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Piling - is testing required?


eandg

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I've a couple of quotes, both of which include fixed charges for 'static load testing', which is more expensive than the piling itself. They also include charges for 'dynamic load testing'. Are these required or advisable?

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Nope, didn’t do mine. 

It would depend on what type of pile, there are many types. 

A driven pile doesn’t get tested as it is driven until it reaches a certain standard. 

@AnonymousBosch used a stone column which is known as ground improvement, so it gets tested to see if it has reached its design capacity, so it’s really down to what you are getting. 

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Piling is  a very interesting topic.

As I (imperfectly) understand  it, piles of many types -  are driven, screwed or compacted to whats known as a Refusal - simply a calculated back- pressure beyond which its not worth doing any more work (called the Working Load I think, maybe wrong). 

Refusal sometimes therefore varies by position. In our case one of the 64  piles just shot into the ground - to Refusal at about four meters. Most refused at a bit over three meters. One hit an incursion of rock. Because it was the last pile driven I could hear the difference in the cadence of compaction. And the ground really shook. The rest sort of slithered in.

 

Just for completeness, @eandg, piling cost us £6500, Groundsure test , about £2500 ish, and one critically important letter (email) from the SE - one that together with a bit of research on my part and help from BH members saved £17000 (yes 17K) . Hillard Tanner saved his fee many times over. Top bloke - and his partner Nick Bailey.

 

Ours were tested to 2.5 times the static load. One or two of the piles achieved 3 times the static load and one a little more.

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Thanks AB - I can't find the quote now (on my laptop which is tucked away for the day but the static load test was something like 4k). Our SE has just come back to say static testing is overkill and dynamic testing of a sample is all that's required - which is a relief. 

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With concrete piles they often do pile integrity tests to make sure there are no defects along the length of the pile.  I think they connect a sensor from a tablet and tap the pile with a mallet.  Somehow this tells them a fair bit.  They do it for every pile.

 

You may also need concrete cube tests.

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ours were odex piles (I think), 220mm diameter and knocked in until hit rock, then a bit more and then a 1.5M drill through bottom.  Steel case is used as the pile, then rebar and grout to top.  42 for our house and was apparently overkill for a single house, but there we go. 25K and 4 weeks work

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  • 6 months later...
On 18/05/2020 at 23:14, redtop said:

ours were odex piles (I think), 220mm diameter and knocked in until hit rock, then a bit more and then a 1.5M drill through bottom.  Steel case is used as the pile, then rebar and grout to top.  42 for our house and was apparently overkill for a single house, but there we go. 25K and 4 weeks work

 

Hi Redtop,

 

Sorry for the questions, but in process of geting quotes for piling and figuring out options..

1. Which companies did you get quotes from? and who di you go for? 

2. How deep did your piles have to go?  Noting £25k for 42 piles.

3. Why did it take 4 weeks?   One company I am getting a quote for 33 piles says 2.5 days. (they do screw piles) Sounds like yours were driven piles....is that the sort of time they take ot drive in and fill...or were there difficult conditions at your site? 

 

Thanks for info!

 

Paul

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2 minutes ago, Paul S said:

 

Hi Redtop,

 

Sorry for the questions, but in process of geting quotes for piling and figuring out options..

1. Which companies did you get quotes from? and who di you go for? 

2. How deep did your piles have to go?  Noting £25k for 42 piles.

3. Why did it take 4 weeks?   One company I am getting a quote for 33 piles says 2.5 days. (they do screw piles) Sounds like yours were driven piles....is that the sort of time they take ot drive in and fill...or were there difficult conditions at your site? 

 

Thanks for info!

 

Paul

 

I hink can answer my last question myself having just looked up ODEX piles...I realise youe site WAS difficult if you have to go into rock!  So doesn't sound comparable to our situation at all!

£25k then looks like a bargain!

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21 hours ago, Paul S said:

 

I hink can answer my last question myself having just looked up ODEX piles...I realise youe site WAS difficult if you have to go into rock!  So doesn't sound comparable to our situation at all!

£25k then looks like a bargain!

Yes site was steep, muddy and hence why it took so long. House not going anywhere though :_) oh and house is lifted of ground on steel stilts, that puts a side load on foundation pile which increased the requirement.. One side of house is 12 inches off the ground. 6m to other side of the house it is 2.5m off the ground. Thats how steep it is

Edited by redtop
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  • 10 months later...
On 01/12/2020 at 12:04, redtop said:

Yes site was steep, muddy and hence why it took so long. House not going anywhere though :_) oh and house is lifted of ground on steel stilts, that puts a side load on foundation pile which increased the requirement.. One side of house is 12 inches off the ground. 6m to other side of the house it is 2.5m off the ground. Thats how steep it is

Sounds awesome- any pics of the house?

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I have an odex job coming up soon.

 

@ £9200 for six piles, I know its definitely not the cheapest method.

 

It is a very effective method though, and on problem ground, solves many problems.

 

What I'd give to be able to bung in a simple strip foundation.

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6 minutes ago, DragsterDriver said:

Piling costs are reasonable but the ground beam costs are insane atm.

 

Well, for my own job, I can get pre welded cages for under £1k  and the concrete isnt much on top at all.

 

The piling cost is a killer though for six piles.

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Great points form all.

 

For all.

 

In the past often we wanted to make sure that a pile could carry the design load. Say you have ten / fifteen piles then the SE / Geotech Engineers may come to site an pick one or two at random for testing. The static load test basically involves bringing a lot of kentlege (heavy weights) to the site and making a cradle spanning over the head of the pile. You then put a big jack between the pile head and cradle and pump it up while measuring how much the pile sinks by and the time it takes to sink by a certain amount. This a bit like the CBR test that you see mentioned for your access  / drive or hard standing... but more complex as the risk is higher.

 

This static testing takes a lot of time to set up hence the cost. You need space and there is a cost to; bring the kentledge to site, build the cradle and make sure folk don't get sqaushed! One other (not least) problem is that you have to calculate the probability that you have not just picked the two best piles!

 

Now with modern calibrated piling rigs and computer analysis the piling contractor can gather a lot of info on say a driven pile capacity as they are knocking it in.  A concrete pile say is a bit like a tuning fork so you can measure the frequency of the vibration as the hammer hits the pile and how much it is driven in by each time this happens. You then compare this with a known data base of responses. You can even let the pile rest for a while and go back and give it another few taps with the piling rig as some piles behave a little differently once the soil / water pore pressures stabalise from the intitial intrusion of the pile. A bit like bread or reheating a curry the next day.. piles can be better or worse after a few days!

 

 

On 18/05/2020 at 17:36, Mr Punter said:

With concrete piles they often do pile integrity tests to make sure there are no defects along the length of the pile.  I think they connect a sensor from a tablet and tap the pile with a mallet.  Somehow this tells them a fair bit.  They do it for every pile.

 

You may also need concrete cube tests.

Good point Mr Punter.

 

Concrete piles can shatter under the ground. They may take a static load test too. One thing about a static load test on a pile that you are going to use is that you often only test it to the working load or a little more. If you test it right up to the point of destruction then you now have a useless pile and that poses a problem. Often a dynamic test will identify piles that have shattered as the frequency response is different (burst tuning fork) still a problem but at least you know and can do something about before you construct a building on top.

 

The ODEX pile is pretty cool but simplistically is a big drill bit with a large say Bocsh type SDS drill on to top but a lot more expensive.. not available at Screwfix. As the hole is drilled it's cased with a steel tube to stop the sides of the drill hole from falling in.

 

In say parts Glasgow (off the top of my head I can't name locations in the rest of the UK.. any input from BH folk welcome) there is a certain type of boulder clay that contains boulders the size of cars / houses. Surrounding these is often a very soft material. In a BH context for low rise domestic housing this is not often a major issue, provided your pile is not scuffing the side of the boulder, load it up and the end will be stressed just like when you break a drill bit hitting a nail in a bit of wood. The ODEX pile concept (not new though! ) is also good for when you have say cavities in the ground like mine workings or a layer of fine sand / silt that washes into the bore.

 

To kind of finish this. You can see on the BH resource that it's really hard to get a handle on the cost of piling. However, hopefully you can see why the cost of dynamic testing is less than the static load test appoach in cases applicable to what we are doing on BH.. much depends on the type of pile you have though. A screw pile is a different animal and needs a different approach for example.

 

Again for all.

 

As a starting out BH member looking at piling. For me the first step is to look at what you need the piles to do. Do you just need them to carry vertical load or do you need them to carry sideways loading too. Sideways loading can occur for example when:

 

1/ Your house is elevated off the ground and thus the piles need to act a bit like a cantilever to resist the wind load.

2/ You have an elevated house due to flood risk.. near a river where you want the flood water to be able to flow under the house. Here you have to take into account scouring of the ground around the pile, getting hit by floating tree trunks etc, the sidways loading of the water on the pile..

3/ You are building on a slope with a soft layer of clay that could slip and impose sideways loading on the piles.

 

If piles need designed for horizontal loading then the cost can jump significantly.

 

For piles that only need to carry vertical load then often much easier on the budget.

 

The key here is to spend money on a good site investigation. For example trial pits, window sampling, shell and auger rig, boring if need be. This gives you the raw data.

 

In terms of reporting there are two "halves" to a soil report. An investigation report.. this has the data that was logged and that is it. The other half is what is called the interpretive report. Here say the Geotech Enginneer will tell you what kind of piles will be suitable, how big / long they may likely need to be, alert you to potential ground contamination and so on. An interpretive report carries a lot more liability so expect to pay a good bit more.

 

On the other hand expect to save money when going to tender. In the round you'll probably come out quids in and you will reduce you financial risk! Just you'll need to stump up early doors... which most folk are reluctant to do as often folk think site investigation is just like council tax.

 

Hope this helps.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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So they are using a mini piling system such as grundomat yes?

 

Driving rather than drilling is considerably cheaper, but even so, your piling costs are low, so well done on that.

 

I had quotes for my job that were cheaper for both piles and beam using driven system that was lower than piling alone when using odex.

 

Its nastily pricey.

Edited by Makeitstop
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6 minutes ago, Makeitstop said:

So they are using a mini piling system such as grundomat yes?

 

Driving rather than drilling is considerably cheaper, but even so, your piling costs are low, so well done on that.

 

I had quotes for my job that were cheaper for both piles and beam using driven system that was lower than piling alone when using odex.

 

Its nastily pricey.


yeah standard driven- the ground is fen peat/clay like a big pudding, it’s horrible!

 

I’m going to price up the rebar to do the beams myself and see what’s what- I know the raw material cost has doubled since I last did some. Probably going to go with raised piles with beams on top which will save £20k when accounting for block and brickwork to dpc. It needs to be well over 1

metre above ground due to being in a flood zone.

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I guess you have soft ground at depth, whereas I have soft / hard / soft / hard / rock, with frequent cobbles and boulder suspected.

 

On your beam costs, for the apparent scale of it, it doesn't look overly horrible, but any saving is worth having isnt it.

 

 

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5 minutes ago, Makeitstop said:

I guess you have soft ground at depth, whereas I have soft / hard / soft / hard / rock, with frequent cobbles and boulder suspected.

 

On your beam costs, for the apparent scale of it, it doesn't look overly horrible, but any saving is worth having isnt it.

 

 


for sure, the ground is horrific. 
 

materials have risen so sharply it’s hard to know when I’m being tight, unrealistic or what :) having done some steelfixing my automatic answer is always sub it out...

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