Piled foundations and private drain question

[JackOfNoTrades]

Hi all 

For a number of reasons, I've had to opt for foundations of a reinforced ground beam supported by screw piles. There is a private foul drain running underneath the new extension and as it stands the drain will go under the ring beam, between two of the screw piles. 

 

I'm obviously planning on surrounding the pipes with pea shingle as it's going under the building, but I'm trying to work out if I need to provide any other protection above the plastic drain. If this was a traditional trench foundation I'd obviously have a lintel, but I can't find anything clear on the regs with ground beam and screw piles. The pipe will end up being around 200mm - 300mm from the bottom of the reinforced ring beam. But the screw piles will go a few metres below the drain. 

As far as I can tell it, the things I can do to support the pipe are: 

 

1. Add flexible joints to the pipe either side of the ring beam. 

2. Add another concrete slab/lintel above the pea shingle. (As in Approved Doc H for shallow laid pipes - although there might not be enough room for this between the screw piles as Doc H states minimum bearing of 300mm each side, plus 100 granular.)   

3. Nothing - the ring beam acts as a lintel sat on top of screw piles that go below the depth of the drain. 

 

Any thoughts on the above would be really appreciated.

 

Thanks all!

 

[Conor]

4. Move the drain. It's yours so may as well as you'll be digging the area up anyway. 

Edited June 11 by Conor

[JackOfNoTrades]

3 minutes ago, Conor said:

4. Move the drain. It's yours so may as well as you'll be digging the area up anyway. 

Afraid that's not possible due to where it leaves the property.  That would be the dream though 🙂 

Edited June 11 by JackOfNoTrades

[Conor]

In that case you want to span over using concrete lintels or an RC beam. 

[JackOfNoTrades]

Thanks for the reply Conor,

 

I guess what I'm struggling with is ... isn't the reinforced ground beam a huge lintel in this context? 

 

Given that the lintel above the granular infill will be in the same direction as the ground beam, does it actually protect the drain? 

 

[Alan Ambrose]

Standard paving slabs loose laid on the shingle and along the pipe - if only so you remember where the damn thing is?

[Conor]

1 hour ago, JackOfNoTrades said:

Thanks for the reply Conor,

 

I guess what I'm struggling with is ... isn't the reinforced ground beam a huge lintel in this context? 

 

Given that the lintel above the granular infill will be in the same direction as the ground beam, does it actually protect the drain? 

 

I'd check with SE. Even though the screw pipes take the bulk of the loading, the ground beam will still be designed to sit on firm ground, but over the drain you'll need to make sure there is no/minimal loading. Might mean a bit more steel, thicker concrete, or an additional screwpile closer. You really dont want an issue with a drain under your house 

[George]

Ideal would be to excavate around and provide shuttering over the drain and backfill when the concrete has cured. This is to prevent the wet concrete damaging the drain and you know the surcharge hasn't damaged it during construction.