Hardcore base

12 Jul 2008
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United Kingdom
Just looking for a bit of advice around laying some hardcore. My house is on a pretty steep hill and consequently the garden is sloped. There is a big step down of over 1M from a small patio area to the first level of the garden (there are 2 levels).

When I bought the house there was decking to extend the patio out into the garden with its own steps down. We took this down as it was rotten and neglected. Underneath was a huge mount of earth which I have taken away. I now have a flat, empty clearing in which I intend to place Gabion baskets of 1M height in a row of 2 to extend the patio out by 2M. I will use Gabion's of varying depths to create steps.

I have cleared the area to a depth of 115MM down from the existing patio to allow for a 100MM hardcore layer underneath the baskets and some room for decking over the top of the baskets, this is to allow for the depth of decking boards over the top of the basket in order to try and get the 2 floor levels flush with each other.

I used a string strung from the floor on the existing patio to a pole just beyond the 2M mark with a level on the string. That allowed me to measure down to the earth bellow to ensure 115MM for the whole area. I then used a ling spirit level on the ground to see where the high spots where and raked them flat.

I had to take a lot of earth away in the area nearest to the existing patio but due to the natural slope of the garden much less to towards the far end of the 2M. So much so that the distance from the string to the ground bellow in this area was already around 115MM....

This means that the hardcore layer to the rear of where the cages will be sat will probably be sat above the ground. I need to know if this is ok? The only way around it would be to dig down even further but this would mean a lot more earth to dig out of the shallower part and a lot more hardcore... plus another skip etc. I also need it doing soon as possible so more digging isn't really an option.

Could I pour a cement mix onto the hardcore which sits above ground to try and set it to prevent it from moving? I can't imagine this being an issue as the hardcore will obviously be compressed. I will be hiring a whacker to to this.

Second question is about working out the depth uncompensated hardcore vs finished depth. Is there a calculation for working out how much the hardcore will compress? I will need to approach this with caution as I don't want to end up with a hardcore layer which is to thick and takes the top of the Gabion's above the level of the existing patio. A little step down is fine but a stop up would look crap. I will need a little bit of trial and error here I think so would rather add more hardcore if needed to achieve the correct height.

I understand some people don't use any hardcore when building with Gabion baskets as long as they are lay'ed onto firm level ground so it might be overkill but I would rather be on the safe side.

If you read all that, thanks! Hope it made sense. I will try and add a few pics of where I'm up to.

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I’d just lay more hardcore beyond the stop point say another couple of foot to shore up the rest. Then at a later date after you’ve laid whatever on top, bench it with a sharp sand cement fillet or put something like a sleeper down to stop any spread
How much the hardcore will reduce down when whacked is hard to estimate, depends on how compacted it was when you laid it and how firm the subsoil is. You’ll probably find some bits sink more than others and need topping up

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