[ali k]

As there are a few engineery types on here I thought I'd ask for opinions on this.

I'm planning to put external access down into a mid-terrace cellar. There's already a big window with lintel above where I want the door to go so that shouldn't be an issue swapping it. The original retaining wall surrounding the window (to create a lightwell) is stone built (with mortar) and goes almost full height down to the floor level internally.

So obviously I need to dig out and build some steps down, and extend the retaining wall either side of the new path/steps. Asked my gf's brother who is a gardener with landscaping experience how he'd do it and he said hire a mini digger to dig down then pour a concrete footing for retaining walls either side and build double skin wall with block retaining wall and clad in stone to match the original.

I thought this is probably overkill as the original wall is showing no signs of movement, the terrain is completely level not sloping so what they built originally (1890s) has obviously been strong enough. I was planning to just build back the retaining wall with same size stone as the original, biggest stones at the bottom, fully mortared (hydraulic lime presumably?). Height of wall will be just less than 2m.

How would anyone else do it? Gf inclined to just pay someone else to do it but I'm quite keen to have a go.

[Paul B]

One of the largest areas of insurance claims within civil/structural engineering consultancy is for low height (~2m) retaining walls. People have the habit of underestimating them (not realising that loading on the wall increases with time for certain ground conditions, similarly underestimating the effect of retained groundwater). Likewise, insurance covering basement works in consultancy is very expensive. I'd tread very carefully (but then that's probably what any electrician would tell me when I'm considering doing some wiring etc.). Interestingly, a failure on a housing development site came through my inbox recently.

There are proprietary systems that may be of interest (mass gravity systems, reinforced earth even PCC L-walls) although if you had some photos that might help. Some of these systems include 'Design Suggestion' services which essentially means a designed solution without any kind of design liability. Porcupine blocks as an example are pretty darn simple.

Also, if you do undertake it yourself, be very aware of excavation stability and how that changes over time (gets worse), after heavy rain (gets worse) etc. as it's remarkably easy to die in a trench (when you consider material at 1800kg/m³).

I'm not sure what your plan would be for the temporary condition, but if you're removing the lightwell etc. and material surrounding it then you'd probably want to think about it.

Another common thing is seeing something existing and saying that it's 'fine'. All you can say from an observable condition is that the factor of safety is 1.00 (and nothing new should be going in like that). Also, from your description I can't see that a lightwell can fail in sliding whereas a retaining wall definitely can.

Personally I'd be contacting someone with a track record of installing low height retaining structures (with examples that are still standing without issue ~years later).

[teestub]

I’d err on similarly cautious lines as Paul, you may want to check with your insurers first as you are planning on adding retaining structures to your property, so this may affect your policy cover.

If you’re keen to do it yourself then I’d at least be looking at employing a structural engineer to design it for you, that way any issues with the work (if properly completed) would fall onto their liability cover.

Also echo not underestimating how tricky it actually is digging a c.2m deep hole, especially if there’s some non cohesive material, you could end up with a decent amount of spoil.

[mr chaz]

As a geotech I'd echo Paul's comments about how easy it is to die in excavations! If you are going to attempt this yourself the first step must always be to understand the soil and groundwater conditions of the material you are retaining.

[tomtom]

In our house refurbs we’ve had a steel spanning a gap where a wall was replaced. We had a structural engineer do the calcs and drawings for it (£500) and he identified a few issues. The wall under one of the supporting pillars (in the cellar) was actually a wooden door lintel and the existing steel was too weak. Turns out there’s two floors resting on it - and a big roof - with lots of heavy tiles (and snow loads etc..)

He recommended rebuilding the wall underneath with engineering bricks (they’re heavy!) and moving the doorway in the cellar. At first it felt like overkill but now it’s all there, in and with a hefty steel beam it’s the right thing to do.

In other words - maybe get a couple of engineers to come and stroke their chins abs for a few hundred quid you get a proper solution - as the others have said it’s then in their liability.

We had to get ours done - as a building inspector had to sign off on it - but still glad we did.

[mrjonathanr]

I know nothing about engineering Ali but I do know what I don't know (everything) and that makes me very cautious where  failure may have serious consequences.

[ali k]

Thanks all for the replies. I’ve tried uploading pics but can’t work out how to do it - will have another go tomorrow maybe.

Paul - the ‘temporary condition’ is what I’m most concerned about as it’s a relatively tight area I’ll be digging in (front garden) so not masses of space to remove earth either side without going into the neighbours so will be steep banks at risk of collapse while I’m building the wall back up. Not sure how this would be mitigated even with a professional doing it? Shuttering? Acroprops bracing scaffold boards either side?

Not sure what you mean about a retaining wall at risk of ‘sliding’ but the lightwell not. The sides of the lightwell are currently acting as a retaining wall, no? I’m just trying to essentially open it out into more of a ‘corridor’ than a shaft. Would be easier to see in a photo maybe, sorry.

[steveri]

Having just dug out some manky concrete and levelled a base for a shed that was only a few inches out, I can safely say you’ll be removing ‘blummin loads’ of material. You’ll have nowhere to put it and get very fed up of shifting stuff around. Rubble and soil easily trebles in size when you dig it out. HTH!

[cheque]

I’ve tried uploading pics but can’t work out how to do it

Upload your image to imgbb.com (other image hosting sites are available).

Copy the link it gives you for the image.

Start a new reply to this thread and click on the icon that looks like a picture of the Mona Lisa above the smileys.

This will put a little bit of code into your reply- the letters img in square brackets twice, the second one with a slash in front of it.  Paste the code from imgbb inbetween the two.

When you post your image should appear. 

[Probes]

Sounds sketchy to me... 2m depth is a lot of earth to support, and you will need to support it as you dig. It is also a fucktron load of earth to store once out. I dug the foundations for a garage and what came out raised half the garden by nearly half a meter.
Lintel... it goes against most peoples instinct, but a lintel is in essence only supporting a triangle shape of wall above it. I've seen them taken out and the wall above virtually self support. I knocked a 1.5m wide door through the gable end of the house and it was held up by scaffolding boards. So this side of the job I wouldn't be too concerned with. The 2m deep grave I would.

[ali k]

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[ali k]

Fuck me I give up. There's supposed to be a third photo but I can't get it to show. Gives a good idea anyway.

[remus]

It should look like this when you're adding a pic Ali.

Code: [Select]

[img]https://i.ibb.co/1MkTfRm/Photo-3.jpg[/img]


[tomtom]

Hi Ali - I'd be concerned that at the moment the wall parallel to the window braces across the two side walls. If you make the well go further away from the house - you remove that brace. And lets say you make the well with stairs 5 times further away from the window in size - that means those side walls will have to hold back 5 times more weight of material (or more) - without anything bracing across it (if that makes sense). 

Theres also the drain at the bottom.....

[ali k]

I’ve checked the depth of the drain and it’s below the level the floor would be, so hopefully not a show stopper. The downpipe visible in the photo is just from a tiny porch so that could be removed (as others on street have done) and then the only outlet into that drain would be from the washing machine.

Know what you’re saying about the brace though. If it’s gonna end up costing thousands to get someone in even before I start putting a new composite door in I might think again. A lot of money just to make it a bit easier to get pads in and out of the cellar!

[36chambers]

A lot of money just to make it a bit easier to get pads in and out of the cellar!

Could you just replace the window with an angled one that runs over the external hole (so effectively extending the cellar to incorporate the hole). Obviously, adding some framing to cover the sides. If you could install a window that opens up, like a car boot, then you could just hurl the pads in and out.

[teestub]

Was going to say similar, if it’s a case of just wanting to get things in and out you could just change the window for something that opens fully so you can put stuff in the light well, or extend the window down to near floor level and put a larger opening in without the steps. Obviously won’t be as accessible but would save a lot of groundwork and expense.

[Paul B]

Lintel... it goes against most peoples instinct, but a lintel is in essence only supporting a triangle shape of wall above it.

This is correct. Some good info/diagrams here (and a nifty bit of kit):
https://www.brickbrace.com/

Also, there's good knowledge on bulking effects. 3x isn't an unusual number.

Paul - the ‘temporary condition’ is what I’m most concerned about as it’s a relatively tight area I’ll be digging in (front garden) so not masses of space to remove earth either side without going into the neighbours so will be steep banks at risk of collapse while I’m building the wall back up. Not sure how this would be mitigated even with a professional doing it? Shuttering? Acroprops bracing scaffold boards either side?

You've got two temporary issues there, your excavation being one (and the knock-on effect of removing material near to your neighbour's boundary), the other being that your house is used to having material in front if it that you're planning on excavating. The footprint of your excavation might end up being wider than you're envisaging by the time you've constructed a footing etc. Generally old structures don't like changes to loading.

Not sure what you mean about a retaining wall at risk of ‘sliding’ but the lightwell not. The sides of the lightwell are currently acting as a retaining wall, no? I’m just trying to essentially open it out into more of a ‘corridor’ than a shaft. Would be easier to see in a photo maybe, sorry.

Essentially what TomTom said; yes, but they're relatively short and they're propped by the side that runs parallel to your house. Any retaining structure wouldn't have that prop. What I mean by sliding is the whole thing displacing laterally.

[ali k]

Several houses on the street have done what I was hoping to do so I might ask how they managed it before I give up on the idea.

Though I expect they might have just botched it like I was wanting to do. Access would be for bikes too so not sure the hatch window thing would cut the mustard for gf.

You bloody geotech gloomsters…I was hoping for some Boris-style optimism to spur me on instead of all this sensible talk! 

[ali k]

Had a chat with a couple of mates today (builder and ex brick layer) and they concurred with everything already said on here. Much bigger job than I’d anticipated. Will discuss with gf to see if we think it’s worth pursuing or not.

Thanks for the replies - and thanks for sorting the photos Remus.

[teestub]

Sorry we couldn’t have had a more red white and blue can do attitude 😄

[Paul B]

Had a chat with a couple of mates today (builder and ex brick layer) and they concurred with everything already said on here. Much bigger job than I’d anticipated. Will discuss with gf to see if we think it’s worth pursuing or not.

You still might be able to get a Struct. Eng. to come and quote for the work (or take loads of photos/videos for them instead) and give you a better idea of what's involved (or what's involved to achieve the function you're looking for)?

I was chatting to Peewee the other day and someone was having to arrange £400 crane hire for a day as they'd misjudged the width of a newly acquired hot tub / sex pond and needed to lift it over the house instead of getting it past the side 

[abarro81]

hot tub / sex pond

[Reprobate_Rob]

I was chatting to Peewee the other day and someone was having to arrange £400 crane hire for a day as they'd misjudged the width of a newly acquired hot tub / sex pond and needed to lift it over the house instead of getting it past the side 

Peewee has a sex pond?
(and can't use a measuring tape)

[Probes]

I was chatting to Peewee the other day and someone was having to arrange £400 crane hire for a day as they'd misjudged the width of a newly acquired hot tub / sex pond and needed to lift it over the house instead of getting it past the side 
[/quote]

This has made my day, on many levels.