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As you would usually do, fill it with type1 and compact every 10-15cm of fill and then add more and compact. THen build up the sub base as you would usually do.
It would not cause problems if it is compacted enough with a decent compactor - Obviously dont use a cheap / lightweight compactor make sure it has 50kn+ of force.]
Personally I would not of dug out the clay on drainage alone, I would have left it if it was firm and compacted, perhaps compacting it more. The drainage should not be an issue as future water ingress should be inhibited by a water tight patio, with the water running off to a drain.
I assume your a DIY not a contractor?
Hello David - thanks for your reply. DIY yes :)
The area with poor drainage was where the artificial lawn would be. It is the back of the garden where there is a slope towards too.
I am adding 100mm of type1 across the whole surface, which may have been ok anwyay, but I wanted to be sure that there wouldn't be drainage issues. It was taking 12 hours to drain around 1 inch of rainwater.
I'll be hiring a compactor yes - thanks for the tip on required force. I have plenty normal soil left from the rest of the digging. If I fill the hole with that and compact is that likely to be alright? or is type 1 preferable? I've been reading a lot about this and some folks seem to suggest compacted type1 is not that good drainage wise and recommend 20-40mm aggregate with no fines.
A 20-40 clean stone would drain much better but will not really compact and so isn't an ideal base for paving.
Type 2 or type 3 may be more suitable but has larger aggregate size and so needs a heavy vibrating roller to compact it properly.
Don't put the soil back in. The absolute top job would be to fill the deeper area with 20-40mm and then cap it with a geotextile membrane and then 100mm of type 1. This would solve both the drainage and paving sub base requirements but cost a little more.
Hello Simon - thanks for your reply.
Sounds like a plan. I did a test and the hole is draining half an inch an hour. I may dig slightly deeper to see if there is more clay.
As for the membrane. I was planing on these right enough. I've seen two different (at least visibly) types of these. One that is grey/white and looks like a thin fabric, and another that is dark green and looks more substantial. Are either of these fine, or are each suited to different requirements?
Cheers.
Simon Smith said:
you want to use a free draining geotextile like terram 1000, multitrac 1000 or an equivalent.
Thanks Simon.
Attached is an image of the area I've dug out.
Should I be digging this square / right angles before laying the membrane and stone, or is a tapered edge better? Should I be compacting the surface prior to laying stone?
I should have said - it is just rainwater drainage that is the concern.
To the far left of the photo you will see small pool of water. This hasn't drained at all in 24 hours, so I need to dig that area too.
Cheers,
John.
go ahead and fill in a couple of inches of the clean stone and compact it. Then give it another few rumbles once its all in. Clean stone doesn't really compact which is why its a good fill but it will slightly ram it into the subgrade so its worth giving it a whack early on.
Then your membrane and your type 1. Comapct the 100mm of type 1 in two lifts, so compact to refusal at 50mm then 100mm.
As the for membrane make sure it covers the clean fill completely. It doesn't need to be flat, its purely to stop type 1 filtering away into the clean stone.
It's thick grey clay and a bunch of bricks at the area where there was no draining. I'm hoping digging it all to the same depth will give a good flat area to drain away from.
where do you live ? why dont you get a pro-landscaper to do it for you? if your doing artificial turf etc also?
whats your occupation?
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