Ground Investigation basement london

[Tony C]

Hi, I am building a house with a one room basement in East London.

My structural engineer is recommending the Ground Investigation to be done (fine), but with 20m bore hole soil test.

Isn't a bit too excessive? I had looked some other people's soil investigation report which has been submitted with the planning application, they contains approx 6-7m bore holes test.

 

Has anyone done basement ? What was the requirement for the soil test from the structural engineer?

And any Ground Investigation company recommendation welcome!

 

 

[Bitpipe]

I've done a 120m2 basement in Berkshire, we're on clay/gravel/chalk. Was a knock down and rebuild 

 

SE recommended 10m dynamic probing (10 locations) and 3x 5m cores  - first pass was inconclusive so we did it again and doubled the number of probes / holes - got more certainty that way. Big concern where we are is chalk solution features (big voids) and made ground. Luckilly we did not encounter either but still needed a big slab (300mm thick, lots of rebar).

 

Quotes for GE varied wildly, the firm I ended up using (recommended by SE) did not have a great engineer on the job initially, they did a better job on the second pass but of course I had to pay twice.

 

20m does sound deep but depends what you're sitting on and what they're worried about (London clay?)

 

I'm a firm believer that you need to know what's down there before a spade goes into the ground as if you discover something unpleasant then it will be more expensive to remedy as you've started the job.

 

What's your proposed excavation & basement build strategy?

 

[Declan52]

20m isn't that deep.  Your basement is going to sit 4m below ground level so a normal 6m borehole won't cut the mustard. 

As you are in East London the  SE is probably worried about London clay so is making sure whatever he designs is fit for purpose. If you want a basement then it has to be designed by a SE then he needs all the info he can get and this means going to 20m. 

[vivienz]

My ground investigation went down to about 7m and that was for a reduced dig of only 800mm.  We had piles put in and these went down to 12m, so 20m from ground level for a basement doesn't seem unreasonable.

[ToughButterCup]

The bottom of our piles are 4 meters down. Our survey went down a little deeper than that.

20 meters in your case seems sensible.

[Tony C]

Thank you for your replies.

At the moment our SE recommending 1 x 20m borehole test and 8 x 1m deep trial pit dug  (to see the neighboring house foundation and our own perimeter wall's foundation ).

 

So far we had 3 company quoted betweek £8-10k......

[Tony C]

I am assuming the Ground investigation is Zero rated (VAT) ??

[Ferdinand]

1 minute ago, Tony C said:

I am assuming the Ground investigation is Zero rated (VAT) ??

Leaving that one for @newhome.

[Mr Punter]

9 minutes ago, Tony C said:

I am assuming the Ground investigation is Zero rated (VAT) ??

 

VAT charged 20% on ours.

[Tony C]

interesting

4 minutes ago, Mr Punter said:

 

VAT charged 20% on ours. 

interesting.

https://www.gov.uk/government/publications/vat-notice-708-buildings-and-construction/vat-notice-708-buildings-and-construction

When you read the following paragraph, it sounds like : when the site investigation is carried out after the planning permission = zero rated.

 

Services in sub-paragraph 3.3.4 are standard-rated where, for example:

• site investigation or demolition work is carried out before planning permission for the construction of a building that qualifies for the zero rate has been granted

[Mr Punter]

I think this is a grey area and just gives an example of when this is standard rated, not when it MAY be zero rated.  For me it makes no difference as we run this as a business and can reclaim the VAT in any case, but we have always been charged VAT for SIs.  I have spoken to HMRC before re: zero or reduced rating and their take is that it is up to the supplier to apply the lowest applicable rate.

[newhome]

Others have certainly been successful in getting site investigation work zero rated as long as it is ‘doing’ work (as opposed to a survey or a desk exercise) and as long as planning permission is already granted for a new build. Definitely worth a punt. 

 

 

[newhome]

Here is an example 

 

https://forum.buildhub.org.uk/topic/6851-a-guide-to-the-vat-reclaim-process/?do=findComment&comment=117279

 

 

[Tony C]

Update:

SE was originally thinking to go for piled foundation (expensive!), then opted for the trench fill foundation.

So the final spec for the SE changed to : 1 x 10m bore hole , and 7 trial pits (examining existing foundations) and associated soil chemical tests and report.

 

We had quotes from SI company which varied 4-7k for this, and in the end I went for someone MikeSharp01 recommended.

Thanks Mike!

[Danny68]

Novice question ? is that just for the test drilling? 

 

[Tony C]

Its for 10m borehole drilling, 7 trial pit digging (currently 4inch concrete surface), and chemical test, and reporting.