I'm a mechanical engineer and i work in construction area. Currently i'm working in a dam (barrage) in portugal, and i can't do measure of massproperties (volume) of an block (concrete).

I need to calculate all the volume of concrete that i need to do that block. 

What i do is, copy the bonderies of the dam and paste on side of the real draw (you can see in drawing). Because the growing of the dam is not equal (the width and lenght is not the same in every block) i need to use the loft to calculate the volume. But first i need to erase all the surfaces that growing on his sides. I erase all surfaces and calculate the gross volume, and then, separatly i add all the exterior surfaces.

But, i think that i'm doing something that is not right because i do the EXPLODE the polylines, and then SKRETCH to  intercept the two sides. I think that when i do the skretch to unite the polylines is not follow the path, and with the loft can see that the grid is not the same (please check).

There must be another way to unit the two polylines to follow the path. I tried to get the angle of the arc of the side the dam, and made a new arc, instead put together two polilynes. But i cant get the radius.

I Attached the file, but have more than 500kb.  Coud you help me? I really need help to make the measuring. Please