buildingconcrete-blockretaining-wall
I'm hoping to use 215mm concrete breeze blocks to build a 20m long retaining wall at 1m high. Do I need to build the blocks on their flat or can it be a regular single skin wall with piers every so often?
The land behind has no structures and the ground is pretty much all rocky parent material covered with about 6 inches of top soil.
I'll be installing a french drain etc.
The blocks you linked to are more for decorative purposes; one or two courses around flowerbeds or trees. What you're going to need for 3'-4' of retaining wall is something like this:
This is engineered block from http://www.anchorwall.com (I'm not affiliated; it was the first thing that came up when I Googled "Retaining wall blocks"). As you can see, they (and most other providers) can put that "hand-chiseled" look on just about any type of manufactured stone, and color it to your liking, so you should be able to get pretty close.
Understand that a wall like the one in the picture will probably run you between 15 and 20 grand, installed. On top of the blocks and the labor, there is a LOT of prep work that goes into building a wall like this. You have to consider grade on both sides of the finished wall, water drainage (water will sink into the soil and collect behind the wall), as well as build a proper foundation beneath grade (this particular wall represents maybe about 20 TONS of stone, so it needs a very solid base of compacted crushed gravel to prevent shifting and sinking). And yes, you need all of this, because if this wall moves, the soil behind it moves, and then whatever that soil is supporting (like your house) will move.
This is about load bearing and claims. The pressure associated with 2 ft of dirt is probably well within the load bearing specification of the blocks in question. 3 feet may not cause any issue, but you cannot hold the manufacturer liable if it collapses and/or if someone gets hurt.
If you exceed the manufacturers specifications an inspector might have a problem with it too. I would recommend adding weep holes, french drains, and possibly a deadman. And since much of the weight comes from moisture, the backfill could be gravel, to improve drainage. In fact there are lots of ways to shore-up a retaining wall, but the onus would be on the "engineer" if something were to fail.
Here's a good picture of some retaining wall features. Source: http://www.fairfaxcounty.gov/nvswcd/youyourland/soil.htm
Edit- A tie back is used on block walls. Screw types and anchor plates are common, but there are probably many ways to accomplish the act of tying or holding the wall in a similar fashion.
Best Answer
It depends on soil conditions. I build on the flat many walls with stable soil behind the wall I build flat to flat no mortar straight up but will back fill with pea gravel or river rock to allow it to drain.
In some cases I will stager each block back a 1/4 or ~ 6mm back this works without mortar with stable ground.
With the above cases for loose soil that may shift I will mortar in place without pillars.
I have seen pillars used and rectangular blocks on edge , it was interesting and much less expensive but I did not think it would hold up as well, I cannot say if it has held up as I haven’t been in that town for years. 1 meter is not a lot but it depends on soil conditions and I like free standing blocks or rail road ties pinned together for small walls so some opinion and some soil conditions make a difference.