duel purpose retaining wall

[fourbytoo]

my first post so please go easy on me..!

I have a bank at the side of my house, (which slopes from my border down to my house) which i am currently excavating.
Once excavated i should have approx a 5m x 12m flat space.

The earth is a very heavy clay.

I am planning on having a detatched garage + hardstanding/slab in front of the garage with gates leading to the front garden of the property.

I need to build a retaining wall, about 4-5ft high
I need to build a garage.

I was going to use hollow concrete blocks for the retaining wall,
re-enforced with rebar and poured concrete with weep holes made from drainpipe and cut into though the blocks.

I want to use the same retaining wall (at the far end of the wall) as the lower part of the wall of the garage wall and build it higher without the weep holes and with a tanking membrane behind. Retaining wall will make up two sides of the garage.

before I even get to the foundations stage, can someone offer me advice or opinion.... currently i'm just digging..!

Cheers guys...

 

[freddiemercurystwin]

A wall that high really needs designing by a structural engineer. There have been several threads on the forum where retaining walls have gone over because they're construction was guessed. Retaining wall failures are not so uncommon and one that size will kill especially a youngster. It should be something like this though

to give you an idea though. Build it using a forum for advice at your own risk!

a crude rule of thumb for mass retaining wall is that the depth at the base should be about 1/4 - 1/3 of the height so using blocks lengthways in the depth ie 450 wide would be at least in the right direction.

A reinforeced concrete design as you propose will still need designing.

 

[fourbytoo]

Thankyou for the reply.

is it still possible to use the retaining wall as the bottom part of the garage wall, or do I run the risk of damp problems even with a tanking membrane?

 

[freddiemercurystwin]

There are no problems utilising the retaining wall as the base of your garage wall, you just need careful planning beforehand.

Either an air gap membrane a bit like this http://www.cosella-dorken.com/bvf-ca-en/products/foundation_residential/dimplesheets/products/ms.php

or something like RIW http://www.riw.co.uk/applications/internal_tanking.htm

others may recommend a 'waterproof render' such as Vandex personally though I'd steer clear and go for an air gap membrane.

 

[fourbytoo]

all good info, thanks very much... gives me something to research.