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AnonymousBosch

Help me with my little penetrations, please.

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Foundations going in next week, weather permitting. 

What concerns me now is all the things that go through the foundations : foul drain, water, electricity and rainwater recycling - and in our case MVHR.

 

How accurate do we need to be in determining the place that these services come through?

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Here was my list:

 

Two foul drains into the house.

Water in

Water out to outside tap

Electricity in

Electricity out to shed and treatment plant

Telephone

Data cable (spare phone cable)

Hockey stick duct for gas pipe to kitchen island

Hockey stick duct for tv aerial cables etc to under stairs "A/V hub" cupboard

 

The only ones that had to be super accurate where the drains.

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Have you a plan of what's coming through and where? 

Ground floor WC off a rising stack or straight into the floor? That one needs some real thought if the latter.  

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The tolerance I gave to my ground works guy was +50mm, -20mm on the absolute positions of the ducts and pipes coming up through where the slab was going.  He thought I was barking mad, but I really should have tightened this tolerance up a bit, as the soil pipe ended up about 10mm too close to the wall.  All our pipe and duct positions had to be fixed with the Total Station, as we couldn't get them to that tolerance by just measuring.  However, worth bearing in mind that our house was largely prefabricated, so we didn't have much scope for any errors at all.

Edited by JSHarris

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Just out of interest, how to you make the ducts stay "vertical " when they come up through the insulation and slab..? Got mine to do next week....

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Ours were so deep that the bends were all around 500mm down, so the  vertical bit was already well supported by the packed backfill and 150mm thick layer of crushed stone.  The MBC guys cut neat holes in the insulation around where the ducts and pipe came up, and that helped hold the flexible ducts in place.

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If you need something to strap the ducts to to keep them upright you can hammer in some rebar and grind it off at floor level once the pour has cured. I did this also for UFH manifolds.

With regards tolerance, I also stated 50mm, but this wasn't achieved in all places. While a total station was used to mark out, the process of digging the trenches removes most of the marking out.

 

I had one that was about 150mm out. This wasn't a tolerance error, but a groundworks mistake reading dimensions. I caught it before the pour and was able to joggle it over within the thickness of the EPS so that it exited the floor at the correct location.

 

Not strictly within the "all penetrations must travel vertically through the EPS" rule, but I checked with the foundation engineer and he was happy.

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15 hours ago, JSHarris said:

The tolerance I gave to my ground works guy was +50mm, -20mm on the absolute positions of the ducts and pipes coming up through where the slab was going.  He thought I was barking mad, but I really should have tightened this tolerance up a bit, as the soil pipe ended up about 10mm too close to the wall.  All our pipe and duct positions had to be fixed with the Total Station, as we couldn't get them to that tolerance by just measuring.  However, worth bearing in mind that our house was largely prefabricated, so we didn't have much scope for any errors at all.

 

Out of interest did you hire a total station or were you lucky enough to have a ground worker with one? 

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1 hour ago, Barney12 said:

 

Out of interest did you hire a total station or were you lucky enough to have a ground worker with one? 

 

Our ground works guy had one, one of the reasons he, and a couple of others, were shortlisted.  Because our plot was a steep slope originally, from which we had to remove around 900 tonnes of spoil, marking out the site would have been a fair bit harder without one.  We were lucky, in that there's an ordnance survey spot height nail in the lane right by the drive entrance, so we already had a known datum to work from, one that could "see" the whole plot and was fixed pretty permanently.

Edited by JSHarris

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On 05/03/2017 at 08:51, JSHarris said:

 

Our ground works guy had one, one of the reasons he, and a couple of others, were shortlisted.  Because our plot was a steep slope originally, from which we had to remove around 900 tonnes of spoil, marking out the site would have been a fair bit harder without one.  We were lucky, in that there's an ordnance survey spot height nail in the lane right by the drive entrance, so we already had a known datum to work from, one that could "see" the whole plot and was fixed pretty permanently.

 

Thanks. We had a 3d levels survey done as it was a requirement of the national park.

 

I'm a complete novice on this subject and so need to read a bit more on how to properly read the document and use it. My regular groundworker has a slightly more "farmer" approach to marking out (Sorry the "farmer approach" is defined by "bout ere looks right lad" :D )  I'm assuming "GPS" (see top left of image) is a datum marker but I'm not so clear on "APS" (top middle as one example)?

 

Its not helped by the fact that a lot of what you see in this screen grab was destroyed by a big ugly demolition crew!

 

2017-03-06_09-12-43.thumb.jpg.5ccaa02058eeacf83c90ee289ee65d57.jpg

 

 

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The triangles are fixed survey positions, known as control stations, in your case GPS1 (top right) and GPS2 (bottom centre) seem to be the GPS-fixed control stations, which will be to a 3D accuracy of around +/-20mm or so for a decent survey GPS.  The control stations marked "AP" may mean that they an assessed position from one or more of the  GPS-fixed control stations, fixed using the Total Station on one of the GPS control stations, I think.  All the other points are measurements relative to the closed-loop traverse datum established from the fixed survey control stations (the errors are corrected by closing a 3D loop around all the control stations, usually using a least squares method to evenly distribute any small errors).  I suspect that your site needed several control stations, perhaps because the Total Station had to be moved around in order to "see" the prism on the survey staff.  Total Stations are now pretty much one-man machines, that will automatically track the prism on the staff.  The Total Station is set up on a control station and then the surveyor can just walk around the site with the staff and the Total Station will log the 3D position of the prism on command, taking account of the height of the tripod that it's mounted on and the height of the prism on the survey staff.  Each surveyed position is marked with a "+" on the survey.

Edited by JSHarris

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@Barney12, I should just add to J's note above,  that I went round to check a random selection of pile markers each of which had been marked by a total station. I found 1 that was exactly 1meter out.¬¬ Hmmmm 

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11 minutes ago, recoveringacademic said:

@Barney12, I should just add to J's note above,  that I went round to check a random selection of pile markers each of which had been marked by a total station. I found 1 that was exactly 1meter out.¬¬ Hmmmm 

 

Sounds like finger trouble on the key pad!  The offsets have to be manually entered into the total station, plus if doing a closed traverse base line then that needs manual entry too.

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4 minutes ago, JSHarris said:

 

Sounds like finger trouble on the key pad! 

Exactly, I wrote the post to suggest that a quick dirty check is always worth it.... 

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