ground investigation

[Hecateh]

So my architect says we need ground investigation for my building plot.  I understand the need for this and it also states in the warranty, (which I have to get for the mortgage).  The warranty wording is 

• Site/Ground Investigation report and any relevant reports identified from this i.e. Tree survey.   

My architect is saying "We suggest four BH’s down to say, 4 metres as a maximum, with SPT’s at 1200 intervals. There are some trees and certainly larger shrubs in the vicinity of the plot and we’re expecting clay-based soils, so please allow for lab. testing – say, up to six sets of MCs / Atterbergs, plus a couple of root ID’s as well please.."  So SPTs I understand are to do with resistance to penetration.  What she hasn't said is that although the soil is clay based we are likely to hit sandstone less than half a metre down.  

 

My groundworker says "The best i can offer you at this point is a excavator which would create test holes where necessary to the depth of 3.3 metres. Let me know your thoughts on this."

 

This is cheaper, though doesn't include analysis of any tree roots.  There is a well established beech hedge a metre away and a couple of huge ash trees a couple of metres away.

 

My research shows that, though there may be ash roots they will be shallow and won't cause any problem - neither will the beech hedge.  

 

Any thoughts, opinions and suggestions welcome.  

[Declan52]

I used to do these. An spt is a test you perform on the ground that will give you a set of results that will give you the bearing capacity of the ground. It's nothing fancy at all, a length of steel rod with a point gets banged into the ground by an spt hammer( a big heavy weight) and the amount of blows it takes to drive down 150mm 300mm 450mm are counted. The likes of peat take 1-2 blows to go the full distance and boulder clay might take 50+. 

If you reckon you will hit sandstone at 500mm get the spade out and dig a few small holes to prove this. If it's there it would be a complete waste of time getting a drilling crew out as each borehole has to be dug to 1200mm depth by hand incase there are any services there that could be hit.

The atterberg test is to determine how the soil will react if it dries out or gets very wet i.e how much it will shrink or expand.

If you can prove that sandstone is that shallow then you won't need a site investigation.

[PeterW]

Hi

 

Have you got a site plan that shows the footprint of the house and the trees..??

 

Ash in Clay is not a good mix - I would be taking them out ...

[MikeSharp01]

A proper cored / bored soil survey, with lab testing and report, should cost around £1500 (Ours was £1100 in Kent with two 6m bore holes, no significant trees within 30m) and give you all the details provided you specify it correctly - I guess your Architect has done this as above. Just digging won't enable the soil samples and won't give you a report, and associated indemnities, you can rely on if something goes wrong.

[Hecateh]

26 minutes ago, Declan52 said:

I used to do these. An spt is a test you perform on the ground that will give you a set of results that will give you the bearing capacity of the ground. It's nothing fancy at all, a length of steel rod with a point gets banged into the ground by an spt hammer( a big heavy weight) and the amount of blows it takes to drive down 150mm 300mm 450mm are counted. The likes of peat take 1-2 blows to go the full distance and boulder clay might take 50+. 

If you reckon you will hit sandstone at 500mm get the spade out and dig a few small holes to prove this. If it's there it would be a complete waste of time getting a drilling crew out as each borehole has to be dug to 1200mm depth by hand incase there are any services there that could be hit.

The atterberg test is to determine how the soil will react if it dries out or gets very wet i.e how much it will shrink or expand.

If you can prove that sandstone is that shallow then you won't need a site investigation.

This is my thinking - except it isn't something I have any experience in so am not able to put forward a valid argument.  I think a big issue is my architect.  She shows no sign of understanding the issue just repeating what what she has said previously.  Maybe she does understand but just isn't communicating BUT it I have less and less confidence in her as time goes on.  I know some things have to be done not because they are needed but just to tick boxes 

 

[Hecateh]

29 minutes ago, PeterW said:

Hi

 

Have you got a site plan that shows the footprint of the house and the trees..??

 

Ash in Clay is not a good mix - I would be taking them out ...

I wish I could.  I am sure they grew as weeds initially as I am forever removing small ones from my garden - and they grow so uickly.  However they are not in my garden and have TOPs.  

[Hecateh]

30 minutes ago, MikeSharp01 said:

A proper cored / bored soil survey, with lab testing and report, should cost around £1500 (Ours was £1100 in Kent with two 6m bore holes, no significant trees within 30m) and give you all the details provided you specify it correctly - I guess your Architect has done this as above. Just digging won't enable the soil samples and won't give you a report, and associated indemnities, you can rely on if something goes wrong.

 

This is the issue.  My architect got me one quote and one quote only for over 2k and with a 3 week lead time.  I have got other quotes and arranged one for £600 it's just that the guy who is doing the ground work is very experienced and says it is not necessary because of the sandstone at a shallow depth.  

[Hecateh]

It seems like I am going to have to go with it just to tick the box to get the useless warranty - to get the bridging mortgage

 

 

[Declan52]

5 minutes ago, Hecateh said:

This is my thinking - except it isn't something I have any experience in so am not able to put forward a valid argument.  I think a big issue is my architect.  She shows no sign of understanding the issue just repeating what what she has said previously.  Maybe she does understand but just isn't communicating BUT it I have less and less confidence in her as time goes on.  I know some things have to be done not because they are needed but just to tick boxes 

 

Your valid argument is that you have dug to a depth of 500mm+ at 4/5 different locations across the site and found sandstone at this depth. Unless you are going to attack this with either a 20t plus digger or a fairly powerful drilling rig  you won't get anywhere near 4m. Maybe she would be happy sending samples of the sandstone away to be tested.

  Either get the spade out or get the groundwork guy to go at it with a digger. Either way will be much cheaper.

[PeterW]

18 minutes ago, Hecateh said:

I wish I could.  I am sure they grew as weeds initially as I am forever removing small ones from my garden - and they grow so uickly.  However they are not in my garden and have TOPs.  

 

Ok - if you are working near trees with a TPO then you need a decent tree survey that will keep the council arboriculture manager happy ...

 

Have you got any planning restrictions on the trees ..??

[Hecateh]

Acronym overload - yes TPO not TOP

There was no reference to the trees in my planning conditions.  They are about 25 metres from my boundary but very tall

 

[PeterW]

Aaaahhhh ..!!! 

 

25m is miles away in tree terms unless the branches come over your plot ..?!

 

Only issue will be the hedge but unless it has any trunks above 75mm diameter at 1.5m above ground it’s not classed as a tree so just crack on ....

[ToughButterCup]

@Hecateh, it's the testing of the samples which is important. If you know exactly what the constitution of the ground is, then a foundation plan can be written on the basis of evidence.

 

We have some sandstone under our clay, some of it is flaky, but one bit of it stopped the piling machine in its tracks (the very last pile). I can go and dig you some sandstone from our site now and you could rub it in your hands and soon there'd be a pile of sand. Other bits of it would take a sledgehammer blow with ease. Across our field , there's an old sandstone quarry - beautiful hard stuff. A test rig tells you exactly what the score is.

 

Grit your teeth and do it right

[Hecateh]

19 minutes ago, recoveringacademic said:

Grit your teeth and do it right

Yep - I'm not unhappy about doing that - I just get scared when everyone I speak to - who is supposed to have knowledge gives me different answers. Add to that an increasing lack of confidence in my architect.  (Her instructions to building control said 'no new sewer or water connection' for example)

 

I am going to get the testing done but I also think I am going to look into finishing my connection with the architect.

 

[Hecateh]

The plot is in the garden of my bungalow, the red roofed one in the picture.  You can see the trees to the south west of the site

 

 

Edited November 15, 2017 by Hecateh
personal info on photo

[Declan52]

Make sure you let the drilling company know that you are likely to hit sandstone at a shallow depth. Depending on how strong it is you might not get a sample using a hollow spt split cone.

[Ferdinand]

@Hecateh

 

Consider the opportunity to make sure your design allows room for a suitable access cul de sac that will not disturb the new or old bungalow, so that you can give access to the next 2 or 3 gardens at some point in the future. ANd the ones that face you back to back.

 

An access route for 3 similar bungalows may be worth nearly as much as your whole plot with pp.

 

It needs to be able to cater for access by fire engines and potentially dust carts etc.

 

That town centre location looks to me to have potential for backlands development at some stage. 

Edited November 15, 2017 by Ferdinand

[Hecateh]

9 hours ago, Declan52 said:

Make sure you let the drilling company know that you are likely to hit sandstone at a shallow depth. Depending on how strong it is you might not get a sample using a hollow spt split cone.

 

Thanks

Yes I've done that.  In fact, they went to the trouble of doing a quick desktop survey before quoting so they brought the topic up.  They said the requirement was probably unnecessary and that it was mainly about box ticking.  

[Hecateh]

9 hours ago, Ferdinand said:

 

 

9 hours ago, Ferdinand said:

@Hecateh

 

Consider the opportunity to make sure your design allows room for a suitable access cul de sac that will not disturb the new or old bungalow, so that you can give access to the next 2 or 3 gardens at some point in the future. ANd the ones that face you back to back.

 

Looking at my photo to discover how you knew it was a Town centre location made me realise how much info I had left on there.  Not that I think identity theft is likely on here but postcode, email etc on internet - not really a good idea lol. I have now edited the photo.  

Did you decide it was town centre just because of the photo or did you look up the location.  

 

As far as access is concerned - sounds great in principle and there could just about be room to put one in BUT I only just got this one passed as Barnsley (currently) won't approve tandem developments and a local councillor was trying to object on those grounds as the current bungalow has a garage (which will become just a store) under the lounge.  The ground slopes a lot more than can be seen from the photo.  

 

Garden grabbing from all gardens without my new build would certainly have had scope for half a dozen houses with modern sized gardens.  

 

The main reason I want to stay in that location.  Small town centre to the North and views to the South,  New propety wont' have quite the same views as will lose depth but still amazing

 

Edited November 15, 2017 by Hecateh

[Ferdinand]

@Hecateh

 

I put the postcode into Google.

 

The thing about preserving the *opportunity* for further access to potential plots is to keep options open, which is often easy, and that it actually uses far less space than most people imagine - I have a modern (less than 20 yeas old) development nearby where the access cul de sac is less than 5m wide for about 5 houses. If allowed, I think the minimum width for emergency services access is around 3.5m at a narrow point for up to 5 houses (varies by County Authority - it is I think a building regs matter not planning).

 

Looking briefly at your PP before I forget where it is I think you have room for such an access through the new front parking space, but I would take perhaps 1-1.2m extra off the back garden of the existing house in that corridor when you sell it compared to the plans just to be sure. Boundaries are not a Material Planning Consideration, so the Planning Authority are very unlikely to do a thing about it and once in place it will not be expedient to do so. You will lose nothing, and will have kept the option open for the future. IMO in 15 or 25 years that site (ie next doors' gardens) will be crying out for a small retirement development of 3 or 4 bungalows walkable to town.

 

Personally I think that - given the lack of housing land and ageing population we have - access to future potential plots inside community boundaries should be a material planning consideration, but currently it is not the case.

 

Ferdinand

 

 

 

Edited November 16, 2017 by Ferdinand

[Hecateh]

@Ferdinand

Thanks for that thought 

 

A combination of moving the house forward half a metre or so and pushing the boundary should achieve that - and like you say, nothing to lose.

 

Will let you know if I manage it.  Hopefully ground clearance starts beginning of December - 

 

Edited November 17, 2017 by Hecateh