Retaining Wall

[antsals]

Good morning all...
I've been trying to sort a retaining wall in the garden for ages but never really sorted it. Anyway I've dug out the area "nearly" and am ready to begin the wall.

From everything I have read the best option seems to be the hollow blocks on a good foundation with re-bar through the holes and then back filled with cement.

I'm building from ground level approx. 1200mm height. Backfill with stone and a drainage pipe around the back of it. I have made a small sketch attached.

Does this sound like the correct option? Is my foundation deep enough? The ground is heavy clay.

How do I hold my rebar inplace while casting my foundation and do I need to bend the ends?

Thanks,
Ant

Wall Section

• antsals
• 4 Mar 2013
• 1

 

[Adrian80]

Maybe a proper SE can tell you,

the rebar sounds over kill, building regs state the wall must be 1/4 of the height its retaining.

I would extend the fondation into the retained side, this would act as a cantilever.

If you reallly want to go down the rebar route you could make a jig to hold it in place, or mix the footing very firm then build a course immediately.

best ask a proper SE though!

 

[tony1851]

Ideally your foundation should extend considerably further forward than the front face of the wall, and the reinforcing bars bent and taken further into the concrete.

This enables the whole structure to be monolithic and shaped like letter 'L'. Any lateral pressure on the wall from behind is then partly resisted by the bearing of the 'toe' of the concrete on the ground.

 

[antsals]

What should I extend the fondation too? Out to 900mm? Does the depth look ok at 200mm? How deep do you think the rebar should be?

Also how do I hold the rebar in-place?

Thanks,
Ant

 

[antsals]

Just updated the drawing.....also this my help but its a horse shoe shape that will help its strength.

Untitled

• antsals
• 4 Mar 2013
• 1

 

[tony1851]

That's it but;
I would go for a slightly longer base (particularly iff the retained soil is not very cohesive);

Make sure there is sufficient concrete cover to the bars;

Overlap the bent bars with some straight ones, to develop the full resistance moment of the concrete.

The curved shape will also help.

Untitled

• tony1851
• 4 Mar 2013
• 1

 

[RobertHH]

Personally I would flip Tonys base around so it projects under the earth at the rear - then the self weight of the earth stops the wall overturning. Also consider that you might need to get the bars bent for you - they're not easy to bend! It could also be done as a gravity wall if you just wanted to lay loads of brick and block, probably about 450-600 wide at its base tapering to 215 at the top.

 

[tony1851]

Personally I would flip Tonys base around so it projects under the earth at the rear

Yes, that is another way, though I presumed the OP would not want the hassle of digging away the earth at the back only to reinstate it.

And yes, if space is not a problem, it might be easier for him to do a gravity wall.

 

[hunggaur]

Hi we just built a massive retaining wall in out garden. We were advised at first to build a canter leavered wall with the extended foundation proportion of the foundation being under the raised section. (The opposite way round to yours) as this way there is an equal downwards force to directional force. In theory the wall cannot fall over as the more force there is pushing forward the more downwards force it creates.

The big issue is drainage and water forces the wall we had to build was 2 meteres high and in the end we went for gabions as it was cheaper than a retaining wall as out SE said the base of the wall had to 900 wide tappering to 300 at the top sitting on a 1.6m wide foundation by 600 deep. Quoted £20k+ for the wall.

The gabions were much cheaper filled cost around £7k and they are free draining so no chance of water pushing the wall over.

May worth looking into geo fabric membranes that you interlace into the wall in 2/3 courses and are then buried into to the slop this stops the wall being pushed over.

Hope this helps

Jon
[/b]

 

[antsals]

Thanks for the great replies,
Its not possiable to dig any further back to lay the foundation the opposite way round. I'd be through the fence aand into the next door garden.

Will it be ok that I dont really have much at the front of the wall? I dont think I can really do downwards much further.

I'll double check my heights tonight and post a few pictures so you can all have a look at it.

Thanks,
Ant

 

[antsals]

I've just sat here all night reading about gabions. What do we all think of them? Is that a better option or not?

Cheers
Ant

 

[hunggaur]

hi Ant

we went with gabions as they were quicker and cheaper.

the ones we got had a separate laying partition at the front which meant we could fill face of the gabions that would be seen which anything we like in our case we used concrete block paver's.

we then backfilled the main bulk of the gabions with broken bricks. from the front they have a nice clean face but the fill was 1/4 of the price of gabion stone.

we had to install 20 meters of 2m high gabion walls which is retaining approximately 1500 tones of soil. total cost was about £7k

i will try to post some photos of what we did later to day if i get chance.

we got ours from fine mesh metals 01902 898208

http://www.weldmesh.com/gabionpricing.php

hope this helps

jon

 

[Norcon]

There was someone on here a while back who used gambions as a retainer.
They were set into a riverbed. Several thousand quid was spent afaik.
The whole lot failed when the river flooded and undercut the base.

The person posting stopped all correspondence with the forum and removed images of the failure for some bizarre reason.
Though I think that was because they had recieved free advice from an SE on this very forum and they didn't listen.

The OP's retainer would be a nice project for 1.2 x 2.7m peri's.
Couple of days work for a wee wall like that a 100 foot long. One were doing at the moment is 200 feet long and 11 foot high. Must be nearly 20 ton of steel in it. 70c/m of concrete have been poured into the foundations.

 

[antsals]

How do I actually calculate what is required.......it seems like a bit of guess work but there must be a simple calculation that allows me to design a wall that is actually suitable.

I'm a mechanical engineer by trade and understand the principles, but how do I come up with an exact number I need to acheive.

Thanks,
Ant

 

[hunggaur]

sorry it has taken so long but here are the photos of the retaining wall we had to put in using gabions below

we faced the front of the baskets where they will be seen with with block pavers and backfilled with brick rubble from the local brick works.

the wall is 2 meters high and 26 meters long in total.

when we built the second layer we set 9 ft long concrete fence posts into the rubble back fill to give us a firm post for our fencing on top of the gabions.

where you can see the brick back fill a building will be built in front of it so it will never be seen

In total it cost about £6.5k some £14k cheaper than standard retaining wall we were quoted for.

cheers

jon

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