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"What hole?"

Nelliekins

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First off - an apology. I've been lax in getting this next instalment posted. Several days away over the holiday season led to several days more trying to sort out family issues, which have since spiralled out of all proportion. I think I have now put the genie back in the bottle, so on with the show.

 

Where were we? Ah yes, we'd poured the basement walls. They'd gone a little wonky (because I was a numpty and failed to install adequate bracing on the outside of internal T-walls), but we had walls that we could build up from.

 

Time for backfill and construction of the remaining foundations (our basement is only 60% of the width of the above-ground house). Before that, we needed to fit a drainage channel around the basement walls & slab. Here's the groundworkers putting the (terram-wrapped) french drain in around the slab/wall junction, which was then covered in 10mm pea gravel to a depth of 500mm, and then 40mm clean limestone:

 

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This actually led to one of the most enduring memories of the project to date. I was laying the drain outside the far corner of the basement (where the cave-in nearly smashed the wall apart). The groundworkers had decided that they wouldn't get in that part of the excavation (between the concrete walls and the bank) in case of further cave-ins, so myself and a couple of mates sorted out the drainage channel. Unfortunately, it had rained a lot over the weekend, and was muddy and slippy and wet... Standing on the edge of the slab was precarious to say the least, and I'm not the most svelte individual... Long story short, I fell into the mud. Which sounds funny, but at the time, it was rather terrifying, because of the depth of said mud, and how much effort it took to get me out of the mud.

 

Don't believe me? Here's how deep it was:

 

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Took 2 people to lift me out of the mud, and I came out without one of my boots as well, which has never been seen since. I had to walk home, because I didn't have a change of clothes, and I had come to site in the Jag. So over an hour, with outside temps being about 3C, trudging home feeling very sorry for myself. At least my mate lent me a pair of boots!

 

One detail I haven't mentioned prior... The basement walls are 10" thick concrete core, but the above-ground walls were designed to be 6.25" concrete core. The mathematically-astute among you will have already worked out that gives 3.75" (or a touch over 95mm in new money). This was intentional, because I figured I was a clever so-and-so, and could use that 95mm as a bearing surface for concrete floor beams. Genius, eh?

 

Well, maybe. It did give us a nice bearing surface, and it did remove a potential cold join between pours at ground level, so big win there. However it then entailed removal of a large amount of EPS from the inside of the blocks so that the beams would slide along on this concrete (because a crane wouldn't get on site very easily, so we used manual labour to move the beams), so the labour aspect was considerable. It took better part of 2 days to remove the EPS (and resulted in about 3 builders bags worth of EPS fragments sitting in our basement), and another 2 days to set the beams in place and start laying the infill blocks.

 

Here are the beams going on:

 

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And here are the floor blocks being laid:

 

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Here you can see the EPS having been removed en mass from where the beams had to slide. Don't worry - it's not a giant thermal bridge, because

 

  1. we put EPS back around the beams once they were in situ properly (albeit much later in this story)
  2. we have now put insulation above the floor beams for the UFH to sit on top of, and
  3. we will shortly be putting insulation under the floor beams in the basement ceilings too (cos we have a load left over)

 

(The big hole is where the stairwell is going, in case you're wondering!)

 

We backfilled at the same time as laying the floor beams. More precisely, because of a battle of wills between the engineer and the groundworkers, we backfilled to approx 50% of depth, then laid the beams (with the walls evenly loaded all round by the backfill to "prevent asymmetric destabilisation and collapse") and finally finished the backfill. 440 tonnes of backfill went in around the basement - that's a lot of stone!

 

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Next up was the remaining foundations. Building Control had specified a minimum depth for the mass-fill RC footings for the rest of the house, because of the massive lombardy poplar trees at the front of site. A nice big strip was dug out (2.5m deep at the front, and 1.5m deep at the back of the plot - furthest from the trees), and filled with concrete.

 

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The engineer had specified cages of 16mm rebar to make our ground beams that linked the mass-fill footings to the basement walls, with clay heave protection, so we dug out from the clay capping over the backfill, formed shutters with the heave protection, and dropped in our cages:

 

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Once the concrete had started to cure in earnest, we laid the first course of blocks on the new foundations, and linked into the basement wall blocks. The steel reinforcement is probably overkill, but better safe than sorry when your engineers starts saying "you don't want the two halves of the house to separate"...

 

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The blue pipes were my attempt to ventilate under the block & beam floor that we were going to lay over the new foundations. Turns out that Building Control didn't care a jot about that once they saw how much backfill stone we had placed - not sure why that would matter, but there you go! Concrete was poured in this course of blocks to stabilise everything, and get us ready to carry on with the build.

 

Myself and a couple of mates laid the remaining floor beams in a weekend:

 

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That'll do for now - as my Mum used to say: "keep 'em wanting more!"

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I can 't emphasise enough what a very dangerous position you put yourself in doing the work between the walls, and the unstable excavations.  Getting up to your chest in mud was bad enough, but if there had been a landslip it would have been curtains.

 

What I want to know, is where the French drain around the perimiter that deep down drains to?  as surely most of the time it will be below the water table so will just sit full of water unless you have piped it somewhere lower or installed a sump and a pump.

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6 minutes ago, ProDave said:

I can 't emphasise enough what a very dangerous position you put yourself in doing the work between the walls, and the unstable excavations.  Getting up to your chest in mud was bad enough, but if there had been a landslip it would have been curtains.

 

Utterly terrifying. I swore out loud when I saw that picture (having thought "bloody hell, I wouldn't want to be working in that gap" when I saw the previous pics).

 

"The groundworkers had decided that they wouldn't get in that part of the excavation (between the concrete walls and the bank) in case of further cave-ins, so myself and a couple of mates sorted out the drainage channel."

 

Sounds like you had sensible groundworkers. Please, for the sake of the people who love you, when a tradesperson tells you something looks dangerous, listen! 

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Agree with @ProDave that you have really put yourself at risk.  Bear in mind that you may be personally responsible if anyone on site is injured and you have not ensured that the work is adequately planned and carried out to ensure safety.  Falls from height is the big one to look out for.

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Made my guts turn over that first picture.

 

 

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Takes me back to when we used to act as casualties for training purposes when people get stuck in mud/sand. When that stuff gets hold of you you are normally in BIG trouble. We all have taken chances when self-building but it is right what people have said above. 

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And if you do get stuck in mud / quicksand, stay still until help comes. The more you wriggle, the more you sink.

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If you get it up over your knees it's near impossible to get out of never mind chest high. 

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Learning point for most places: always have a cheap phone in your pocket to call help when working alone.

 

Do we all do this?

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4 hours ago, ProDave said:

I can 't emphasise enough what a very dangerous position you put yourself in doing the work between the walls, and the unstable excavations.  Getting up to your chest in mud was bad enough, but if there had been a landslip it would have been curtains.

 

I appreciate your concern. To be honest, the risk was minimal - one of the 2 lads helping me was operating as a banksman the entire time, and the collapses only happened in 3 places in the entire 3 month excavation cycle, 2 of which we shored up properly with sheet piles. 

 

The bank had already collapsed at the back, and we had about a week's notice when that went because we saw the cracks forming and propped with acrows, so for the sake of 2 hours of work within the trench, and a banksman watching for new cracks from above, I took the risk.

 

As it happened, there were no further collapses at the back all through the build. 

 

4 hours ago, ProDave said:

What I want to know, is where the French drain around the perimiter that deep down drains to?  as surely most of the time it will be below the water table so will just sit full of water unless you have piped it somewhere lower or installed a sump and a pump.

 

The French drain runs into a sump pit dug beneath the slab, with a 2' square access formed through the slab in the rear light well. The water then gets pumped out using submersible pumps to the combined sewer (with the permission of United Utilities and the council). 

 

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4 hours ago, jack said:

Sounds like you had sensible groundworkers. Please, for the sake of the people who love you, when a tradesperson tells you something looks dangerous, listen! 

 

Agreed. But at the time, they were happy to do it all apart from about 15' of pipe across the back wall. There was no access to get sheet piles installed there, and no other way to shore up the excavation.

 

Plus, there was always plenty of warning when it was going to collapse, which is why we had acrows propping the back up for so long. 

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4 hours ago, Mr Punter said:

Agree with @ProDave that you have really put yourself at risk.  Bear in mind that you may be personally responsible if anyone on site is injured and you have not ensured that the work is adequately planned and carried out to ensure safety.  Falls from height is the big one to look out for.

 

That's why it was just myself and a mate who works in the trade and accepted the risk in the hole. We had mitigate risks with ladders within 6' in both directions to escape the excavation if need be, and a banksman watching at all times. 

 

I am fairly anal when it comes to ladder safety, and my wife is responsible for safety of a lot of people at her work. 

 

We knew the risk, mitigated the risk, and cracked on with the job. 

 

3 hours ago, Onoff said:

Made my guts turn over that first picture.

 

That was the safest place right there... He is between concrete walls and sheet piles - zero risk there! 

 

3 hours ago, Pete said:

Takes me back to when we used to act as casualties for training purposes when people get stuck in mud/sand. When that stuff gets hold of you you are normally in BIG trouble. We all have taken chances when self-building but it is right what people have said above. 

 

The banksman and my mate pulled me out from up top, because there wasn't any way to get me out otherwise! 

 

3 hours ago, ProDave said:

And if you do get stuck in mud / quicksand, stay still until help comes. The more you wriggle, the more you sink.

 

Yeah, I figured that out fairly quickly that day! 

 

2 hours ago, Declan52 said:

If you get it up over your knees it's near impossible to get out of never mind chest high. 

 

I lost a boot, but came out unscathed otherwise. 

 

2 hours ago, Ferdinand said:

Learning point for most places: always have a cheap phone in your pocket to call help when working alone.

 

Do we all do this?

 

I always keep my mobile with me on site, even now. 

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@Nelliekins with a basement being constructed you had a lot more work than most to get out of the ground.

 

How long did it take for the works to take place?

 

Were the works undertaken close to what you expected they would cost?

 

Looking forward to the next entry.

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1 hour ago, Thedreamer said:

@Nelliekins with a basement being constructed you had a lot more work than most to get out of the ground.

 

Certainly did! 😭

 

1 hour ago, Thedreamer said:

How long did it take for the works to take place?

 

We broke ground on 9th October 2017, and the basement was effectively complete structurally as of 22nd December 2017. That's about 11 weeks all told... We were told at the start by the groundworks team that it would take approximately 4 weeks, so quite a difference! 

 

1 hour ago, Thedreamer said:

Were the works undertaken close to what you expected they would cost?

 

Not even remotely. Because the banks were falling back into the hole, we ended up taking out 74*32 tonne wagons of spoil instead of the predicted 52 wagons. We were paying day rates to the groundworks crew, with a 7 week overrun. We had to sheet pile parts of the excavation for a number of weeks, and hire twice as many pumps as we predicted to keep the dig as dry as possible. 

 

We ended up spending 57k on groundworks, and had about 22k in the budget. Our contingency for the entire build was 25k (10%)... I will cover this in more detail in the next blog post, now that we are out of the ground 😬

 

1 hour ago, Thedreamer said:

Looking forward to the next entry.

 

Not long to wait, will try to get it done tomorrow! 👍

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Holy cow, that mud picture!  Glad you're still with us.

 

Hmm, that groundworks figure - I reckon that's about where I'd be if I'd gone with a reduced dig rather than piles for my foundations.  Getting rid of clay is such an expensive business.

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