scheme is to pile thro’made ground’ approx 8m deep using vibro compaction stone piles just abandoned this method on shallower made ground site gone to driven steel casing. dont want to get mugged again so any real life successes going to this depth or beyond?
thanks

what size of project ? domestic or commercial?

Driven PCC usually cheapest option.

Vibro compaction or CMCs can be used in shallower depths than precast piles, I think. My experiences with vibro compaction on commercial sites has always been more straightforward than precast or CFA.

8m depth is no real depth for a pile however an end bearing driven pile will need a stronger strata to bear upon than you will get away with than with vibro ground improvement / vibro stone columns. Even skin friction piles will be probably slight greater length than vibro to get enough decent ground for enough skin friction.

It comes down to thickness on quality of the made ground and the depth to, and strength of, the underlying natural strata you will bear upon.

Im assuming you have a GI report?
EDIT:
Re-read OP x are you asking for success of vibro to >8m? If so yes max is generally considered to be 12m ish in normal setting but your vibro contractor should be able to advise. Really depends on the make up of the made ground and what’s under it.

Without knowing specifics, I would go with whatever the person who is liable for your foundation design recommends, (after appropriate due diligence).

Marcus +1

There’s a lot more to consider. Is the made ground contaminated? How big is the load? How much uniform settlement is tolerable, how much differential settlement is tolerable, what is the sensitivity of the area to driven pile noise and vibration? Probably more, that’s just off the top of my head.

thanks chaps,
I get all of the above and have struct engs ,borehole logs etc just wanted to get a feel for likely possible depths providing ground is suitable.
Did a few trial pits yesterday to 8 m still in made ground! Looks like vibro ok may need preboring £££,. current site made ground too loose to fully compact columns stone migrate into the sh..e now gone to driven £££ we are .getting there.and still in work

This does all sound very complicated and technical, suffice to say, I’m swooning at your collective cleverness 😉

Whilst I’m not a geo tech, nor do I do piling on a day to day or even infrequent basis, I did have some piling done about 5 years ago to provide our existing boathouse here on the Norfolk Broads with a more stable platform. The wooden and thatched building measures 17m x 8m, so of a reasonable size for a wet dock boatshed. When I asked the contractor how deep would they go with their steel tubes, he said until they get less than 10mm deflection ( it might not have been ‘deflection’ but basically I assume you know what I mean?).

So for a given weight dropped repeatedly from a given height, they keep going until the tube is essentially held by friction, as the hard ground in this part of the country is quite some way down. As you all probably know.

Anyway, in total, 10 pairs of piles went to a depth of between 13m and 17m.

Which is not the answer you’re looking for, however, I kinda liked their gut feel and experience of the locale approach.

jag61, what is the nature of your project? Crucially what will be the value of the structure and value/revenue/criticality of the operations/activities it will accommodate/undertake?

What would be the impact of ground movement on the structure/contents/machinery/operations?

Even if you have had reports by geo-techical engineers, be extremely wary of placing reliance on any assurances that future movement would be limited to a given maximum: I would expect any expert to limit their potential liability if they are proved wrong by careful caveats in the report, and even if they were liable, the amount of any Professional Indemnity insurance cover they may have may be only a fraction of the potential losses.

Lastly, if the above is not enough to make you think again and deter you, I would add that you should not be surprised if you/your employer/client finds it impossible to get insurance cover for subsidence. Even if they were lucky and found that their insurer would give cover this year, the annual nature of insurance contracts means that that could easily change at renewal.

TL;DR

Don’t do it unless it’s very low asset value/revenue generation/criticality.

8m of made ground? yuck, that sounds frankly horrid and would be making me very nervous! Is this made ground in the sense of uncontrolled but broadly speaking fill or we talking old cars and mystery horror?

8m of made ground? yuck, that sounds frankly horrid and would be making me very nervous!

You obviously don’t work in the West Midlands! Regularly see 10, 20, 30m of fill around here.

There is only so much vibro can do and a good vibro contractor will look at logs and if it’s marginal want to see the ground en made in excavation. If it’s particularly variable or loose/soft then piles are usually a better option.

Re: insurance as above, the ground stuff is built on these days if that was a real issue nothing would be built or nothing would be insured.

Provided the foundation solution is appropriately designed for the ground conditions by a compentant engineer then there shouldn’t be an issue as any liability should be carried by the piling contractors PI, and assuming it’s done by a reputable contractor then there shouldn’t be an issue in the first place.

Likely pile depths will be determined by the thickness of made ground and the composition and strength of the underlying natural soils / depth to rock head.

Without reviewing the ground conditions and knowing the required ABP and building it’s impossible to estimate pile length.

At the end of the day you can build on pretty much anything if you spend enough.

30m of fill…….that just makes the geologist hiding deep inside me cry 🙁 I think I was a little spoilt out in Oz, lots and lots of lovely rock! Starting of my career in London based SI, I just associate made ground with contam or unexpected dead people.

Did a few trial pits yesterday to 8 m

….you must have a jolly big digger…..l

Chartered Geotechnical Engineer, consultant and pile designer (Wallap, Plaxis, slope-w etc).

Find a local Civil/Geotechnical Consultant and pay them to analyse this. Sorry but it is a bit of a “how strong is my steel beam” type of question. The answer could be may things.. skin friction, N-values, Pore water pressure, density, soil stiffness (young’s modulus) etc.. piles can be any depth from a few meters to deep offshore mono-piles. Piles can be very complicated to design and install as they can operate in tension, compression and have eccentic loading.

Re: insurance as above, the ground stuff is built on these days if that was a real issue nothing would be built or nothing would be insured.

Subsidence is a standard insured peril in commercial insurance policies, but equally subsidence of made up ground, e.g. former landfill sites, is a standard exclusion in every insurance policy.

I suspect that this is only not a ‘real issue’ most of the time, because businesses don’t realise that their premises are on made up ground and so don’t realise (i.e. insufficient due diligence) that the exclusion will mean that any claim for subsidence may well be declined. Even if they do know it’s made up ground, they would need to appreciate that could affect their cover and they would need to communicate that to their broker and ask for the exclusion to be removed. I don’t think it’s unusual for that not to happen, and I also think that the chances of getting the exclusion removed are slim if the asset value/revenue generation/criticality is high and the pilings do not extend below the depth of the made up ground.

Not 100% sure what original poster is planning on doing but I would contact the likes of Keller, Cementation Skanska, Bauer, Van Elle or Keltbray and check prices for bore piles using a Klem 702 or 709 rig. Blast through that lot quicker than any driven pile rig. You are unlikely to drive much through 8m of made ground.. rotary piles the answer.

I still wanna see the digger that digs the 8m trial pit….. 😀

Coconut + 1

I’d recommend Van Elle and Keller. Also Abbey Pynford and Vibro Menard.

I couldn’t recommend Roger Bullivant or Balfour Beatty.

I still wanna see the digger that digs the 8m trial pit….

Stop being such a smart arse 😆

^^^ 😀

I can’t recommend avoiding Van Elle strongly enough (in particular the drilll and grout division) but I’m not going to say more on an open forum.

Slowster – ain’t no-one going to put there name to a pile bearing in or using skin friction within made ground. If some one builds on a pile bearing in some who-knows-what made ground the. I would suggest that getting insurance is the least of their worries. The whole idea of using piles is to extend through the shite ground to bear within the competent strata below. I.e. Transferring the load to ensure that settmwnt isn’t an issue.

Again anything is possible but without seeing logs and data it’s all guess work.

If you want pointing in the direction of a Geotechnical engineering firm / structural engineers in you neck of the woods then drop me an email.

Also Coconut +1 (apart from the Van Elle bit).

OP, your profile says you are a site engineer so presumably you are in the civil engineering industry and maybe have some contacts in the geotechnical business ? They are the folk to speak to.

Slowster – ain’t no-one going to put there name to a pile bearing in or using skin friction within made ground. If some one builds on a pile bearing in some who-knows-what made ground the. I would suggest that getting insurance is the least of their worries.

A particular case I was involved with probably is probably costing the company millions, but I know that getting insurance was definitely not the least of their worries, since if the movement increases it might cost tens of millions, potentially in the worst case upwards of £100M.

I realise that not getting subsidence insurance for such premises may seem minor, but it is potentially a huge issue, and something which could kill a project dead when a board realises the uninsured financial risk that will hang over the company for most of the projected lifespan.

Slowster you misunderstand; my point was that insurance is a moot point if the building is constructed on a poorly designed pile and no reputable engineer or piling contractor would put its name to a pile that’s designed to bear within made ground.

I can assure you from current experience ground reports, boreholes, dynamic probing and all the jazz you want to chuck at your foundation design may still catch you out and throw up a world of shit. Get driving and wait for the set that’s when you know you may have founded properly.

wait for the set that’s when you know you may have founded properly

I think the point being made is that in made ground (as distinct from engineered fill), you may achieve the set on something unstable. Five or ten years later, the fill has degraded and shifted and the pile capacity is lost.

Wow thanks for all replies..
trial pit driver had to dig a lower platform to reach bottom! sides stayed up on there own quite firm /strong fill looks to have been compacted as laid.
Had possible piling contractor along to assess along with our structural eng. Hippy its in Tipton seems like you know the area there are 4 known mine shafts on site! Im sure all structural aspects and warranties wil be looked at I was after a bit of background on vibro work generally I know it will depend on individual conditions we have had to give up with vibro on leeds site made ground was too loose and column fill migrated sideways but looks like good ground is easily within possible depths possible start in January.

My solution would be: Inject a polyurethene grout to improve the ground strength. There are some excellent products out there, Network Rail and London Underground now glue the ballast on the edges of some embankments using these grouts.The dynamic live load of a train is way way higher than any dead load from a small building. Once you improve the overall granular made ground you build a raft foundation, no piling or significant excavation required. Ideally you would locate the mine shafts with ground penetrating radar, and backfill with 6F2 or 6N engineered fill.

jag61, what will be the general nature of occupation or use of the building?

I see a lot of advice has been given already, some I’d agree with, some I definitely wouldn’t. It doesn’t sound the most straightforward of sites (which ones are now!), but I’d say the most important thing is to get a geotechnical engineer appointed to give you some professional advice following a review of all the info. A few grand in fees will be nothing compared to the costs if it all goes a bit pear shaped. Happy to discuss further and in more detail off-line (consulting engineer here who worked for one of the piling & vibro contractors noted above for a good few years).

Jag61

As you have 4 mine shafts on site then I assume you have underground workings which require D&G treatment as well?

If so most piling contractors won’t put a pile above grouted workings as they will want to extend the pile to below the treated horizon which means exceedingly long and expensive piles.

I’m based in bham and work extensively in the Black Country and with mining issues.

To be honest you’ll probably end up going with vibro but having to go with pre-boring and full thickness treatment.

Again email in profile, I’m on leave this week but can put you I. Touch with someone in the office that can review.

Edit. Also the Mine Shaft treatment advice above about backfilling with granular material is unlikely to be approved by DMBC and you’ll need to drill and grout the shaft in accordance with Ciria SP32 within 10-20m of your development to get the Coal Authority to sign off with DMBC. They usually push for capping however with 8+m of fill you may have to form a grout cap at rock head depending on proximity to the development footprint.

I see a Singletrack Consultancy forming….

£500 + VAT is the going rate I believe 😀

I see a Singletrack Consultancy forming….

£500 + VAT is the going rate I believe

As long as I can work from home I’m in!