Stop Autocad from connecting and adding segments to polylines I add to a surface

Civil 3d 2011

So I have drawn in my proposed contours along a road

They have been assigned elevations to the polylines and I go to Prospector, Surfaces, Make new Surface "FG", definition, contours, add

I click all my new contours and they show up as a new tin surface but segments have been added automatically and at one point (a low spot) autocad has automatically made the low spot a closed contour where in fact it does close but not at that point.

How do I have autocad just convert my exact defined lines and stop adding things?

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I drew some polylines and made a new surface, added the lines as "contours" they came out 90% what I wanted them too but in a low spot autocad connected two ends of one line and made a oval and on alot of the other contours autocad added segments to them.

Triangulation depends on lots of things number of points the spacing of the points and the pattern of the points (note pline=a number of points) you need to look at the mesh and see where its going wrong a single pt to 3-4 pts is not the same as 4 pts to 4pts ie more triangles. Just taking plines I would look at creating more vertices to see if improves.

This is me thinking aloud but if you are adding lines as Contours, and the line is not a closed loop, Civil needs to do something where the line ends. And as we all know, when you let Civil think for itself, it ends badly....

If you don't want a Surface where the lines are not, then I would look at adding a Boundary as well.

Civil wants to see contours as closed loops, it's sometimes hard to change that.

Would it work better if you added the lines as Breaklines instead?

I merged your threads so that you have all suggestions in one place.

Thanks for the replies but not working. I'm not an everyday drafter, maybe 15 plans a year. Man I wish I could just draw ploylines and use terrain convert polylines like in old versions. Hard getting used to tin surface. In some ways its great, like the autoscaling labels and such, but with I could just draw polylines and have just what I draw be converted to a surface.