The Fun Irish (House)

Hmmm, that's very curious. What kind of soil is it (should be on the report)? Has your BCO been able to throw any light? They usually know what kind of founds are OK in each area they deal with.

 

Assuming no great changes in the local LPA plan - it should be fairly low cost and effort to extend your planning.

I can probably get planning permission a second time as it was granted already. I'll try the building inspector again tomorrow, but his phone has been turned off the last few times I tried. It's going to take a bit longer to get a suitable design and cost more though for sure. As it's in Ireland though I've to reapply from scratch for new planning which is a pain! 

The thing that stands out to me is the 'refusal at 2.6m' - which suggests something hard and amply load bearing (and therefore helpful). You're using Tanners (as lots of people on BH do and given that they're based in Ireland)?

Hope to use them but they have a LONG lead time so went with another Engineer but he doesn't do screw piles or know anything about them so will need to see what Tanners can bring to the table in a month or so. I can definitely dig down to 2m but am hoping a more Engineered foundation avoids this and reduces risk. 

mini piles are cheapest and quickest, need a ringbeam etc.

 

Screw anchors any digger driver can install but they are double the cost of piles. abc anchors can supply quickly, they use https://www.mapl.co.uk/ to design them.

 

 

I don't know the detail of course, but I think the design is cautious.

 

100kN/m2 is perfectly normal and takes standard footings.

70kN/m2 is not great but should be ok. Making footings wider spreads the load and is preferable to taking the whole area out.

 

So I would be proposing standard trench footings at 1.3m.

70kN/m2 is also fine for a floor slab...nobody will fall through, otherwise it wouldn't be safe to walk in the garden. Therefore the ground between footings can stay in place.

 

Yes have  a chat with the BCO.

 

What would be necessary is close inspection of the excavation as it proceeds, perhaps tending higher or lower as the ground is exposed.

Perhaps the SE is avoiding the uncertainty, which some clients would prefer.

 

To be cautious, I would also go with the piles assuming that the 2.6m wasn't just a single lump of something / wait for Tanners to catch up (bug them a bit) / do my planning re-application in the meantime. The latter should just be a case of filing the same docs with a prominent one page note explaining the history. You should be able to download and check the old docs and file them again yourself in an hour or so. Check with your planning officer that nothing has changed and ask nicely for the LPA to process the re-application quickly? Probably other things for you to be getting on with anyway - services?

' screw piles are not common in Ireland,'

 

If you mean the metal ones that are screwed into the ground and left in place, then I am not a fan.

They are ideal for garden sheds, and telephone masts.

 

I discussed these at industry shows some years ago and the reps were giving amazing promises, which turned out to be nonsense.

 

The trouble with conventional piles that are 2.4m long to refusal, is that you then chop the top 900m  off. Very wasteful.

 

UK planning allows anything significant to constitute a start of the works, including forming an entrance. You might chat to a planner about your predicament and see if they allow such a thing, or alternatively what danger of not getting renewal. In UK there would have to be a significant change in the local policy to prevent renewal...and I'm sure you could present it , but the Architect should only charge for a couple of hours.

I'm reluctant to go with piles due to vibration during installation. The close adjacency of other houses is my concern. I'm doubting mini piles would be much better. Any experiences? 

Examining the excavation as we go is an option but may or may not save the day. I was hoping to speak to the ground investigation company but no one returned my call today. 

In ROI you have to have substantial works done to extend, I may well fall foul depending on when I get a new foundation design and book the groundworks team again so I'm studying re-applying myself as the Architect is likely to charge 5-8K as my guess. At least that's my current plan. 

Don't know anything about screwpiles but they appear to tick a few boxes. Any solution for my site is likely to be overengineered anyway but I'm hoping the new structural engineer can come up with something suitable (Tanner) or we can get vibration tests done / more trial holes to determine a safe approach that doesn't rattle teeth or collapse walls! 

And I was worried about last week about finding a plumber in time!! Thanks all! 

What about drilled piles? Thought they weren't too bad for vibration.

 

https://www.self-build.co.uk/piled-foundations-explained/

 

Quote

 

Replacement or bored piles

 

Piles can be either bored or driven into the ground. Bored types physically remove the subsoil spoil, creating a cylindrical tube into which concrete can be poured, so the technique is effectively replacing subsoil in favour of concrete.

 

It is often used on sites that are in close proximity to other buildings as the excavation process

is more controlled, not so noisy and causes much less ground vibration.

 

Boring is frequently used for friction piles as this method suits cohesive and firm soils.

 

However, it’s an expensive option because of the various on-site processes involved.

 

Friction piles could need temporary casings, excavation, management of the spoil, concrete pouring, rebar cage production, insertion etc, plus all of the associated equipment required for handling each process.

 

In terms of excavation methods for bored replacement piling, there are further choices to make. The first option is rotary drilling with a wide bladed auger head, which can remove the spoil as the drill penetrates the ground in a twisting motion (think of a flat bladed cork screw).

 

The second would be a percussion borer that uses a hammer action to drive a tube with a cutting blade through the ground, which then fills with spoil for intermittent extraction.

 

The third is a flight auger, which has a continuous helical cutting blade that removes the full depth of the pile spoil in one process.

 

 

Edited April 11, 2023 by Temp

>>> so I'm studying re-applying myself as the Architect is likely to charge 5-8K as my guess

 

I see no reason to use the architect just to file a copy of the same docs. But even if you did use them, this would only be an hour's work for their assistant. Add an hour if they actually read was they filed last time.

 

I just came across this table in Atkinson for clay soils - it suggests, as saveasteading says that 70-100 kN/m^2 (see column c) is OK i.e. 'stiff clay' for standard foundations. Begs the question of how heavy your design is, of course.

 

 

It's worth getting a few quotes for piling, they varied widely for our job. We ended up with a company owned by a structural engineer, so they threw the calculations in for free and were the most reasonable. There were no vibration issues. Lots of mucky spoil to dispose of tho', so cost that in. 

5 hours ago, mike2016 said:

the Architect is likely to charge 5-8K as my guess

So diy or change. 

 

In case an explanation of basics helps..

There will be a load coming down your structural walls, measured in kN/m.

Say it was 50kN/m and the ground capacity is 100kN/m2, then you make the concrete foooting 0.5m wide. 

But if the capacity is 50kn/m2, then you need a base of 1m width.

 

 

The floor is separate and can sit on much weaker ground.

 

If your project is several stories high, with very big rooms,  then the wall loadings will be very high, and it would become technical and expensive. 

 

Are you sure the se wants to dig out the whole area.? What woild go back in?

 

Plesse be aware that we don't know your circumstances and haven't seen your se report or drawings. 

 

Btw, piles will push through the soft clay very easily.

So my Civil Engineer says there's a lot of "made ground" and we should look at strip foundations to 2.2m rather than Piles. Just needs to be dry and ideal weather etc and we should get this done ok. Next up is to talk to a contractor he knows to see if they are interested. 

I've put a call into the planners to see exactly where I stand on my planning extension request vs where I need to be in the build process onsite and avoid trouble. I'll reapply for full planning if that doesn't look promising. 

Having fun this week with all this!! 

Mini digger will have that out in no

time, it’s finding somewhere

for the spoil/paying for removal that can build up

we had strip foundations dug to 2m on the 'arms' of our build (the bits without a basement underneath) and then put an insulated raft on top like these photos show. it was designed by TSD so maybe give them a chance to come up with a design?

 

Be aware that if you go for piling these can go much deeper than the survey refusal depth. My ground investigation stated refusal at 2.6m, piling contractor quoted to 3m, most went between 7m and 9m! 

 

They charge per linear meter over quoted depth at a cost of £65 per meter for us, we overspent on the piling by £9k! 

 

Bitter pill to swallow but knowing how much concrete and steel went in the ground safe to say it isn't going anywhere!! 

 

We did have the option of 2m deep strip foundation but the cost of getting rid of the spoil meant we just went with piling. 

 

Ours is also 'made ground' but annoyingly, the plot next door 3m from our garage doesn't require piling and they're using a slab foundation. 

 

AD

 

Edited April 12, 2023 by AD1

@AD1 - very interesting that the thing which swung the foundations design decision was the cost of the muckaway.

 

It is possible to put up some rough numbers for the two options you were looking at so we can get a feel for the comparison?

2 hours ago, Alan Ambrose said:

possible to put up some rough numbers for the two options?

Yes but too much work.

If it was in Central London then the muckaway would be expensive. Likewise if it was contaminated.

 

If I had to make a decision now, it would be for trenches. Simply based on experience as designer and contractor.

16 hours ago, Alan Ambrose said:

@AD1 - very interesting that the thing which swung the foundations design decision was the cost of the muckaway.

 

It is possible to put up some rough numbers for the two options you were looking at so we can get a feel for the comparison?

 

The cost of piling quoted was £25,000. (Ended up at £34k with the overspend).

 

That is 34 x 220mm steel case driven piles, construction of ground beam using Pecafill shuttering, concrete and steel reinforcement. Calculations and designed by the contractor and covered by their insurance. All zero rated. 

 

Comparing that to 2m deep strip foundations, we would be paying for:

- Design and Calcs

- Setting out 

- Machine and driver hire 

- Muck away 

- Concrete 

- Reinforcement

 

Sorry I don't have exact figures for the above but at the time my builder did a rough calculation on cost and suggested it would worth going with the piling contractor as a package. At this point I assumed refusal would be at 3m. 

 

The piling is a risk as there is no definitive way to know when the piles are deep enough, so when looking at piling contractors be sure to know what depth is quoted for and the additional cost to go deeper. I've heard some horror stories of piles going down 30m! 

 

What I did learn is that piles are not driven until they stop. They are driven to a pre-determined level of resistance. Unless they hit rock they can keep going until that resistance is reached. 

 

AD

Edited April 13, 2023 by AD1

On 11/04/2023 at 18:03, saveasteading said:

' screw piles are not common in Ireland,'

 

If you mean the metal ones that are screwed into the ground and left in place, then I am not a fan.

They are ideal for garden sheds, and telephone masts.

 

 

any evidence to back that up ?

 

Used on massive infrastructure projects, unless of course you are saying the SE's who design and spec them are wrong and they will fail.

I am saying that the last time I reearched this, they were being used for phone masts and such, which are big-time structures, but not buildings.

The big advantage is in accessing remote locations with everything in kit form.

Also for garden sheds and  garages.

 

I think they may be very useful for portakabins etc. Perhaps also for other modular buildings on poor ground.

 

Not aware of them being economic for habitable, permanent  buildings.

Although they look substantial due to the screw, the central core is quite skinny. Decent strength in the vertical plane but not bending.

 

I looked into using them very seriously some years ago. The reps were saying they were economical for buildings. But analysis showed that we would need enormous numbers of them, so we abandoned the idea.

 

Very happy to hear otherwise.

 

I was keen to try them at first but found that the reps were overselling, and not knowledgable. I think at the time they had obtained rights from Australian manufacturers and were overexcited.

Edited April 13, 2023 by saveasteading

There was quite a good episode of GD on last night on a difficult site with piled foundations that ran into problems. 

1 hour ago, AD1 said:

I've heard some horror stories of piles going down 30m!

Me too. On a site next to one of ours, previously coastal marshland, they completely lost many piles.  They had to put lots extra in and redesign the foundations. 

In case you are worried, we allowed for the very low ground strength and put in enormous pads. The building rises and falls with the tide.

 

Back to the job in hand. There are many types of pile, and the site conditions are known. You should get a low risk quote. 

But piles here should bear at about 3m, and the top m then be broken back, so i still favour strips.  My rule of thumb is to switch at about 2.5m trench depth, but here it is less.

 

Stop press, mike2016 has PMd me a site plan with annotations. There are trees close to the building, so footings have to be deep near the trees. It doesn't change the solution too much.

I don't think we knew about the trees before, but the SE had allowed.

 

Whether the floor can be ground supported is debateable. I think it is unikely to be affected by the trees once encapsulated by the foundation.

Others might want cordek or similar. I would prefer beam and block for simplicity and value.

https://www.screwpile.ie/

 

These guys are in Cork. I have no experience of them however. I think screw piles were actually invented here. 

 

If you do end up with a 2.6m dig I would consider a basement. 

 

Otherwise in good weather you should be able to dig trenches that deep and simply fill them with concrete to ground level. It'll cost more in concrete but it'll be quick. I don't know what the engineering term for this is. Be careful of trenches collapsing. 

 

Typical reading on here has suggested that going direct to a basement company's engineer or a piling companies in house in engineer can save a small fortune as they are much more au fair with the specifics than a general SE.