Ground bearing slab over shallow drains

[garyo]

Hi Chaps,

The drains around the back of my house are fairly shallow. This has led to a couple of couple of drain runs under my new kitchen extension that are also fairly shallow.

I'm at the stage of putting down hardcore, and I can't really see how I'm meant to prevent any loading on the plastic pipes.

My ground makeup is:

150mm hardcore
50mm sand
100mm PIR
100mm concrete slab.

The invert of the plastic pipes is around level with the bottom of the hardcore. Should I just encase them in pea shingle, therefore giving them a 50mm pea and 50mm sand covering, and lay the PIR over the top. Will the slab and PIR then act as the lintel to my BCO's satisfaction?

Thanks

Gary

See photo below - ignore the chunks of bricks - I've been considering building rough 'walls' with mortar to act as shuttering to separate the pea from the hardcore:

 

[23vc]

That's what I did, despite the original plans saying "encase drains in concrete" I was told on good authority (on here) it's not necessary. Assuming you're not talking about under any walls, just under the sub base/slab. I'm sure you're good

 

[garyo]

Cheers. I've just spent a couple of hours making walls around them with chunks of hardcore and strong mortar so I'll fuss a bit less tomorrow and just get on with it.