Permeability of hardcore

[Don44]

Hi,

I'm planning a gravel driveway and am unsure about the drainage requirements.

The land has exceptionally good natural drainage thanks to very sandy soil and being located on the crest of valley. As a result there's no need for a soak-away as long as the water can get to the soil.

If I build a concrete rimmed driveway with a 20 cm thick layer of hardcore (0/25) and 3 cm of decorative gravel on top, will water be able to pass through the hardcore into the soil underneath? Otherwise I was thinking of giving the hardcore a gentle slope and on the lower side leave a gap which is filled with 10-22 gravel which the water could escape through (see image).

Does this make sense or is it madness?

 

[endecotp]

You'll no doubt find the answer here: http://pavingexpert.com

 

[r896neo]

You'd ideally use type 3 as a permeable base. That is what would would be spec'd as the sub base for a permeable paving system.

Type 1 is actually permeable just not as free draining as type 2 or 3. The problem with type 3 is that it has some large stone in it and can be difficult to compact well without heavy duty equipment like a vibrating roller. A normal vibrating plate would not be up to the job.

In my opinion if the sub base is free draining your 0-25 will absolutely be fine. If you can get something like 0-50mm it would be better.

 

[Don44]

Thank you for the helpful replies. I had a read through the paving expert website and it only briefly mentions permeability, however it's still a very useful site.

You'd ideally use type 3 as a permeable base. That is what would would be spec'd as the sub base for a permeable paving system.

Type 1 is actually permeable just not as free draining as type 2 or 3. The problem with type 3 is that it has some large stone in it and can be difficult to compact well without heavy duty equipment like a vibrating roller. A normal vibrating plate would not be up to the job.

In my opinion if the sub base is free draining your 0-25 will absolutely be fine. If you can get something like 0-50mm it would be better.

This is good to know! Unfortunately I already have the 0-25 on site so it's too late to switch for this project. I'll go for 0-50 next time.