Hmm, strange one. I take it you didn't ask the person who said it what red soil was,where you could get it and why you should use it then? Which means I can make an educated guess, but don't really know ...

The only 'red soil' I know about is usually formed in moist, temperate zones, often in forests, and is usually poor in nutrients but high in iron, and is often difficult to use for cultivation purposes. It's possible whoever said to use it was thinking that it would serve as subsoil, with at least a foot of good topsoil on top, but I can't know why they said it really. I wonder where this person who said you should use it thinks you might be able to get it from though... More info about red soil here

http://www.brighthub.com/environment/science-environmental/articles/64197.aspx

Maybe someone else will give a better answer...

Thanks. I'm not sure why he said that, it was my Mrs that spoke to the guy - i'm ordering a large amount of Type 1 from the quarry. Perhaps the notion of topsoil right on top of hardcore was a problem. I had considered that the type 1 would offer TOO MUCH drainage and the topsoil couldnt retain the nutrients needed; the red soil may slow this process. I am considering putting red soil down too, then topsoil, then the grass. I'm concerned that this top soil kills my grass - does it have any benefits or poisons that may kill off the grass?

Andy

Not topsoil, no - you need good topsoil for growing plants, topsoil's the bit that has the most organic material along with bacterial, fungal and microbial activity, and the more of those the better. Usual arrangement (or profiles, as they're called) for layers of ordinary soils is (hopefully) a good foot of topsoil with a layer of subsoil of varying depth beneath- the subsoil may be clay or made up of other constituents, but doesn't generally contain much humus rich material, unlike topsoil. What's under the subsoil varies from region to region - could be granite or other bedrock, or a stony/sandy layer and so on.

If the topsoil isn't great, you will find plenty of weeds arriving over the next few months and it may also be heavy and stony. Certainly, if you can get red soil, putting that underneath is probably better than just aggregate, but I'd be asking where it comes from, this red soil...

Thanks,

I don't think that I'd use quarry type1 for gardening purposes - Type1 is graded crushed rock used for road building.

I would consider doing a bit of re-shaping of the land around this 'void' to create a slope down or a terrace/step and using the material dug out mixing it with more organic material and some coarse gravel for drainage to provide a subsoil.

I would not used any sort of hardcore in the filling of the hole unless you are on heavy clay and need it for drainage as, in time, the soil will filter down through the hardcore and the surface will slump. If hardcore is cheaper than soil then the two should be mixed together before you put it in the hole, otherwise I would just use soil.

i'm just curious as to why you have such a void?