Recommendation for soil survey

[Barny]

Hi. We are having a raft foundation for our timber frame and need to get a soil survey done for the engineer. We had a quote for £3.5k which seems a lot. Can anyone recommend a firm for soil surveys for foundation design? Many thanks

[ToughButterCup]

8 minutes ago, Barny said:

.... We had a quote for £3.5k which seems a lot....

 

That depends on the size of the job ... 

Ours was for .385 of a hectare, 8 cores (and one free one)  the cost is detailed here (£1260).  I no longer have the contact but the company was based in the NE ...

 

[Gone West]

24 minutes ago, Barny said:

We had a quote for £3.5k which seems a lot.

We had an insulated raft foundation and the SE only wanted a soil plasticity test from the centre of the slab area. He told me what was required, I dug a hole, put a soil sample in a plastic bag and took it to the laboratory. £50 for the results, it was thirteen years ago though.

[Barny]

Thanks. I should say we are in Cambridgeshire. The plot is an acre but the actual house area is 200m.

[nod]

Shop around The fees vary wildly 

[Dave Jones]

we paid £1200 for the core drill and test, they went down 5M. Took around 3 hours.

[saveasteading]

+1 @Gone West

 you have an SE What do they want and need.

It seems strange that they "need" a soil survey from you.

 

On most of my projects we dug a hole, either manual or machine, with our SE in attendance if appropriate, or just me reporting.

If they are local and experienced then they should already know what to expect.

If not then why not?

 

If they don't need several boreholes then it would be a waste of money.

 

Let's go back a stage.

 

You are building a raft. Therefore you must already know that the ground requires a raft? How so, without a ground report?

[Gone West]

37 minutes ago, saveasteading said:

You are building a raft. Therefore you must already know that the ground requires a raft? How so, without a ground report?

We built an Isoquick insulated raft thirteen years ago when we started building our PH. The SE was employed by the company installing the raft and didn't attend site. With my lack of experience I thought the raft was massively over engineered but I knew very little about insulated raft foundations.

[saveasteading]

45 minutes ago, Gone West said:

thought the raft was massively over engineered 

If they have a standard design to suit all possibilities, then it would have to be heavily constructed.

Then on a site with perfect conditions it would be overdesigned. 

 

I had a competitor once who overreacted to any site problem. Basically how can we stop this ever happening again?

His solution, not being an Engineer or building expert was to make every building the same, at great expense to themselves or their client ( he was a  good salesman, if good means making sales).

 

My stratagem on the other hand was to design  to suit the site. He probably thought this was perverse.

 

On previous discussions here I have made the case that heavy rafts are used too often. I agree there is a case to be made for increased certainty at a cost.

I try to avoid saying to anybody you have made a bad choice and have wasted lots of money. 

 

BUT to choose a raft and much later insist on a soil survey seems perverse.

What can they do with any very good or very bad results?

[Gone West]

1 hour ago, saveasteading said:

BUT to choose a raft and much later insist on a soil survey seems perverse.

I may have misunderstood, but you seem to be saying you should only use a raft if it is required by the ground conditions. I chose an insulated raft because it was the best fit for my design of PH. Whether it was over-engineered for my ground conditions I do not know, as I am not a SE.

[saveasteading]

The term raft is used many ways ( discussed a few weeks ago)  so I'm avoiding being particular.

 

To me it is  a very heavy structure. To some it is just a slab. 

 

But I am saying that ground reports should be done before designing or deciding on the method of structure.

 

The only reason for a late survey is probably for ticking a box.....survey done, ground not too bad.

 

Hence it may not need to be an extensive or expensive survey....and the SE should advise and be considerate on this.

 

BUT what about these extreme examples....it us found to be an old peat bog or landfill with minimal strength....OR  it  is solid stone.

What happens? 

[Post and beam]

On 01/07/2023 at 09:21, Barny said:

Thanks. I should say we are in Cambridgeshire. The plot is an acre but the actual house area is 200m.

Try Heriditas in Letchworth

[Barny]

Thanks for all the comments.

we wanted MBC to do the foundations and frame to reduce the risk and MBC only do raft foundations hence why we were going that way. They use an engineer in Ireland hence they don’t organise their own soil investigations.

 

I am worried that a raft is not the right option from a structural (and cost) point of view and this remote engineering approach might miss issues. The site has 2 large poplar trees. Having read the NHBC foundation guidance I am not sure we can use a raft anyway (or it will be so deep it will cost a fortune).
 

Any anyone built near large trees (about 10m away from trees 15-20m high)? What foundation type did you use and who designed them? Has anyone used MBC for foundations on a site that has trees?

 

thanks

[Redoctober]

1 hour ago, Barny said:

Thanks for all the comments.

Any anyone built near large trees (about 10m away from trees 15-20m high)? What foundation type did you use and who designed them? Has anyone used MBC for foundations on a site that has trees?

 

thanks

 

Hello @Barny Not sure this will assist but in answer to your question - we built on a plot which houses an Oak tree in the corner - We had to ensure our build didn't encroach in the area of the tree - namely 10 mteres away. The corner of our house is 12 metres away so all good in that respect. Our foundations were trench type and nothing out of the ordinary

[saveasteading]

10m isn't enough for an oak tree unless the foundations are deeper than standard,  which presumably they were.

 

 

I've answered the original question, as have others, but you are still asking.

 

My opinion on this raft solution appears to annoy some people on here. Nobody wants to think their project is overdesigned.

What I have learnt though is that the mbc package is exactly that, and the raft is part of the deal.

Therefore it should be complete, not leaving ground reports and tree information to the customer.

 

So I will only say, don't dabble. Mbc have an SE who is responsible. So tell them about the trees.

If they won't answer then that flags a responsibility issue.

 

 

 

[Barny]

Thanks saveasteady. That is what I thought too. I assumed MBC would organise everything they needed for their SE but they don’t. It just makes me worry I am exchanging one risk for another.

[Redoctober]

1 hour ago, saveasteading said:

10m isn't enough for an oak tree unless the foundations are deeper than standard,  which presumably they were.

 

😲 just checked my soild survey and attached guidance - ours were dug to a depth of 1150mm - Whether that is right or wrong, our house is still upright. 🤣

[saveasteading]

That's fine if your soil is low shrinkability.

 

If it is clay, then there is an issue.....to be resolved by your professionals. 

[saveasteading]

41 minutes ago, Barny said:

I assumed MBC would organise everything 

It is important that someone has responsibility for the design. 

 

You think it is mbc, but they haven't seen the ground or thd trees. 

Hence, perhaps, they rely on rafts.

 

I suggest you read your proposed contract to see what the responsibilities and liabilities are.

There are several loyal mbc blinds on here, so perhaps they can help.

 

I can't really say any more than I have.

[JOE187]

Could you post a site plan showing tree position and actual height, may be just one corner needs deeper footing!!

[Gus Potter]

On 01/07/2023 at 08:46, Barny said:

Hi. We are having a raft foundation for our timber frame and need to get a soil survey done for the engineer. We had a quote for £3.5k which seems a lot. Can anyone recommend a firm for soil surveys for foundation design? Many thanks

Loads of folk have made some good points.

 

Here is a thing. There are two kinds of soil investigation.. a factual one and an interpretive one.

 

The factual one just gives the results of the investigation. I get these and it is then up to me to work out what loads I can put on the ground where. In this case I carry the can if it goes wrong.. obviously I want to avoid things going wrong.

 

The interpretive investigation passes the liability to the Geotechnical / Soil Survey Company. Here I get a report that says things like..

 

Bearing capacity of the soil is 100 kN/m^2.

 

Plasticity is this / swell shrinkage is this and recommended foundation depth is this... taking into account environmental things like trees ect.

 

Soil is "acidic" in nature thus recommended concrete grade is this. For all.. some soils can be contaminated some acidic and aggresive to concrete so you need to select your concrete grade based on this information.

 

Ground water was found here but could vary by x.. very imprortant as you don't want you raft floating.

 

Now a lot of these companies I deal with are very helpful and give you a heads up if you pay for the more expensive interpretive report. They tell you things over the phone like.. we have worked locally so here is what to also watch out for and here is what you can disregard.

 

But to sumarise. Before I commision a soil investigation I do a desk top study just to get an idea of what kind of founds may work. No point in going for a raft on rock / good chalk. There are load of more efficient ways to skin the cat.

 

6 hours ago, Barny said:

Thanks saveasteady. That is what I thought too. I assumed MBC would organise everything they needed for their SE but they don’t. It just makes me worry I am exchanging one risk for another.

Yes basically you are.

 

In terms of working with a remote Engineer. Yes it can be done. I do some jobs this way where I never go to site. BUT.. this only works if the Client fully engages and spends time learning about their site, the ground and how their self build / extension is going to work. In other words the Client puts in a good effort and becomes a fully invested part of the nitty gritty design team.. imagine yourself as a young graduate .. you are not daft but you don't know very much but are happy to learn.. and once you have learnt you get to make the important design decisions in terms of say structure .. how the drains work and so on.

 

This will take time but if you adopt this approach you will gain a huge amount of confidence. You'll also know that later in the project.. say if you go on more on your own then you can always call up the professionals that helped you at the start if you get stuck. They say that site investigation should take up about 3 -5% of the budget by the way. A lot of professionals have a wide range of knowledge. Architect's know about structures, SE's and Qs's about design.. some good builders fall into the same category.

 

In the round though if you spend the time to learn it can take you away from the day job that often pays the bills. The upside is that you reduce your risk and the process can be very rewarding personally... and that is hard to put a value on.

 

@Barny

 

Keep us posted.

 

 

[saveasteading]

6 hours ago, saveasteading said:

several loyal mbc blinds on here, so perhaps they can help.

that should say mbc clients. 

 

My big clumsy fingers on a small phone. sorry.

[Gus Potter]

21 minutes ago, saveasteading said:

that should say mbc clients. 

 

My big clumsy fingers on a small phone. sorry.

Ah what's the saying..

 

You can take the Engineer out of the Contractor .. but once a Contractor you can't take it out the Engineer.

 

I think you just need to live with the fingers and that contracting is in your DNA..