Retaining wall mechanics change

Instead of individual pieces of the wall, imagine a vertical plane that would designate the retaining wall. It would be build/placed just like conveyors, but the individual wall visuals (corners, wall faces) would be drawn automatically by the game. Player can specify the height above ground.
Basically we designate there is a wall, game paints in the fluff to hide the edge. Instead of having ton of pieces to deal with, we only need one, just like with the conveyors.
The build cost:
Layer 1-4 (9 iron, 30 concrete).
For 5-8 the cost doubles (18 and 60),
for 9-12 it doubles again (36 and 120).
etc.
You can just move one mining square inward (trench benching), and start again from 9 iron and 30 concrete.
Mid game retaining wall recipe for concrete mixer II to simplify logistics, same cost, one piece instead of many.
If materials aren't available to extend the wall, excavators will avoid the spot to prevent the unsupported wall from collapsing.