"Ground heave precautions"

[eandg]

I'm trying to compare like for like with piling and ground beam quotes and have one (which is overall the best) attributing £2.3k or thereabouts to "ground heave precautions" that aren't detailed further and aren't included in other quotes (or noted by engineer on his drawings). A quick google suggests heave precautions may be required where you are building near trees but I can't find a lot else on it that tells me when and why they may be required. Any thoughts - contractor 'at it'?

[Big Jimbo]

If you are on clay, you will need heave protection under, and the inside wall of your ground beams.

[eandg]

2 minutes ago, Big Jimbo said:

If you are on clay, you will need heave protection under, and the inside wall of your ground beams.

Thanks - we're on made ground which is why we require piles, any thoughts?

[Mr Punter]

Unless the made ground is overlying clay there should not be heave issues.  Ask them why they are included and if not required you could deduct the cost.

[markc]

Piles should go straight through any (shallow) clay layer isolating the structure from heave or shrink

[eandg]

Thanks both - I'm planning on going back with a few bits and bobs for negotiation so shall be asking for those costs to be removed too; benefit of the doubt they've maybe presumed it's in clay given we're going for piling. 

[Timedout]

Whoever it is may want to be assured any volume change in the ground between the bearing point of the piles and the surface will not lift you piles. They may just want a slip plane between the piles sides and the ground to reduce friction. Perhaps a sleeve around the pile.

This is not my line of work but I know this is not a delusion on my behalf.

[ToughButterCup]

As luck would have it,  we are on made ground over glacial till; clay. And we have ground heave precautions .

 

Thats code for a French drain all the way round the house.  Placed about 400mm below the surface, bedded in some stone.  In all about 100 meters.

 

Cost? Can't remember .

But it took half a day (tops) 15 tonnes of stone , 100 meters of pipe, two blokes, ie one person day. £200. Stone £300, pipe £100, machine £200, mark up £100. Say £1000.

Because our site slopes, and the heave protection pipe discharges 10 meters down our garden, I persuaded our BCO to allow us to duct our rainwater from the roof into that piping in order to supply extra water to our attenuation 'bog' (or GCN factory - a shallow marshy bit where theres already a small spring) as part of our ecology and SUDS program. I've been digging that pipe line today (£280 pw for a 3 tonner). Saved spending a cople of thousand on plastic crates and stuff. 

Overall our heave protection paid for itself.

[Gus Potter]

Good points from all.

 

Eandg.. a good place to start is to look at the NHBC guidelines on building near trees. You'll find this online.  Good explanation and diagrams. Type into search engine "NHBC building near trees setion 4.2." This will give you a good start.. easy to read.

 

Clay shrinks and swells and it does this in all directions, up and down and sideways too.

 

Your Engineer seems to be excluding this and passing design responsibility back to the piling contactor who has at least picked up on this.

 

Turning to your quotes.. for a lot of domestic applications ( well commercial too).. some piling contractors work on the premisn of "who dares wins"

 

When you are designing piles you want to make sure that you are not driving though made ground / fill. If this moves it can drag the piles down too so you need to take this into account.

 

Sounds like you don't have made ground so look on the bright side.

 

If you want to post the calculations and results of any gound investigation.

 

 

 

 

 

 

 

 

[eandg]

18 hours ago, ToughButterCup said:

As luck would have it,  we are on made ground over glacial till; clay. And we have ground heave precautions .

 

Thats code for a French drain all the way round the house.  Placed about 400mm below the surface, bedded in some stone.  In all about 100 meters.

 

Cost? Can't remember .

But it took half a day (tops) 15 tonnes of stone , 100 meters of pipe, two blokes, ie one person day. £200. Stone £300, pipe £100, machine £200, mark up £100. Say £1000.

Because our site slopes, and the heave protection pipe discharges 10 meters down our garden, I persuaded our BCO to allow us to duct our rainwater from the roof into that piping in order to supply extra water to our attenuation 'bog' (or GCN factory - a shallow marshy bit where theres already a small spring) as part of our ecology and SUDS program. I've been digging that pipe line today (£280 pw for a 3 tonner). Saved spending a cople of thousand on plastic crates and stuff. 

Overall our heave protection paid for itself.

Thanks for that - if you have any drawings that you could share that'd be great. Given the costings it's something I'd ask the groundworkers to do rather than get done by the piling contractor. 

 

 

 

[ToughButterCup]

Drawings? ?Drawings?

 

I'll dig out some photos: much more use to you. As it happens the ground heave pipe is partially exposed at the moment so I will take some pics and post them. 

 

By the way have you thought about the range of piling systems available? I ask because steel sleeved concrete was too expensive for us. Have a read of this  . Much,  as in very much,  cheaper. 

[joe90]

A bit late to this thread but we are on heavy yellow clay, some trees not too close and no roots in trench,  not made up ground and our BC simply said trench foundations 700mm deep. We did put a French drain around the outside but this was because we have a high water table .