concrete block retaing wall

[iceman2013]

Hi all i really need some good advice please , Im building a wall in my garden after digging out some of my garden that slopes up and away from my house to extend the size of my patio.

Im going to use 100mm solid concrete 7n block and then have it rendered the wall is going to be 4ft high by 23ft wide there will be stairs in the middle and smaller walls either side about 2ft high going back towards the house,

Do i need to build piers into the wall as additional strength?, will the 100mm blocks im using be ok single skinned, ive dug footings to 300mm deep (150mm hardcore and will have 150mm concrete) by 300mm wide is this ok,?
The soil under the footing is clay type soil

What sort of drainage do i need what ratio for the concrete footings would you recommend

Read more: //www.diynot.com/forums/garden/garden-retaining-wall.369332/#ixzz2XhKmri37

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• iceman2013
• 29 Jun 2013
• 2

Untitled

• iceman2013
• 29 Jun 2013
• 2

Untitled

• iceman2013
• 29 Jun 2013
• 2

 

[munchingB]

hi, i work with landscapers sometime and im under the impression that you need a slightly more engineered wall if youre retaining anything over 1 metre high. i think there is a bit more to it than just building a conventional wall as ive seen similar builds where the back face of the wall has had a much larger footprint with double the thickness at the bottom then sloping 45 degree to the top of the wall. ive seen them infilled with concrete and all manner of membranes and layers of gravel etc to allow drainage..

 

[freddiemercurystwin]

As mentioned above, anything approaching the kind of height you are talking about you really need to to consider professional advice. Anyways, a crude rule of thumb fpr mass retaining walls is that the depth of the wall at the base should be 1/4 - 1/3 of the heights so @ 1.2m high the depth should be at least 300mm or 3 blocks thick getting thinner as you go up. Your single skin of block will likely just fall over. Your foundation is too small aswell, you should double the width of it. Adding a couple of piers is not really appropriate.

Here's one I did earlier although this was stone clad but that makes little difference:

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• freddiemercurystwin
• 1 Jul 2013
• 1

 

[freddiemercurystwin]

Also, why have you lined the bottom of your trench with rocks? The foundation should be cast on earth.

 

[iceman2013]

the rocks have been crushed and compacted into the soil to form the hardcore base for the concrete to go on top of.

In your diagram are the concrete blocks layed on there sides?

Thankyou for the help and advice it is really appreciated.

 

[freddiemercurystwin]

the rocks have been crushed and compacted into the soil to form the hardcore base for the concrete to go on top of.

In your diagram are the concrete blocks layed on there sides?

You don't put hardcore under foundations, they rely on sitting on undisturbed earth.

And that's not hardcore btw its as you say compacted rocks, not the same thing.

Yes the blocks are on their sides. In theory it doesn't make any difference, its the mass of the thing holding the earth back.

 

[i_am_fubar]

//www.diynot.com/forums/garden/garden-retaining-wall.369332/

 

[Deluks]

Looks to be retaining about 800mm from that first picture, hollow concrete blocks will do it, rebar and backfilled with lean mix.

 

[iceman2013]

Im getting mixed info ive widened my footings to 600mm wide and there 300mm deep, i was told by a builder that you should use hardcore first in any foundations, ive now also been told i should increase the depth aswell another 9 inches ?

mega confused by all the different opinions im getting

help!!

 

[freddiemercurystwin]

Your builder is not a good builder and I would suggest you take no more advice from him!

The reason has already been stated in this thread but see for yourself, find a detail amongst this lot where hardcore has been laid beneath the foundation: https://www.google.co.uk/search?q=f...urce=og&sa=N&tab=wi&ei=Th_UUfjhB8KShgf8uoDwCw

Going down another 9" is pointless IMO.

 

[iceman2013]

Right so get rid of the hardcore then, and lay my concrete foundation on the soil. shall i still go with 150mm depth and 600mm width of concrete then

once again thanks for all the help so far.

just found this though
http://www.self-build.co.uk/groundworks-foundations-0

 

[limerockconstruction]

FMT has got it cock on....

For an 800mm wall pour 250mm of concrete on undisturbed ground, lay 4 courses on flat and then add a couple of up right courses. Jobs a good un, thanks to FMT and goodnight!