My first project : an automatic 6x8 door/gate/wall, It works with sand and gravel.
Pistons doors are cool but I want a huge door, my goal is something like a 16x30 door.

How it's run :

The sand falls down, is redistributed into two "queues", goes up via two elevators and realigns for rebuild the wall.

This design is still too slow, I'm thinking a new concept now.

It's the first shot for test the idea, very long because of clocks and timers who need some optimization, now it's last 1:10 from button click to wall rebuild. I'm already thinking in a design modification for make it faster.
The design work with a 8x16 wall and i want to make it even bigger, much bigger, but i want to make it faster first.

No mods, only pistons and redstone.

Thanks to Disco for the texture pack and inspiration

If anyone have suggestions or ideas, please leave a comment.

I tried to find if someone did it already with no result.

Sorry for my poor english

Additional Notes

The schematic fits in 4 chunks, be sure to align with chunk for good results.

Size :
Width:21
Length:32
Heigh:39

Up to 700 redstone wires, 350 repeaters and 150 pistons