Shallow drain under driveway

[Crofter]

My existing house, built in the 70s, has quite shallow foul water drains. The pipe runs across the road and is only about 300mm below the surface.
Now this would be no problem except I am building another house over the road, and will have to put the new driveway over the ground that the soil pipe is in.
Currents regs ask for a 900mm cover depth, but I can't comply with this. Marley have some useful info about using a reinforced concrete slab, which it says is better than pouring concrete around the pipes, but this presumes that the slab can bear on virgin ground.
Unfortunately the piece of ground in question is built up, made from the spoil left from building the existing house 40 years ago. So I'm not sure if the slab method can be made to work.

I could put a backdrop chamber right at the edge of the road, allowing me to drop the level of the pipe, but I don't want to do that cos the driveway bellmouth will end up being a passing place (single track road) and everybody and their dog will drive over the top of it. At least if it's in the middle of my own driveway it will only get a car wheel either side.

[seanandruby]

If old drainage it should be clayware, therefore it is s minimum of 400 in a drive. After 40 years the ground should be as compact as it is going to get. I would encase the pipe in concrete and put in flexible joints at every coupling incase of movement. That should do the trick.

[Crofter]

Thanks, sounds fairly straightforward. The pipe is plastic though, not sure how common that was in 1976.

I do have some large reinforced concrete slabs (lids off a septic tank)- was wondering if it would be a good idea to lay these across the top of the drain run, obviously not directly in contact with the pipe itself.

[seanandruby]

Usually if you use slabs you create a shelf to set them on so the weight is spread.