Clay under permeable block paving - Advice on what method to build pbp drive

[Clarely]

Hi - we've dug a test pit 400mm x 400mm x 400mm & filled it full of water, after 24 hours the water was still at the original level. So my question is, with the council saying, yes build Permeable Block Paving drive (so we can have a dropped kerb), will it actually work if we use 4-20 sub base and then 6mm on top of that? Or will clay like this make it impossible?

And if it's not a good idea, then what do I do? Any ideas would be great.

We're putting a linear drain in at the bottom of the 1:8 slope. I'm worried that building it as permeable will just mean that water sits underneath it & then wells up out of the blocks.

[Clarely]

I'm wondering about using MOT1 and sand rather than 4/20 and 6mm. Any thoughts from anyone please?

[seanandruby]

here9
There is loads of detailed information on the pemeable and suds index pages. It may be you will have to connect to the swd as a last resort.

[Tony McC]

DTp1 (the term we should be using for MoT1) is NOT suyitable for a permeable pavement. It just doesn;t have the permeability nor the void space to provide storage capacity.

If ground tests show the sub-grade is, effectively, impermeable, the council may have to consent to you using a standard (ie: non-permeable) construction or a highly compicated overspill version of a permeable pavement, but only they can decide.

Document the standing water and present it to the council. It could well be easier for them to take the 150 quid or so from you and grant permission for the standard construction.

[Clarely]

Thanks. My neighbours have permeable, but also said all their water goes into the sewers! Wondered if it had been constructed as permeable, but it just doesn't drain. Very odd.

[Tony McC]

There is an option for permeable with overspill, as I mentioned, but only the council can grant PP for such a construction.

In essence, the collected surface water is first given a chance to escape to ground but if the volume of water is greater than the ground can cope with, then the excess 'spills over' and goes into a sewer.