Foundation Infill

Hi All
I just want to get a few opinions. We are building a split level bungalow and our contractor is filling in the foundations with the origional excavated material so its basically mostly clay that has gone in with some rock/stones. I thought that a layer of auctual stone woud have to go in, then clay then a lighter stone. Does this sound like normal enough practice? Some of the foundations were 5 foot deep so there is a lot to be filled.
Thanks

Entirely depends on the suitability of the fill material. The best material for this is a 'well graded material'. i.e. a varience in stone aggregate size so it compacts well and pores are filled.

If the clay is dry enough it may well be ok for the bulk fill then you would need a decent material for the top say 200/300mm (Cl 804) compacted onto which your slab will sit.

If unsure of the quality of the material your Engineer/Architect should advise.