Laying a Type 1 Sub-Base

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Hi guys,

Just wanted a bit of advice on this. Fairly (very) new to garden landscaping but I'll give anything a go after a few Youtube video's. I'm at the stage where it's planned and will probably begin buying materials next week, to then begin the first stages in mid-February. This is one element of a larger project, but the rest is irrelevant.

Essentially, I'm laying a 2.31x2.31m sub-base. It will support an item that will weigh 1800kg with dimensions of 2.2x2.2m.

My plan at the moment is to dig the hole (of course), lay and compact 100mm of Type 1 MOT, and then place a pad on top of that which the manufacturer states can support 420 tonnes per square metre. The pad is usually able to be placed just on grass, however the manfacturer for uneven and/or areas with drainage issues to dig it out and use 50-70mm of Type 1, so I've gone a little more.

So, Type 1 for 100mm, a weed membrane, then the pad, and the gaps within the pad is filled in with gravel. Is the fact I have typical new build clay soil going to impact this? I need to make sure it's secure, I don't want it to sink! Would you make any adjustments to the process, or even go for more MOT?

Edit: Just to add, eventually, in the months after I'll be adding a decorative stone border around this area. Will this effect the Type 1, or will the fact I've compacted it in mean that even when I remove the soil around it and replace with stones that it'll be structurally sound?
 
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You don't need a weed membrane on top of 100mm of stone, you could put a geotextile type membrane under the stone for extra strength, but probably not needed.
What is the item, (hot tub?) is the weight evenly distributed?
You will need some sharp sand on top of the hardcore to level it out.
 
You don't need a weed membrane on top of 100mm of stone, you could put a geotextile type membrane under the stone for extra strength, but probably not needed.
What is the item, (hot tub?) is the weight evenly distributed?
You will need some sharp sand on top of the hardcore to level it out.

Yes, sorry had it wrong way around. Membrane down with type 1 on top of that. I've read it's useful to prevent the stone mixing with the soil, especially in waterlogged clay soil like mine.

Yes, it is a hot tub that's going on top.

Interestingly, the manufacturer of the pad that it's going on didn't mention the need for sand, just type 1, but I am aware sand is used when going through the similar process for fitting a patio or similar. Is it not easy to get the hardcore level without sand?
 
Why not prep the area to include the perimeter of stone in one go and sit the form work for concrete pad in the middle?
 
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Why not prep the area to include the perimeter of stone in one go and sit the form work for concrete pad in the middle?
The stone perimeter isn't going to be just around this square area, it flows to various other areas (they just weren't relevant to this post so I didn't mention) so it's easier to do it all at once. I'll also be putting french drains in the stone areas.
 

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