Help with understanding footings for retaining wall please.

[Gregory01]

Hi all

I’m onto the next project for my house which is to build a retaining wall around the perimeter of my plot to help give some privacy.

Here is an overview of the plot. At the minute I am just looking at completed a-b and c-d..

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• Gregory01
• 3 May 2020

the proposed wall look like this. The smaller wall is at the front (a-b) and the 2m high section is c-d on the plan.

Image

• Gregory01
• 3 May 2020

I am really struggling to understand what I need to do for the footings. The area c-d is retaining as the garden is approx 1m higher than the pavement. It’s currently just banked so nice the wall is build I will want to backfill it to the same height as the rest of the garden.

The wall is 1 brick wide and I was planning on backing this with high density concrete blocks laid flat to give some support to the wall. I’m not sure if this is sufficient so please let me know your thoughts.

for the foundations I was looking at doing a trench fill at 60cm wide and 60cm deep. I was planning on having the foundation filled with 50cm deep concrete. This would need to be right up to the pavement. I would then put the piers of the wall as close as I could do the pavement with the wall sat back slightly as it would be central to the piers.

would someone be kind enough to give their thoughts on if the foundations will be substantial enough to hold the weight of the wall. I am also after feedback on the wall itself - so; it be enough to retain 1m of earth?

Thanks in advance.
Greg

 

[oldbutnotdead]

Structural engineer needed here, especially since your construction borders a public footpath. You may also need planning permission (for what are vaguely called engineering works)
EDIT You may fall foul of Highways if you elevate ground level potentially restricting sightlines on that junction

 

[bernardgreen]

As well as supporting the vertical weight of the wall the foundations for retaining walls have to cope with the horizontal toppling force exerted on the wall by the retained ground. As mentioned getting the advice from a structural engineer would sensible.

 

[Gregory01]

Hi Oldbutnotdead and bernardgreen. Thanks for your responses. Just to clarify the plans have been agreed with the council and Highways so no problem there

Is there a height you think I could backfill without getting a structural engineer involved? The earth is currently at quite a steep bank which is stable so it doesn't appear as though there would actually be a huge amount of unsupported weight the wall would be taking.

Thanks
Greg

 

[John D v2.0]

Yes you would also need drainage so the ground doesn't get wet and get heavier and more liquid causing the wall to fail.a structural engineer is essential here, not just nice to have. I would have thought building control would be involved here.

 

[^woody^]

The ground is already banked, the wall is effectively only retaining whatever you infill which is not a lot, and the load from that is only at the bottom third of the wall anyway.

A 215mm wall in flemish bond as drawn, on 600 x 600mm deep strip will be fine. Drain the back and form weep holes. No need for the extra block wall behind the brick wall

You should start the wall 150 or 225 below the pavement level, not level with it.

 

[John D v2.0]

Personally I'd say you can back fill up to the thickness of the wall with no problems whatsoever. Beyond that it would be a judgement call, from someone with more letters after their name.
I've seen a lot of failed walls due to the weight of the land, so it's worth doing it properly, the cost of an se won't be that much compared with rebuilding the wall.

 

[Gregory01]

Thanks again everyone for your comments. I will see if I can get a quote from a structural engineer.

thanks woody for your comments and I will make sure the wall is started below ground level. Whilst I don’t think there will be a huge amount of weight for the wall to hold back I’m equally sure I don’t want to have to do the job twice. Previous experiences with structural engineers haven’t been great but hopefully this will be simple ish.

 

[mikeey84]

Its about risk assessment. If this was a retaining wall above a farmer's field, then chuck it up, no worries. If it fails, it's a pain in the ar5e, but easy to fix.

A meter high wall on a pavement fails, you could quite easily injure whoever is walking by. Now it failing in that way is probably extremely unlikely, but the consequences are deadly serious

 

[John D v2.0]

That reminds me i must take a photo of this wall next time i go past, it was in much better condition when the street view passed

 

[^woody^]

1.5m high 215mm retaining walls built right, left to dry and harden before loading wont be going anywhere soon and certainly dont "just fall over". The walls are not holding back the whole Barclays bank, just a tiny bit of ground and at a specific part of the wall low down. Ground is not trying to push the top of the wall over like the local yobs

Get engineers involved on retaining walls and you are into cantilever foundations, battering, reinforcement, retaining rods and way over the top design.

 

[John D v2.0]

That reminds me i must take a photo of this wall next time i go past, it was in much better condition when the street view passed
View attachment 191278

As promised - Sadly the worst bit has fallen over/been demolished, but they still left a bit for posterity