Originally Posted by
journeyman Mick
Al,
don't you mean 390 x 190 x 190 blocks? You'd need to talk to an engineer of course, but my gut feeling is that you'd need 16mm or larger Y bar, at least in the bottom half. I'd also recomend you use a silasec and cement mix painted on the inside to waterproof over which you can also paint a bituminous coating. I reckon you'll need a 250 x 250 slab edge thickening with a couple of Y bars in it. Definitely worth checking with an engineer to save an expensive (and embaressing) failure.
Mick