to be seemless (stitched) in order for me to create a new sketch and extrude to this surface. Finally giving me a part in Inventor that represents my ground. I would then want to use the same process to bring into Inventor all other Civil Design works created in 12d Model such as roads, earthworks platforms (including dams) etc.

I've tried stitching (Inventor and Microstation) without success. Inventor keeps crashing and Microstation looses data.

AutoCAD (2012) won't let me create a polyface mesh from 3D Faces. I tried doing a mesh, surface union without success. Programs either crash or data is lost.

Can anyone help?

12d Model > AutoCAD > Inventor? And this is for a "civil" design. It begs the question...why aren't you using a program like Civil 3D in the first place? Civil design in Inventor just doesn't seem like a good fit to me.

Maybe this will help?

http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=13219673&linkID=9240617

Re: Inventor 2013

"Autodesk® Inventor® 3D mechanical design software includes CAD productivity and design communication tools that can help you reduce errors, communicate more effectively, and deliver more innovative product designs faster."

Does this sound like a program geared to civil design?

Thanks ReMark,

I need this to provide our mechanical drafters/Inventor modelors with my civil design in an ongoing process, keeping the terrain Part up to date with relevant earthworks, and road data.

I will apply your advice in the sequence u advised. I've tried it before, but not as suggested. Will keep u posted.

Earth works, road data and Inventor, in my opinion, is a poor match-up.