Drainage through raft

[sblewer]

Hi Guys, new member here, so like to say hello!

I have a question for the experts if I may.

I am just starting a single storey side extension to my house, and will be installing a new downstairs loo/shower room in the extension.

i have had several meeting with Building Control, regarding my footings and ground conditions, and also to discuss the new drainage line I need to put in.

I have had to have a raft foundation designed, due to poor ground conditions, and they will be 750 deep. I have actually dug my footings out to a depth of 980, a we did not find out about the soil conditions until the BCO came and did the first inspection.

My nearest manhole has an invert depth of 950mm, and is approx 10 metres away from where the new soil stack will go.

Anyway, here are my questions:

1. After getting permission from BCO, my drain will pass under the slab, and i have dug the trench for this, but my question is, what do I use to fill it back in, before I pour the concrete? Normally you would use 10mm Pea Gravel to form the gradient, but if I still use that, how do I stop it all falling out, as the ends of the trench open up into my footing trench?

2. Where the new drain line passes through the footings of my raft, what do I do with the pipe. I can't lintel over it, so I was wondering if I ran my 110mm pipe through a length of 160mm, and put rocker joints either side of the footing, would this work?

Any help on this guys would be gratefully recieved, as I need to get on with this, this weekend, ready for the concrete next week.

cheers

Steve

[lutonlagerlout]

welcome steve nice OP,
i am doing an exact same type job as this on an old brickworks in luton
we dug 2.8 M before we realised there was no good ground at any depth,so same as you we had a raft designed
i cannot understand why yours are 750 deep,we had a 300 thicks slab c35 concrete with a 450 by 450 toe all round with the 7 mm mesh in side it
we did the drains first and we had the stack pipe etc coming up in their correct positions,then we carefully cut the mesh to slot over the pipes,they were encased in 100 mm of 10 mm shingle with type 1 to ground level,the raft is supposed to spread the weight so it should be fine
cheers LLL