AutoCAD Civil 3D :: Iterating Height Levels For A Polyline

I have a problem iterating heights when making a polyline between two different points that have Z-values. I've used Autocad Civil 3D for working with geodetic data with height measurements before and I remember using geodetically measured height values, transforming them into a surface and then when I create a 3Dpolyline within this area the polyline automatically gets z-values that change along the line.

In other words, I could use this 3Dpolyline to obtain a profile that gives me z-values even where there is no exact point with a value has been physically measured. It was a while ago I worked with Autocad and now when I started again I have a similar problem but can't manage to create a surface and get iterated values.

My exact problem this time is:

I have a sewage pipe that runs for several kilometers that is drawn as a 3Dpolyline, with correct x- and y-values. It doesn't have any z-values yet and these are what I want to obtain. I want the polyline to have continuous z-values that changes along the polyline (not only in vertexes) so that a smooth profile can be drawn if wanted. I have data of measured actual z-values for approximately every 500 meters or so along the sewage pipe and these are currently drawn as 3Dpolylines of around 20 meters going perpendicular to the pipe (as in the picture). In other words there are bars with z-values crossing the pipe all along the stretch. Now, what I want to do is to somehow make the polyline that represent the pipe to get the heights from these perpendicular bars with the measured z-values. If I try to draw a new 3Dpolyline between two of the measured bars where the actual pipe is supposed to be, the end vertexes of the 3Dpolyline gets the z-values of the bars. However, the value in between the bars gets the Z-value 0. So, if I start a 3Dpoly on bar 1 then continue the pipe with another vertex, and then finish off at the second bar I will have 2 vertexes with the correct z-value but the middle vertex will be incorrect (0). How do I get the pipe to get the correct z values automatically iterated from the values on the crossing bars? Is this even possible to do? Should I create a surface from the bars first, and in that case how do I do that? If possible I don't only want the vertexes between bars to have iterated z-values, I also want the entire line to have a correct value.

I've attached a crappy image made in paint (since I don't have Autocad on my home PC, only at the office). And just to make things even clearer I'll give an example. Let's say the pipe distance from 1 to 2 is 10 meters, the distance between 1 to 3 is 30 meters and the z-values of bar A and bar B is 10 and 25 respectively. So, when I draw a 3Dpolyline from 1 to 4, I want the vertex 2 to automatically get z-value 15 (since it's 1/3 on the way to B). In the same way, I would like for example the point on the pipe that is right in between 2 and 3 to have the z-value 20. I won't mind redoing the bars to for example singular points instead, if that makes it all easier.