Foundations and bridging over drains

[r_c]

(Disclaimer - I am not a builder, so please excuse my lack of knowledge and possibly use of wrong terminology, etc.)

We have had piling and a ring beam done, required because of the close proximity to a 5m deep drain (shown on the right of the plan running down side of house). The piles had to be at least 1m from the deep drain.

When our (new) builders were preparing to connect a new pipe to the drain that passes underneath the house (see green arrow) at a depth of about 1m, they were surprised to find that it looks like the piling company (who installed piles and ring beam) had not bridged the pipe. They deduced this by sticking a screw driver through the polystyrene and hitting a hard surface. The piling contractor was asked to visit the site. On site, when asked why there was no bridge, he replied that it was not needed. This surprised the builder, and engineer (who are both new to this project).

The pipe at the point of the green arrow is about 1m below surface.

Is the piling contractor correct when he says a bridge is not required?

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[russellsmiler]

Couple of things to consider.
I assume you have building control on board? they should have a discussion with contractor on your behalf if possible.
With regards to bridging the pipes, I would determine if the pipes have been completely cast into the ring beam, If there is a polystyrene sleeve that allows for settlement of the whole foundation + deflection of ground beams when masonry walls and roof load onto it (your structural engineer will have the calcs so should be able to tell you the amount of deflection (it wont be much)) then I wouldnt worry. If there is no cushion then this is what to consider. I cannot tell if the pipes are clay, if they are then you may need to introduce "rockers" either side of the ground beam at each entry and exit of the drain, A rocker is a less than 600mm length of pipe, its basically to allow for movement without cracking the pipe. If the pipe is plastic then I would make sure there is good granular material as a bed and surround again 600mm either side of pipes entry and exit through the ring beam. Another thing is how much fall is in the run, hopefully is as a good fall and could accommodate settling at the points through the ground beam.

Your piling contractor will of had a duty to protect this pipe, the engineer who may be new to the project should have an understanding of this, also quite suprised that it is not given a mention on the drawing.

 

[russellsmiler]

Just realised that i can zoom on the pictures.
There is a note saying that 225mm of cellcore to be placed under ring beam in proximity of mains sewer. Is the sewer shown by your arrow the main sewer?? I believe that this is what the engineer is calling for in the proximity of your pipe, however if the pipe level is higher and is in the ground beam (which it is) then there should of been dialogue amongst all parties, Engineer, piling contractor, building control. what I wrote above still applies.

 

[r_c]

Thank you for you replies. This drain is a public drain as about 4 or 5 neighbours drains flow into it.

I assume you have building control on board?

The new builders have questions, and have asked building control to visit the site as building control signed all this work off.

I just assumed they are clay pipes, the original 1930s pipes. The piling was required because of the 5m deep drain, shown on the right, and that seems to be what the 225mm of cellcore note relates to. There does not seem to be any specific instructions regarding the pipe in the photo.

then there should of been dialogue amongst all parties, Engineer, piling contractor, building control.

I'd love to know if there was a dialogue. Unfortunately our original builder fudged many things, and he and the architect appeared to cover up for each other. We were told that there were no issues with the piling, even though our new builders have discovered that one of our foul drains (not even shown on the plan?!?) was bunged up as the ring beam goes straight through it. So we have questions about that too, but that might another posting ....

 

[russellsmiler]

Hi
Yes have looked again and the drawing does indeed refer to the cellcore being in relation to the main sewer on right of drawing.
Am not sure at what stage you are at with your building, I can see blockwork, have you got the ground floor in yet, is it accessible,??

 

[r_c]

The extension has been built, and screed with UFH installed over the block and beam

 

[^woody^]

This drain is a public drain

Do you have a Build Over Agreement in place with the water company? If not, its unlawful.

All drains need to be bridged, so that if the foundations move, the pipes don't crack. Alternatively, there can be a flexible joint each side of the built in section of pipe.

 

[wessex101]

I think this talk of "bridging" is confusing the issue. The ground beam is in effect a giant reinforced concrete lintel so that takes care of the bridging issue. What I think the problem is sleeving the drain, did they cast the ground beam directly on top of the drain or did they sleeve it with compressible material?

I suspect this mention of sticking the screwdriver through the polystyrene and hitting a hard surface suggests the former. So any settlement of the ring beam/piles will probably crush the pipe or at least affect the fall of the drain. I assume that is why the engineer specified 225mm cellcore under certain ground beams.

I would suggest that the drain is exposed where it passes under the ground beam to see exactly what has been done rather than just poking screwdrivers into the polystyrene. Depending on what you find you can than take a view on whether any settlement is likely and what the potential risks might be.

 

[r_c]

The piling contractor has now visited the site. He says that there is a 2mm movement gap around the pipe. Building Control came out also and basically said that as there is a clear run, and it is fit for purpose. (I was not present at either meeting, so I have used italics as I did not hear their responses first hand.) I am struggling to understand what value building control provide in general ... but that's another issue I guess.

Do you have a Build Over Agreement in place with the water company? If not, its unlawful.

We (the client) have no document/letter/reference from Anglian Water. Looking back through emails I found in response from the architect to a question I had about Anglian's requirements: "i will be sorting anglian requirements. worry ye not"

I think this talk of "bridging" is confusing the issue.

I think you are right. Bridging and the material around the pipe are two issues and I confused the two.

This probably isn't news to you, but I have come across General Requirements regarding Building Over or Near the public sewer on Anglian Water's site, which I am struggling to see how it could have been satisfied.

Where the sewer is to be built over and is passing through the wall of the building, the foundation must bridge the sewer with a suitably designed reinforced lintel. There must be a minimum of 150mm between the underside of the lintel and the sewer, with some form of compressible material placed between the sewer and the lintel. The foundations on either side of the sewer must be constructed to a level below the pipe bedding and the foundation must be adequately separated from the pipe surround/bedding material.

The piling engineer appears to be concerned about the 5m deep sewer on the right, and has forgotten any mention of the (green arrow) sewer.

 

[^woody^]

2mm gap for movement is nothing. The building will settle more that that and will bob up and down 10x as much through the seasons.

I can't understand how building control could approve such a small movement gap, or let you carry on without any required build over agreement in the first place.

 

[wessex101]

The piling contractor has now visited the site. He says that there is a 2mm movement gap around the pipe. Building Control came out also and basically said that as there is a clear run, and it is fit for purpose. (I was not present at either meeting, so I have used italics as I did not hear their responses first hand.) I am struggling to understand what value building control provide in general ... but that's another issue I guess.


We (the client) have no document/letter/reference from Anglian Water. Looking back through emails I found in response from the architect to a question I had about Anglian's requirements: "i will be sorting anglian requirements. worry ye not"


I think you are right. Bridging and the material around the pipe are two issues and I confused the two.

This probably isn't news to you, but I have come across General Requirements regarding Building Over or Near the public sewer on Anglian Water's site, which I am struggling to see how it could have been satisfied.


The piling engineer appears to be concerned about the 5m deep sewer on the right, and has forgotten any mention of the (green arrow) sewer.

I suspect the piling contractor is bull ****ting you. How exactly did he achieve this "2mm" movement gap? Perhaps he wrapped the pipe in 2 layers of toilet paper, the extra thick quilted stuff of course. I've never heard anything so ridiculous. Building Control are not quality assurance inspectors, getting this sorted is down to you do not rely on them. (although I would say the work appears to contravene building regs so I don't know why they are being so useless)

Expose the pipe and see exactly what has been done. It would appear not to comply with the engineer's piling details in respect of the 225mm cellcore under the ground beam and does not comply with Anglian's build over requirements. With the pipe exposed you might like to ask building control to re-inspect and throw in the little nugget of suggesting you might complain to the local authority ombudsman as they appear to have signed of work that contravene regs.

The piling contractor has screwed up but it is up to you to provide the evidence or employ someone who can as it seems he is not going to put his hands up and admit to it.

 

[r_c]

it is up to you to provide the evidence or employ someone who can

Where do I start? I'm having enough trouble finding a solicitor who deals in building litigation.

 

[wessex101]

In the photos someone has already exposed the drain, all that had to do was cut away a small section of the polystyrene/cellcore to expose the drain where it passes under the ground beam and take some photos. I don't know why they were messing about poking screwdrivers into it rather than just looking at it properly (I'm not convinced your builder knows what he is doing either).

You don't need a solicitor, the engineer should be able to inspect and if necessary write a report on any defective work (and possible lack of build over agreement). If the engineer determines that remedial work is required and if the piling contractor still will not accept responsibility then it is probably a Moneyclaim/Small Claims Court action. Similar action against "architect" if he "forgot" to get the build over agreement.

 

[rssteve]

Sorry to go off topic but interesting post as piling information doesn't come on here often. I have a few questions if you dont mind. Did they use mini piles? How deep did they need to go in the end? Whats your ground like? Do you mind mentioning cost?

Steve

 

[r_c]

Did they use mini piles? How deep did they need to go in the end? Whats your ground like? Do you mind mentioning cost?

I cant find the actual depth numbers, but I am have a feeling that some of these went down over 10m. But I cant find the information that I based that on, so ... I could be wrong. I hope this is what you were looking for ...

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But this dog's breakfast only gets worse. It looks like the architect did not do a drain survey and the ring beam goes straight through the house's drain! I'll probably start another thread for that to ask advice on dealing with this. In the plan above I have attempted to show (with a pink highlighter) a missing drain (now blocked) and a very badly drawn sewer that goes under the building. The piling engineer is not at fault - he has shown the drains and sewers as indicated by the architect.