The Brew Cabin

I am digging the foundations for a conservatory (full height glass).In the corner of the area is an inspection cover which leads down to a number of Plastic pipes. The inspection hatch does not cause me a problem as it will be just outside of the conservatory, but the drains do occupy an area where my footings/floor is due to be, all be it a good 12 inches below my intended footings depth.
My questions is how to deal with these drains (without moving them). The house itself has been built on a hill and so has been subject to large amounts of in-fill on the garden side - a sand/light clay and large flints (up to 200mm) flints and is very soft to dig.
I intend to reinforce my footings and concrete slab floor to give stability but should I

1) concrete in the drains underneath as well (I am concerned about setting all the joints in concrete with room for movement.
2) backfill with the material I removed and create some form of lintel across the area,
3) Backfill with the material I removed and rely on the raft effect of the reinforced footings and concrete slab to support the weight of the conservatory (it is going to be fixed to the wall as well !)
4) As 3 but surround the pipes with some form of granular infill first ?


Suggestions ?

Without seeing the actual layout of the site, Nick, it's hard to say what would be the best solution.

Have you though of asking your local Building Control Officer to pop down, take a look and offer you their advice?