If this wall is going to have any surcharge on it you need to grid it, the keystone,versalok,diamond is the cheapest and best way. don't backfill w/dirt you need clean 1" angular quarried rock, not rounded river rock, behind it. at least a foot of it all the way up and then your dirt. these walls bleed off hydrostatic pressure but they need the rock backfill to work. the block with the lip on the back assemble faster than the pinned block and have more setback per course, if there was no surcharge on top of it i would assemble it w/lipped block, glue the whole thing together, get the first course 2" subflush to grade on a compacted crushed rock base. the block run about 5$ a sq. ft here in STL. dont use less than a 6" block, if you use the conc bag method you will have one trashy looking mess.

 

I agree. If you are dead set on doing it with concrete bags build a footer and cure the bags first. Then set them in mortar. It will be much stronger. As far as the engineering goes you are on your own as to if it will last or not. Generally speaking stick with known construction standards.

 

The wall will be 3 sided, shaped similiar to a U, so I'm thinking that it will stand at 7 ft without falling. What is the avg life expectancy of good used railroad ties? I'm trying to do this without spending a small fortune I don't have access to any rock in my area unless I want to buy by the dumptruck load and it ain't cheap.