Piling Foundations

[dsaunders]

Hello, we are currently awaiting our SE to complete design for our rc ground beam and pile layout. I just wanted to write here to get a second opinion hopefully, as currently it looks to be a very expensive option! Ultimately I trust he knows best, after all he is the expert, but considered there was nothing lost putting it here for some thoughts.

 

So we had some trial holes completed, findings were not great, SE came back another time as it was variable between different locations but it was worse second time around. Had to arrange boreholes, one at 10m and one at 20m. Both borehole results were wet, white chalk (recovered as putty chalk). Our builder suggested a raft, and after reading on this forum and seeing they appear very popular, I suggested this to the SE but he advised our ground conditions vary too much for a raft?

 

So now we have seen his assessment and load capacity possibility, the report suggests 16m and 20m piling ( not sure if they go as deep as that, or just his assessment ), which will be a huge increase in our quotes received for 6m. 

 

I appreciate we’re still awaiting his design but any thoughts are welcomed. 
 

 

[Russell griffiths]

Have a look at a system called ground improvement piles. @AnonymousBosch has these beneath a raft, it’s basically stuffing a big metal probe in the ground then as it’s withdrawn slowly tipping in a stone and vibrating it, you basically end up with dozens of stone columns under your raft to improve the ground bearing capacity. 

 

Many on here have piled foundation and its not a deal breaker IF YOU do the research, if you let your SE loose with your cheque book it can get expensive. 

 

I was quoted £5000 by my se just to design the slab. 

 

He soon disappeared and I replaced him with a piling co that had an in house SE that priced all the design in with the job. 

 

I took a drive around locally  and found a good few houses being built and talked about piling with them, from that I had a good idea what would be needed, so I was pre armed with information. 

[ToughButterCup]

As usual @Russell griffiths beats me to it. I'll need to get up earlier to put one over on him. Just waiting for the right ? moment.......

 

And as usual, he's right. Let me explain.

You know how if you ask a random historian to explain (say) why Brissol is so linked to the slave trade, you might well get the response ' Not my specialism' or 'Not my period'.

Same with SEs. They need the work, they've got expensive professional insurance, they have some experience - go for it sunshine!. Need to pay the mortgage. Your SE might well have some cursory experience with piles - just enough to do some sensible - over cautious / slightly well-informed / it'll do  / work to pay for her partner's new toutou / brogues.

 

In brief, get (a)nother opinion(s). Here's why.

Just like you, we had the ground profile done. Just like you dismayed. Just like you inexperienced. Just like you worridtohellabouththecost.

Standing on our newly cleared, levelled off site stands a man who's just stepped out of a spanker of a Merc. Trophy  Dolly Bird in the passenger seat. Lipstick applicator out, mirror adjusted to suit. Blousy smile. (But nice blouse - suitably immodest and straining at the seams)

 

"Yer maaaate, that'll be £22 grand fer piles: ye'll not get away wi' less "

Really? Have you seen our soil profile?

"Wa? Ya paid fer a soil profile. 'Ow mooch?"

About 2 and a half....

"Mert, ah wood a dun it fer tewundred"

Thats interesting. Thank you so much for your time and interest. I really appreciate the way you get straight to the point. Rictus smile. 'Nother glance at trophy bird. Tea and medals. 

 

Cue posts to BH. And a slow realisation that with effort and careful research, we can get a sensible, well thought through idea about how to do the job both well and at a reasonable price. A raft can be built in a very wide range of situations. Do the background reading. Hillard has written a paper about it somewhere. I'll try and dig it out.

In brief: lots of reading, lots of help on BH lead to  Hillard Tanner, and  Town and Country Vibro. Have a look at my (now mostly disused blog on BH)

 

And a piling cost of £6500ish. Hillard Tanner's enagement with our problem and his  depth knowledge saved more than double his fee. (£2 grandish)

 

9 hours ago, dsaunders said:

[...]

the report suggests 16m and 20m piling ( not sure if they go as deep as that, or just his assessment ),

[...]

 

Nobody can tell when  Refusal  (the depth at which there is sufficient resistance in the pile to take the point load plus a safety factor added to the dead load - in our 2.5 times the dead load) will occur.

Thats why I was very impressed with TC Vibro. In addition to the soil profile, we (together) dug a deep pit to feel (grab some soil and mash it into lumps)  the quality of the soil at a series of depths. (I had a digger in those days ... sob.... )  Refusal occured almost exactly where TC Vibro said it would. Between 3 and 4 meters.

 

Ultimately it's all about risk reduction: reducing the risk to your bank balance. All of the above -loads of hard preparation work- saved roughly £17k.

Do the legwork, network, accept no experts answer as definitive - yes even Hillard's.

 

And do come back and test your ideas on BH.