Maria

Retaining wall options

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We are about to start a build of  a dormer bungalow in the corner of our garden. The back  of the build will be next to an embankment, that would need partial excavation to accommodate the patio. The finished height can be anything up to 3 m (I assume) and 17.5 m long . The embankment is various heights (the highest point is about 5 m) at different points and just a bit of empty land - about 10 m deep that doesn't have any traffic or neighboring properties, so we can excavate into it and grade it down to required height, I assume. I have attached the site section.

 

Nothing was specified in the building regs and I understand that we can opt for pretty much anything as long as it's structurally safe. Our major issues are tight access and budget constraints. We won't be able to get any large machinery on site: the biggest lorry that can get in is 3, 4 tonne. The nearest parking point for cement mixer/larger machinery is about 40 meters away, so any concrete would have to be either pumped or brought in by dumber trucks. The cranes are probably out of question as well, so any large, heavy items like steel beams would be difficult and extremely expensive to get on site.

 

What would be our best options? I was thinking along gabion baskets and perhaps recycling some of the excavated material, as it's quite rocky. Is this something that can be done ourselves to save costs? I've had a quick look and there are online calculators for required width and stone volume. Do we need SE report for this?

 

Any other suggestions? We basically need something that's not too expensive and feasible.

 

 

Retaining wall.pdf

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Welcome.

 

We also had to build a big retaining wall behind our build, so I went through a fair few options, including gabions.

 

The key questions are: how much of the sloping land behind where the wall will go is going to remain yours?  and will there ever be anything close to (within about 5m or so) of the top of the retaining wall that might increase the imposed vertical loads behind it (things like a path, driveway, outbuilding etc)?

 

The reason the first is key is because public liability kicks in if that sloping land behind will be owned by someone else, and that makes a significant difference to both the approach taken and the cost, given that the retained ground is higher than 1.2m.

 

The second question just relates to the loads that are imposed on the wall, and impacts the forces the wall has to withstand, so affects the structural calculations a fair bit.

 

If you are retaining ownership of the sloping land behind, then gabions or permacrib are both good options, probably the cheapest way to build the wall with the least amount of machinery.  They are not space-efficient, though, as a gabion or permacrib retaining wall that's a couple of metre high will be well over 1m, thick at the base, and will take up a lot of space, as it has to slope back with a slight batter angle in order to resist the overturning forces.

 

Somewhere I have a spreadsheet I used for doing all the calculations for gabions, to the current Eurocode, that might help, but before going any further knowing who that land belongs to and what other loads there may be imposed is needed.

 

There are also shaped interlocking dry block systems around, Stepoc is one and there are probably a handful of others.  They are all gravity retaining walls, like gabions, and usually the manufacturers have standard designs, although you do need to know the bearing stress of the soil, plus a few other characteristics before any design can be done that needs to be signed off officially (for example, for house insurance).

Edited by JSHarris

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1 hour ago, Maria said:

We are about to start a build of  a dormer bungalow in the corner of our garden. The back  of the build will be next to an embankment, that would need partial excavation to accommodate the patio. The finished height can be anything up to 3 m (I assume) and 17.5 m long . The embankment is various heights (the highest point is about 5 m) at different points and just a bit of empty land - about 10 m deep that doesn't have any traffic or neighboring properties, so we can excavate into it and grade it down to required height, I assume. I have attached the site section.

 

Nothing was specified in the building regs and I understand that we can opt for pretty much anything as long as it's structurally safe. Our major issues are tight access and budget constraints. We won't be able to get any large machinery on site: the biggest lorry that can get in is 3, 4 tonne. The nearest parking point for cement mixer/larger machinery is about 40 meters away, so any concrete would have to be either pumped or brought in by dumber trucks. The cranes are probably out of question as well, so any large, heavy items like steel beams would be difficult and extremely expensive to get on site.

 

What would be our best options? I was thinking along gabion baskets and perhaps recycling some of the excavated material, as it's quite rocky. Is this something that can be done ourselves to save costs? I've had a quick look and there are online calculators for required width and stone volume. Do we need SE report for this?

 

Any other suggestions? We basically need something that's not too expensive and feasible.

 

 

Retaining wall.pdf

 

1 hour ago, Maria said:

We are about to start a build of  a dormer bungalow in the corner of our garden. The back  of the build will be next to an embankment, that would need partial excavation to accommodate the patio. The finished height can be anything up to 3 m (I assume) and 17.5 m long . The embankment is various heights (the highest point is about 5 m) at different points and just a bit of empty land - about 10 m deep that doesn't have any traffic or neighboring properties, so we can excavate into it and grade it down to required height, I assume. I have attached the site section.

 

Nothing was specified in the building regs and I understand that we can opt for pretty much anything as long as it's structurally safe. Our major issues are tight access and budget constraints. We won't be able to get any large machinery on site: the biggest lorry that can get in is 3, 4 tonne. The nearest parking point for cement mixer/larger machinery is about 40 meters away, so any concrete would have to be either pumped or brought in by dumber trucks. The cranes are probably out of question as well, so any large, heavy items like steel beams would be difficult and extremely expensive to get on site.

 

What would be our best options? I was thinking along gabion baskets and perhaps recycling some of the excavated material, as it's quite rocky. Is this something that can be done ourselves to save costs? I've had a quick look and there are online calculators for required width and stone volume. Do we need SE report for this?

 

Any other suggestions? We basically need something that's not too expensive and feasible.

 

 

Retaining wall.pdf

Hi Maria

 

i think a structural engineer is a must Get a few quotes 

For a small anount of money it will give you piece of mind

and he or she may think of an option that you hadn’t considered 

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Good plan to use a structural engineer, but shop around for quotes.  We had quotes from over £4000 to £300 for our retaining wall design by a structural engineer.  Needless to say we used the chap that was £300!

 

If you want some idea of the design work that went into our retaining wall, these blog posts illustrate the size and complexity of it.  In total we removed around 900 tonnes of earth............

 

http://www.mayfly.eu/2013/07/part-six-there-we-were-digging-this-hole/

 

http://www.mayfly.eu/2013/07/part-seven-pouring-concrete/

 

http://www.mayfly.eu/2013/07/part-eight-the-wall/

 

and these are the drawings and calcs we got from our structural engineer:

 

20717.pdf

 

20130228093748130.pdf

Edited by JSHarris
typo

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We paid a few hundred for our SE calcs, certainly wouldn't have done it without SE input, far too important in our situation, if it failed it would come down on the house.  We had to build a huge retainer right around 2 sides of our plot as house is sunk down and double expense as we wanted a separation between retaining wall and house (we have only 1m at closest point of house to wall)  I didnt want house into bank but the retaining wall does form two sides of the garage,

 

We used blocks and concrete and steels and drainage in the bottom.  We are retaining about 3m of earth and the wall rises about 3m high beyond that.  We did the side that is facing our neighbours garden in brick but our side is block and we will render that. We are on horrible clay.

 

I have pics I can post if any use.  I know the whole thing cost about 25k and we have not rendered our side yet. SE was the cheapest part of the operation!

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6 minutes ago, lizzie said:

 I know the whole thing cost about 25k and we have not rendered our side yet. SE was the cheapest part of the operation!

 

Same for us.  The wall ended up costing well over £30k, by the time it was rendered our side with a stone wall added on top for the neighbour, with a fence above that.  The SE cost was pretty trivial in the overall scheme of things!

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Hi all,

 

Many thanks for your feedback, which is really appreciated. The land behind is ours and there will be nothing there. I suppose, we'd have to allow for occasional foot traffic by occupiers of the newly built house, as there is currently access to the top of the embankment ad we intend to keep it. 

 

I will try to try to contact a few engineers tomorrow, and hopefully can find someone for under £500.

 

The total cost of £25-30K scares the hell out of me.

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Do you need a big retaining wall, or can you terrace that bank instead?  Terracing, with walls not exceeding 1.2m, significantly reduces the work needed, and below 1.2m a retaining wall can be a standard design, reducing costs still further.

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I used one of the dry stone systems to hold back my driveway. It doesn't need a concrete base but you can put one in if you want. It's very simple to build, the blocks have a lip at the back edge so you can really go wrong. My wall at its highest is 1.6m so I had to use the larger blocks. 

The other smaller walls in the pic are made with a much smaller block but you can't go higher than 1.2m so as Jeremy suggests I used two walls with decorative some in between to get me the height I needed.

There is near 30m of wall and it cost approx £2000 over 3 years ago. This is where I got it from.

https://professional.ag.uk.com/products/retaining-walls/anchor-diamond

It goes to a max height of 3m with the use of a geo grid. Screenshot_2018-01-10-21-31-07-991_com.google.android_apps.photos.thumb.png.fc6128b5c6bf7be26854708cba3a5288.png

Edited by Declan52
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15 hours ago, JSHarris said:

Do you need a big retaining wall, or can you terrace that bank instead?  Terracing, with walls not exceeding 1.2m, significantly reduces the work needed, and below 1.2m a retaining wall can be a standard design, reducing costs still further.

I would prefer to have it terraced. This way, I think we'd get more use out of this bit of land. So will check with the builder. I assume we wouldn't need to get council approval for it?

 

Thank you for the link and photos, Declan. Will give them a ring in a moment.

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The only need for a change to your planning approval, AFAICS, is if it includes an approved landscape plan, with details as to exactly how you are going to landscape the garden.  The latter is really only important as far as the VAT reclaim goes, as you can only reclaim VAT for garden landscaping if it is part of an approved landscape plan in your planning approval.

 

I would think that even if this was in your planning approval it would only be a non-material amendment, anyway, so shouldn't be any real hassle to get changed.  Worth getting the planners to include the landscaping as a planning condition usually with a garden like this, as getting the VAT back is very useful on the relatively high cost of this type of work!

Edited by JSHarris

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0ur site was not  as challenging as yours appears to be but our plot does rise over 3m from the front boundary to the rear and slopes from right to left, looking up from the front. We had a lot of existing shrubs, trees and hedges that we wanted to retain  from the existing house and the landscaping had to deal with this and the slope. We could not get our head around a decent design and engaged a landscape designer to produce a design. The landscape design  wasn't cheap but my OH (who is the garden expert) insisted on it. In the event it was money well spent for the following reasons:

  • As @JSHarris recommends, it allowed us to incorporate the landscape design in the Planning Application, though it was never  included as a Condition in the Approval. All the work was VAT exempt from our contractor
  • It allowed us to get good cost estimates and manage the work, with the groundwork contractor responsible for the ground clearance, hard landscaping, underground services and base for the passive foundation,.
  • It allowed us to plan all the critical ground clearance and landscaping work that had to be completed with the heavy equipment before the foundation and underground  scope was started. There was no way that we could have attempted this work after the house was built, as we could not any big equipment onto the site, except a  small digger and it would been a long and laborious job.
  • It minimised the amount of material that had to be taken off the site and eased the lorry movements (we had 69 lorry movements for this part of the project), which was important to us as we are opposite a school  on a busy road and we wanted to have minimum impact from our build on the neighbours, including the school. In fact, we planned the major groundworks, including all the hard landscaping, except finishing the terrace and drive with paving slabs and Suds blocks, to be be executed in the school summer holidays. It was  4 weeks for the groundwork contractor and another week for MBC to install the passive slab.
  • It allowed my OH to plant the garden  before the house was finished, though the lawn elements were left until later.
  •  

I believe that key for you is to get some ideas on landscaping including the retaining walls/terracing that meets your needs,  incorporate the landscape design  in your Planning Application/Approval and then it will give you a good starting point  to execute it in the most effective manner as part of an overall plan for your project.

Groundworks Day 1_20.JPG

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2017-10-27_12_32_58.jpg

Edited by HerbJ
typos and tidy up the text and intent
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Thanks again for your input...

 

Herb, your garden looks amazing! 

 

I think we'll be planning to terrace the embankment.  This way we might be able to avoid taking a lot of muck off site as well. The embankment is at the highest point behind the build and we can potentially redistribute the excavated earth to build up the levels further away. The architect confirmed that we don't have go through planning for this. We just need to see if we want to get an approval in order to claim VAT back as you, guys, suggested. 

 

Time might be an issue though, as we bought the plot with the planning permission already in place, and it runs out end of May, beginning of June.

 

 

 

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pm me and I will send you some other documents to give you some better idea of the landscape design drawings. They were't very detailed but enough to incorporate directly onto then plot plans and elevatton. We then  prepared  drawings for the groundwork contractor, using a building design technician and SE for the retaining walls

 

Use the time, if you can manage it. Time spent planning at this stage will save you £1000's in execution and potentially give you a more usable garden space.  You may be able to make a "substantial start to construction" to make your existing Planning Approval extant and then you have lots of time to do what you need to do. This is what we did with similar timeframe to you after we bought a house with Planning Approval. We completed the purchase of hour plot at the end of July 2014 and the Approval was due to lapse at the beginning of November 2014. We submitted a complete new planning application for a new house design without any concern for the original approval lapsing. We demolished the existing house using the original Approval in February/March 2015 and started our ground works on 24 July 2015, after getting Approval for the new design.

 

 

 

Edited by HerbJ

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On a previous house we needed a retaining wall aprox 3m high and found out that any structure used for retaining would require engineering drawings if over 1m high, 

so we built 3 terraces all aprox 900mm high with a very light slope aprox 3m wide and built timber planters on the relatively flat bits and turned it into a veggie garden, it worked very well as each flat area was sheltered by the one above. 

 

Just bear in mind a group of terraces will take up more land than a vertical method. 

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