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Does anyone have a potter's wheel?

vivienz

Entry posted by vivienz

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....because we have clay, and lots of it.

 

A soil test was carried out on the site today as MBC need to know what they're building on to do their sums for the foundation.  I used a firm called Mini Soil Surveys (South West), run by a chap called Martin Shirley.  My selection of which firm to use was detailed and exacting - they were the cheapest.  Or should I say, least expensive.  Actually, I had no idea what was involved in this other than punching a few holes in the ground and looking at which flavour of mud comes out of it.  That's broadly it, but in a much more sophisticated manner and it took a fair amount of time, too, starting at 9.30 and finishing some time around 2.30 in the afternoon, which was much longer than I anticipated.  I rang 4 different companies, both in Dorset and a little further afield, with prices ranging from about £1,400 (inc VAT) up to about £3,000.

 

A mini drilling rig (my terminology is probably entirely wrong here, so please excuse my ignorance) gets trundled onto the site and 3 locations, roughly triangulated on the extreme points of where the new build will be, are chosen.  At each site, 3 sample cores at increasing depths are taken and then bagged up for lab tests, if thought necessary.  Unfortunately, mine are due to a lot of clay coming out in the samples.  The main reason for the lab analyses is to find out whether the clay/soil is shrinkable because this could have a major effect on what gets built on it.  It will take about 10 days for the lab tests and report to be done, so I just need to wait this out and then let MBC know the results.

 

It's not essential for the client to be there, but Martin was keen for me to attend if possible as, in his experience, other things often come to light that may be relevant to other plans for a site apart from the main build.  Although it was a little repetitive towards the end, I did find it interesting and it brought up another job that is time critical and needs to be dealt with sooner rather than later.  The urgent task is to deal with a large amount of hedgerow that runs around the existing bungalow and to do it before it all gets going and growing in the spring.  I had already planned to get the majority of this chopped down (hopefully next weekend) before birds start nesting, but I need to get another long row, an inner hedge between the bungalow and the hedge that separates the site from the lane, as this can have a significant and negative affect on the clay soil there.  It seems that the water demand of hawthorn hedges is enormous and especially so in spring when they get going after their winter dormancy, and by virtue of absorbing so much water from the soil, it causes the clay to shrink massively and the whole lot becomes difficult to build on.  Having to put in piles is a possibility.  Once the diggers are on site, I can get all the roots grubbed out then.

 

The arboricultural report that was done for our planning submission had recommended retaining the inner hedge to act as sacrificial root protection for the outer hedge during construction, but it looks like it will instead need to go and I'll have to get some other sort of root protection in place to satisfy the PP requirements, but I don't think this is particularly tricky to deal with and it's a better course of action than leaving it and having to put piles in.

 

The final point that came up was something that has no bearing on the house, but possibly could on my sewage plant and rainwater reservoir.  Between 2m and 3m depth, the sample had lots of sparkly crystals in it which are some form of sulphate crystals.  Very pretty and all that, but it seems that these, when water gets to them, can attack and weaken concrete.  Both the sewage plant and rainwater reservoir will be anchored into the ground with concrete at just about that depth so I need to make sure that I specify sulphate resistant concrete to make sure that the tanks stay where they are put for the long term.  It's a simple and insignificant difference in cost on the concrete spec, but one that I wouldn't have known to do without the survey.

 

Another day, another load of new stuff learned.

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Gone West

I can't believe the costs quoted for borehole soil tests. I had a 47m deep borehole drilled and sleeved for £3000, and my soil test, which was for plasticity, cost £50.

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Jeremy Harris

@PeterStarck, It seems to vary a lot from region to region, I think.  I can't remember how many companies we approached to drill our borehole, but it was at least four or five, and the variations in price were pretty wide, from around £8k up to over £12k, IIRC, for a ~50m deep borehole.  I already had a hydrogeological report, with a detailed specification for the borehole, including the depth, type of strata to be drilled through,plus details of the type of lining and packing media needed around the water-bearing section.  £3k would barely cover the rig mobilisation costs, here, I think!

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Mr Punter

Trees such as hawthorn and willow together with clay soil means that trench fill foundations may not be feasible even if the trees are a fair distance away.  You may be OK with the passive slab approach but I have never had one designed.  I am interested to see how you get on.  The project we are just completing - silt under made ground next to a river - needed piles to a depth of 25m.  Mucho costo.

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Declan52

The mobilisation cost is always the big one. You are just paying to get the rig there on site. For the type of rig above it was probably a dando terrier which fits nicely in a long wheel 6.5t van. Drove one all over Ireland for a few years. When you go into the holes over 30m then your into much bigger rigs that will need a big compressor as well. So your paying usually for a lorry and a Jeep. 

As for the soil testing very few companies will do the actual soil tests them selves as the equipment is very expensive. Queens university done most of ours or a company in Dublin if it was contamination.

I think @PeterStarck robbed who ever he got in. £3k for 47m is cheap very cheap. Well done!!!

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Jeremy Harris
53 minutes ago, Declan52 said:

The mobilisation cost is always the big one. You are just paying to get the rig there on site. For the type of rig above it was probably a dando terrier which fits nicely in a long wheel 6.5t van. Drove one all over Ireland for a few years. When you go into the holes over 30m then your into much bigger rigs that will need a big compressor as well. So your paying usually for a lorry and a Jeep. 

As for the soil testing very few companies will do the actual soil tests them selves as the equipment is very expensive. Queens university done most of ours or a company in Dublin if it was contamination.

I think @PeterStarck robbed who ever he got in. £3k for 47m is cheap very cheap. Well done!!!

 

Our rig came on a big low loader, as it was a fair few tonnes of kit, plus a landrover towing a big compressor.  IIRC the rig transport was a specialist heavy plant  transporter, with the tracked rig being able to unload itself a bit like a pretty big (15 tonne or so) tracked digger.

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Gone West

I didn't know anything about borehole drilling before we had ours done. This is the kit they used, IIRC it was a 150mm hole with 110mm sleeving. It was eight years ago, so might affect the price. It was the drillers who told me about the wonders of Bentonite which I have since used around my sewage treatment plant pipes. Sorry, a bit off thread.

 

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Declan52

That's a shell and auger drilling rig. To get to 47m with one of them rigs is good going. The deepest you would get here would be not much more than 35m before you would hit rock or mud stone.

It's about as basic as you can get. Lift a big weight with a cutter attached and drop it from height. Clear the cutter out and repeat while getting the casing to go deeper and deeper by either lifting it and dropping it or tapping it with the cutter. 

Bentonite is some stuff. You can get it in pellet form or powered depending on what you want to do.

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Declan52

On a warm day the compressor goes as far away as it can, on a cold day as close as it can. They give of some heat.

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Jeremy Harris
4 minutes ago, Declan52 said:

On a warm day the compressor goes as far away as it can, on a cold day as close as it can. They give of some heat.

 

That it does, and a lot of noise!  Mind you, when  that Casagrande rig was running at full tilt through hard rock it made enough noise to make even the compressor seem quiet!

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SteamyTea

Well the big rig is in place now.

It is bigger than the palms, the obelisk and St Mick's Mound, from the right angle.

Drilling 1.jpg

Drilling 2.jpg

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vivienz

Now, now, boys, let's not have a public rig-waving contest.  Steamy Tea's is the biggest by a long......erm......chalk.

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SteamyTea
31 minutes ago, vivienz said:

chalk

My end is as hard as granite

Edited by SteamyTea
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