New Foundation over existing sewer

[Montea]

Hi All,

We are in the middle of digging new foundations for a new steel frame of my house back wall and we found a 20cm (outer diamter) sewers pipe going directly under the exiting foundations (55cm below the existing house concrete slab).

The builder proposes to dig under the pipe and lay the steel beam there, however, I think this is unnecessary work as we have just enough height to do the work over the pipe.

I am looking for 2nd opinion regarding both proposals.

Please find attached both proposals below.

Thanks

 

[noseall]

There is no need to dig under the pipe. You would typically dig along side and bridge over - correct.

Big Trench

• noseall
• 12 Jun 2020

Unless of course moving the pipe is more practical.

 

[Montea]

Thanks Noseall, for the information and a picture.

Would you be able to share details of how are you planning to bridge the pipe, the size of the bedding and other details? Has your work been approved by a structural engineer?

I tried to find details and requirements on how to bridge the pipe correctly, however, I wasn't able to find the one that would provide details of the all requirements. It seems people do whatever structure engineer designed but these designers vary a lot.

The actual picture of the pipe attached.

1. Does anyone know what would be the inner diameter of such pipe where the outer diameter is ~20cm?
2. Also, would anyone be able to advise on the bridging sizes?
3. Can someone let me know if concrete lintel (in my drawing above) is required or can I put the metal rods on top of the pipe and pour concrete? Effectively making lintel manually?

 

[Ian H]

The pipe will be 6” and if you wanted to replace it with plastic so you don’t have that collar under your foundation, you will need a short length of pipe and 2 x AC6000 bandseals.

 

[^woody^]

There is no need to dig under the pipe. You would typically dig along side and bridge over - correct.

Big Trench

• noseall
• 12 Jun 2020

Unless of course moving the pipe is more practical.

Are you saying that the strip there was just bearing on 150mm of ground either side of the pipe?

 

[frutbunn]

There is no need to dig under the pipe. You would typically dig along side and bridge over - correct.

I've seen this method done on a few occasions on both public sewers and private drains, I assume it was reinforced over the pipework though.

 

[Montea]

Does anyone know the exact requirements and dimensions for creating a bridge?

 

[Hugh Jaleak]

6" pipe is likely to be a shared sewer and therefore the Water Company's pipe. Have they been consulted?

 

[noseall]

Are you saying that the strip there was just bearing on 150mm of ground either side of the pipe?

No it was widened (by hand) to 300mm each side once the lid was on.

 

[noseall]

Are you saying that the strip there was just bearing on 150mm of ground either side of the pipe?

P.S that's a 6" main sewer.

 

[^woody^]

Seems a bit dodgy

 

[Montea]

6" pipe is likely to be a shared sewer and therefore the Water Company's pipe. Have they been consulted?

I spoke to them. They haven't provided any details. Only asked for designs of what are we building and how are we planning to bridge it.

 

[^woody^]

I spoke to them. They haven't provided any details. Only asked for designs of what are we building and how are we planning to bridge it.

The water company wont design it for you. You tell them what you propose, they tell you if they think it's suitable - and you pay for the privilege!

 

[Montea]

6" pipe is likely to be a shared sewer and therefore the Water Company's pipe. Have they been consulted?

It can't be sewer as the angle is towards the house. My sewer is next to the house and going towards another house.

Everyone who saw the pipe the first time had the same idea until they have seen the angle of the pipe. Does anyone know where to get the map of the sewer system? The water company doesn't have it.

 

[Montea]

The water company wont design it for you. You tell them what you propose, they tell you if they think it's suitable - and you pay for the privilege!

That's right. That impression I got after having chat with them.