Any view on retaining wall systems like Allan Block?

19 Mar 2009
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United Kingdom
Hi all. I'm working out what I'm going to do for a retaining wall in the garden (basically the garden is ~1m above the house level and I'm going to take a chunk out (removing existing retaining wall) and make a patio area. The retaining wall will be in two sections; the longest about 4.5m of which 2.5 will be straight and the rest a gentle curve, adding strength. The wall will be about 1.2m high, and the retained soil is clay.

My original plan was to use dense concrete blocks for the wall with suitable foundations, backfill, drainage etc (I've been doing my research!). However I've come across a couple of interlock block systems such as Allan Block (Info is here).

These are about 3x the cost of the concrete blocks I was looking at, but the walls have a simpler construction method and are 'ready finished' so there will be no need to render etc to make the finished wall look nice.

Does anyone have any experience of these systems, or any good advice on whether it's a good or bad idea?

Thanks in advance
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If anything it's overkill for your requirements.

If you install them as per their recommendations it will probably outlast your home.

Even if you decide to go down the dense concrete block route (less attractive IMHO) take extra care to get the back of wall drainage spot on, this is far and away the most important part. It will be a build up of water behind the wall that will cause any cracks etc. as it changes both the density of the retained earth and can alter its angle of repose/friction, making it less stable.

One tip - lnstall a few small dia pipes in the wall - sloping upwards - at a level above your rear drain pipe, they will act like cistern overflow pipes and warn you of a blockage before it becomes a problem.

I cannot vouch for Allan block in particular, but we use this type of block to build underpasses, railway platforms (Luton Airport Parkway Station, if anyone lives around there) etc. The wall is only 1.2m the weight of the blocks should give you an adequate factor of safety against the retained earth sliding, without any need for either steel reinforcing in the wall or ground reinforcing (geotextiles) in the retained earth.

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