Jump to content

Ground Investigation basement london


Tony C

Recommended Posts

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!

 

 

Link to comment
Share on other sites

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?

 

Link to comment
Share on other sites

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. 

Link to comment
Share on other sites

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......

Link to comment
Share on other sites

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
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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. 

 

 

Link to comment
Share on other sites

  • 2 months later...

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!

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...