drainage quiries, pipe depth

[leew2]

Almost finished an extension project and one of my last projects before it can be signed off is to lay some pernament drainage to replace the temporary buckets which I keep having to empty.

Been trying to make head or tail of part H and have looked at some online resources but still have some quiries about how to do some aspects.
I will be installing two gullies which will both take rainwater and one of which will also take waste from a basin. These will link to an existing combined sewer. I did consider a soakaway for the runoff but the building inspector recommended I put it into the sewer as the soil is unsutible for a soakaway.

I am considering using push fit PVC pipe and fittings.

Is there a minimum depth of pipe in a garden? I notice that part H mentions fields or roads but not gardens. My proposed run would be totally covered by a block paved or flagstone footpath.
for bedding is 10mm gravel sutible, laid to a depth of 100mm under the pipe and 100mm each side (300mm trench total width).
Also, is it ok to backfill the trench with the heavy clay soil I dug out of the trench? From digging the foundations of the extension I noticed the clay appeard free from stones.

Please see a rough plan of my proposed layout:



Another query is where my new drain will pass over the public sewer, do I need to do anything special here and is there a minimum vertical seperation needed here?

I am intending on using rodable bottle gullies, am I correct thinking no other rodding eyes etc are required?

The public sewer and the existing private pipe are made from clay c1934. My intention is to remove a section of the clay pipe and insert a PVC tee with a clay to pvc adaptor at each end.

 

[Hugh Jaleak]

Plastic pipe is fine, easy to use and you only need a saw and file to cut/chamfer the pipes.

Cover the pipes with a decent layer of gravel, then select the first layer of backfill, use smaller stuff first. Any sections running under an area subjected to vehicular traffic will use then i'd cover the pipes with concrete for protection as per part H.

Bottle gullies should be fine, there's no soil (W.C.) using the pipe so unlikely to block. Shouldn't need to worry too much where you cross existing sewer, just dont hit it whilst digging! May be worth fitting a small chamber where you join new to existing sewer, gives access there should it ever be needed in future.