UKH

we'll need some form of piling for domestic extension, exact details tbc, but it will likely be beyond scope of regular builders so need a specialist piling contractor. wondering if anyone knows a way to advertise a tender for this, or any general tips. i can obtain multiple quotes and obtain references just from googling companies, but if there's a way of putting it out to tender where lots can see it that would be great.

other tips on procurement welcome!

Won't the architect or engineer that has specified them be able to help?

jk

The only tip I can give is to be prepared for some eye-watering quotes!

Are you using a main contractor - if so, wrap the piling up within their package as a "contractor design package" - risk and price is with them - decent builders will deal with other trades so will know how to deal with a piling contractor

If doing the rest of the build yourself then ask engineer for outline spec, issue it round a few piling contractors (there wont be that many) and get your engineer (or architect) to review it and watch it on site whilst the works are carried out

Get a guarantee / warranty for the works

Assume your house is piled hence the need for piling a domestic extension - query the design of the engineer otherwise

I had to use piling on my own extension because of complications with the run of drains from adjacent properties.  It needed engineering calculations, which the piling contractor sorted out, but wasn't horrifically expensive - worked out about £300 a pile from memory.  It was an interesting day - very noisy work in a blizzard - and worked perfectly in solving the particular challenge we faced.  It would have cost a lot more to dig out a fairly long foundation to the necessary depth to clear the drains (and then time and cost of building up - even the pour volume would have doubled) and the piling allowed us to proceed within a day or two with the drains protected.  I had to install movement joints at the transitions in foundation types, but that was trivial and invisible after the event.  In my experience, the specialist company that I contacted were great and prevented a substantial delay.

Thanks all, some good pointers in there. Architect is a bit useless, engineer can give me a few places to go for quotes but want to make sure I manage the tender process well  

anyone used tender tiger or similar? 

Hi mate, i'm a structural engineer myself and often have to sort out tendering for piling. You're best just doing some research on google of local companies, provide them with a specification of what you want, usually in the form of a drawing with relevant notes and loading and ask for a price. Then you need to carefully read through what they are offering as some will give a quote assuming a certain pile depth and then give a price per additional metre. Others may give a higher quote but allow for a longer pile depth (but may offer a refund on metreage not used). Have you done any investigation into the ground, ie know how deep the piles need to go?

As for advertising to tender, to be honest, i'd be skeptical of companies that are not immediately advertising as piling contractors (i.e. at the top of google). You may get dodgy outfits that are low on work and either will sub contract it out to a dodgy mate with a piling rig, or be that mate himself. You want a proper qualified company doing such vital work, as obviously the repercussions of a bad job can be severe!

Let me know if you haveany questions. Hope thats of some help.

Ta, v helpful. I’d hope that with technical designs specifying depth needed the quotes will be easy enough to compare but yes will look carefully at cost per metre of depth. 

Site investogation (boreholes) booked for next week, so should inform the engineer design nicely. Half the house is on made up ground (Victorian gravel quarry), only concern with the inspection boreholes (10m planned at engineer suggestion) is what if they don’t get deep enough through the made up ground? No idea how deep it could be. Have you ever heard of gravel backfill being deeper than that?

On the tendering, thanks will stick to google results. There seems to be a few massive national companies, will try some local ones too. Is it common for smaller companies to travel far for this do you know? Not sure how saturated the market is really. 

Appreciate ur help!

If it’s a backfilled gravel pit then it seems unlikely it will be > 10 m deep, unless it was a proper quarry that was benched etc. The difference should show in historical maps. 

Assume the drilling contractors have been made aware of the assumed ground conditions so they can use an appropriate method? Could be tricky drilling if there’s all sorts of large material in the backfill. 

I can’t say I’ve ever come across that much fill, no! But I’ve never worked on an old quarry site. If you google bgs and go on the top hit which is the British geological survey site, put in your postcode and it’ll take you to a map of your area. Click on borehole scans and it will show you any local boreholes that have been carried out and registered. It can prove extremely helpful in giving a good idea of depths of strata. Depending on what kind of rig they are using, they should be able to keep going past 10m, there may just be additional charges, but you may as well after going that far. If they have a rig going 10m it won’t be a window sample rig so should be no problem.

If a company is prepared to travel and they’re not offsetting the cost of doing such onto you then great! Get the quotes back and see what you’re dealing with firstly.

Have a look on old-maps.co.uk - you might be able to see the extent of the quarry and get a feel for how deep it was.  I've worked on former quarry sites with made ground down to 15 m but as said by Arms Cliff these are proper quarries. Has a desk study been done prior to the ground investigation? 

As mentioned above a window sample rig might struggle to get down to 10 m in backfill, especially if there's boulders etc where you will just get a refusal.  The drilling contractor should know that so sounds like they might be planning to use to slightly more substantial rig to get down to that depth.