Protecting underslab foul drain

[WWilts]

Underslab foul drain will run above trench fill foundation alongside internal wall.
How to achieve bedding and covering?
Perhaps lay another line of blocks parallel to the wall, for the purpose of forming a narrow "trench" in which the drain can be bedded and covered with pea gravel? If that's ok, how wide/narrow a "trench"?

[tonyshouse]

Surround with pea shingle will be all that is needed long term, test before covering 

[WWilts]

1 hour ago, tonyshouse said:

Surround with pea shingle

Yes, wondering how to hold the pea shingle in place. 
Option A is to build a stub wall on the footing (1 leaf of concrete blocks) parallel to the inner wall. Then pea shingle between the 2 walls to bed and cover the drain.
Option B is to backfill the footprint with hardcore, compact well, and then excavate a narrow drainage trench above the trench fill footing. Then pea shingle in trench, bed and cover drain.

Perhaps there is an Option C.

 

[markc]

Either blocks or soil to form a bund that will hold the shingle in place

Edited August 28, 2021 by markc

[WWilts]

34 minutes ago, markc said:

Either blocks or soil to form a bund that will hold the shingle in place

Yes, blocks have advantage of not absorbing or shedding much moisture. Won't move much

[Conor]

Lean mix. Used all the time for this sort of thing. Cheap and easy to work with.

[WWilts]

38 minutes ago, Conor said:

Lean mix

In form work to hold it in place? Or does it just stand on its own in a heap?
And covering drain or just bed and bench?

Edited August 28, 2021 by WWilts

[Conor]

Bed and cover, use as you would normal dust / gravel for pipe trench fill. The public surface water sewer that was installed alongside our founds was done exactly that way. Bed of lean mix ontop of our loose stone backfil, and pipe was covered in more. Remaining levels brought up with loose stone.

[WWilts]

13 minutes ago, Conor said:

Bed and cover,

Attractive prospect.
Limestone brash soil
Only concern with encasing in concrete was movement of ground (swell or shrink) & drain joints potentially failing. But limestone brash might be sufficiently stable for encasing drain in concrete

[Dave Jones]

haunch with conc every 1.5m to comply with building regs. If you have block and beams above you can get hangers to hang of the beam to suspend the pipe from.

[Russell griffiths]

Bed and haunch in lean mix concrete, full bed, never bed on just pads and don’t hang from hangers unless visible, as it will droop leaving sags in the pipe. 

[Dave Jones]

47 minutes ago, Russell griffiths said:

Bed and haunch in lean mix concrete, full bed, never bed on just pads and don’t hang from hangers unless visible, as it will droop leaving sags in the pipe. 

 

no it wont, rubbish.

[WWilts]

No block and beams, no hangers.

But is it ok to encase in lean mix? Not just bed or haunch, encase fully?

Edited August 29, 2021 by WWilts

[Russell griffiths]

On 29/08/2021 at 09:45, Dave Jones said:

 

no it wont, rubbish.

Yes they do, if you hang a pipe from hangers and go back in 10 years they look like a banana 

put a piece of pipe in a rack for 6 months and go and get it out, again it will look like a banana. 

[Dave Jones]

1 hour ago, Russell griffiths said:

Yes they do, if you hang a pipe from hangers and go back in 10 years they look like a banana 

put a piece of pipe in a rack for 6 months and go and get it out, again it will look like a banana. 

 

nope. hangers every 1500mm and its perfect.

[WWilts]

Amazing to see the cognoscenti discuss things.

 

But please, is it ok to encase (not just bed and haunch) the drain in lean mix? Bearing in mind that the soil has medium to high permeability (unlikely to heave or shrink).
 

[Dave Jones]

48 minutes ago, WWilts said:

Amazing to see the cognoscenti discuss things.

 

But please, is it ok to encase (not just bed and haunch) the drain in lean mix? Bearing in mind that the soil has medium to high permeability (unlikely to heave or shrink).
 

 

yes will be fine. BC only require every 1.5m though.

[Conor]

16 hours ago, WWilts said:

Amazing to see the cognoscenti discuss things.

 

But please, is it ok to encase (not just bed and haunch) the drain in lean mix? Bearing in mind that the soil has medium to high permeability (unlikely to heave or shrink).
 

Again, yes. It is done all the time in the civils world. I would encase to the joints at either end of the pipe you are encasing to at lease 5x diameters.

[WWilts]

24 minutes ago, Conor said:

at lease 5x diameters

Underslab will not permit that height of concrete. Encasing till the undersurface of the slab/DPM will hopefully suffice. Above that will sit the slab anyhow.

Edited August 31, 2021 by WWilts

[Conor]

I mean laterally, along the pipe. E.g if you are encasing a 6m run of 110mm PVC, continue another 550mm past the joint to the next pipe on either end. Will prevent any differential movement.