joining of the 2 skins adds strength but a single bound together wall with no ties would be stronger
Hence the need for a 9'' block wall and facing brick.
For example If your were rendering the wall instead of using brick you could have it 13'' block for the first 18'' of height then 9'' up to the top.
You could almost get away with just 9'' block work on its own but not quite in my opinion which i why the 9'' blockwork plus brick skin will give a wall that is strong enough and deal with the staining problems associated with retaining walls using brick.
the 13'' block work is just required to get you out of the ground as its quicker and cheaper to lay than starting your nice brick just to bury 4 courses of them.
You can alternatively bring your concrete up to nearer the surface by making it much thicker and start immediately with the brick and block but you'll need to work out whether that is cheaper than buying the extra blocks. Its obviously faster but if your DIY'ing the cost is perhaps more an issue.
By all means repost a simplified question regarding heights and wall thickness in the building forum and get some more opinions as some may think a 9'' wall is fine.
Personally i work by the rule of 600mm is the max retaining wall height for just 9'' blockwork
Hence the need for a 9'' block wall and facing brick.
For example If your were rendering the wall instead of using brick you could have it 13'' block for the first 18'' of height then 9'' up to the top.
You could almost get away with just 9'' block work on its own but not quite in my opinion which i why the 9'' blockwork plus brick skin will give a wall that is strong enough and deal with the staining problems associated with retaining walls using brick.
the 13'' block work is just required to get you out of the ground as its quicker and cheaper to lay than starting your nice brick just to bury 4 courses of them.
You can alternatively bring your concrete up to nearer the surface by making it much thicker and start immediately with the brick and block but you'll need to work out whether that is cheaper than buying the extra blocks. Its obviously faster but if your DIY'ing the cost is perhaps more an issue.
By all means repost a simplified question regarding heights and wall thickness in the building forum and get some more opinions as some may think a 9'' wall is fine.
Personally i work by the rule of 600mm is the max retaining wall height for just 9'' blockwork