Boggy Marshy Drainage

Cmar-Ireland

Hi all,

I am looking at sites at the moment for our self build. A friend of mine has quite a few acres of land and has offered me a choice of areas for a site.
There is one area, 3/4 to 1 acre, that is elevated from the road and is nice and rural, and it looks like the one we will go for (maybe have possibility of a barn conversion too!!!)
But another area of intrest is a boggy / marshy area. I reckon I could get a sizeable chunk of this reasonably priced. The question is, how economic is it to get the area drained. The next field to this is not damp at all, so I imagine if the area was drained or filled it could have site potential.
For a 2800sqft 1.5 storey house would a raft/pile foundation be feasible?
Probably will go for a TF house with hallmark exterior skin.

any opinions or advice appreciated....

cheers

conleth

Hi, when you say marshy ground do you know if it is peat or simply low lying ground with bad drainage?

If it is peat of any significant thickness, be careful as peat can cause all sorts of problems, often at a later date. By profession I'm a geotechnical engineer and have been involved in 2 jobs where buildings constructed on peat have gone bad - one on a raft, the other on piles - in both cases the building has been severely structurally compromised with messy legal battles. There tends to be more problems where there are neighbouring structures (such as a housing development) as your construction sequence can alter the ground conditions in a neighbouring building (and vice versa). Although it depends on the nature and depth of the peat, piled foundations are generally the safest bet (although expensive) but you may find that your services (e.g. water supply, sewer etc.) and driveway starts to settle if they are not also piled. You could drain the peat, but you still don't have a very good foundation soil. Be careful when filling over peat as the settlements are likely to continue over a period of time.

So be cautious!

Conleth

Cmar-Ireland

Thanks for the reply Conleth, very informative.
I don't know if it is wet land or peat. There is no other houses within a couple of hundred meters all round.
I dont know if it would help, but I have an ariel photo of the area, I'll post it when I get home.
Is there a limit as to how thick the peat could be before it is unsuitable for draining etc?

conleth

There are no easy answers to these questions and you would really need to take professional advice and have the site investigated properly before making any decisions. However...

If it actual peat and not just poorly drained low lying land, draining the peat probably won't be enough to elliminate the possibility of settlement and damage to the house. You could have the peat excavated and replaced with good quality fill but the economic feasibility of this depends on the depth of the peat. The depth limit for a tracked excavator is in and around 4 m (depends on the size of the machine). If the peat is deeper than this it may be more economical to pile.

Conleth

Cmar-Ireland

This is the boggy area. You can see the quadrant shape of the area. The grey line in the road and the feilds around it look pretty good.
I don't know if this helps any?
You can see a drainage trench on the lower part of the quadrant, which continues across the field to the right (I was told that the right field drains into this)
The land is approx 1-1.5m below the road level.

conleth

The surrounding fields do look quite good so chances are that your site is just poorly drained - a quick way of determining soft ground depths is by probing. You could use lengths of rebar or something like that - if you can push it through by hand then it is more than likely peat.

Conleth

muffler

I would suggest digging a few test /inspection holes with a JCB but you will need an engineer there to assist with an evaluation. If necessary he can have samples taken and analysed to test compression strength etc.

GreeBo

you'll need percolation tests before you get planning anyways, might aswell do them now (as above)

Cmar-Ireland

What would the approximate cost of getting an engineer in to evaluate the potential site?
The thing is that this is just another option for a site. There are other sites on good land that are available to us, so if testing this area is expensive I might not bother.

conleth

An engineer could go in and do a walk over survey which probably won't tell you all that much without a trial pit (as muffler suggests) or probing. So that's where the costs start to mount up. Most of the work that we undertake is on a much larger scale, but I would imagine a lower bound of a few hundred Euro for a walkover and engineers report up to 2-3 thousand Euro for a site investigation with trial pits, probing and lab tests.

Had you considered asking for permission to go in there yourself and see what you can make of the site? Take a long length of rebar and probe at a few different locations - if you hit anything reasonably solid at shallow depths you have your answer.

Conleth

Cmar-Ireland

I don't think there would be any problem getting permission to probe the ground myself. What do you consider shallow depth?

re the site investigation, do the engineers do all the work? Do they bring their own equipment to dig down etc?

conleth

Well if the soft ground was no more than 1 - 1.5 m deep it probably wouldn't be too expensive to dig it out and replace it with granular fill. If it is beyond 4-5 m deep it would be expensive and at the limit of what most tracked excavators can reach to.

Regarding the engineers, it depends on the type of engineer you would approach - a site investigation company e.g. IGSL, Geotech, Irish Drilling would handle everything themselves but may not be interested in a small job or charge way too much. A consultancy would sub contract the trial pits to a local bloke with a JCB and supervise and log the pit.

You will also get engineers who will give you a good price but not have the faintest idea what they are talking about - you should be employing a ground investigation contractor or a geotechnical engineer. But because it isn't exactly cheap, I wouldn't employ anybody until I could find out as much info about the site as possible - this is where your probing comes in - bring a spade too and start your own trial pit. As I say if you bottom out within a metre you have your answer ad you probably won't need to get in the specialists. Whereas if your rebar starts free-falling through the ground, that site is going to be a problem and you may prefer to walk away without being out of pocket.

Conleth

Cmar-Ireland

Great advice Conleth, thank you very much!

I will discuss with the owner about doing a bit of investigating myself. Hopefully if I can find something solid within 1 - 1.5m.
Now where can I get a 3m rebar?

conleth

Cmar, Curious to hear how you got on?

Cmar-Ireland

Hi Conleth,

I didn't get out to the land last week, but I should be out there this weekend. So hopefully I will have a better idea of the conditions.
Having thought about the work involved in preparing the site, I am leaning more towards the other land. It wouldn't require as much investigation or preparation.

Ciaran

paulocon

Hi all,

Have been tracking this thread (and others on self-build) with interest and would love to hear how things are progressing..

I have just put together my own self-build forum which you can visit at www.selfbuildinireland.com/forum - It's brand new so nothing of note on there yet and I'd really appreciate your support!! Any recommendations, please let me know!

Cmar-Ireland

To update this thread. We are not going to go any further with this for reasons other than the land condition. So we're back looking again :rolleyes:

paulocon

Cmar,

Sorry to hear that.. 'tis a frustrating experience alright.
Best of luck with your search for a suitable site!!