Resin bound drainage / suds hybrid/drainage puzzle

[Aspire]

Hi All, Any advice would be really helpful...

I have client that wants me to put down a new drive for him. The existing is gravel and was put down with the house 15 years ago. As such it is in pretty good nick with no dips and (sods Law) is actually almost perfectly flat (no Falls). He wants a mix of slabs and resin bound gravel. My plan was to take up the lot and put down geo textile, 2x 100mm layers of type 3, then lay the slabs (40mm stone flags) on 40mm of wet conctete with slurry primer strait on to sub-base with Rompox jointer and put down a binder course of 60mm large aggregate permeable tarmac with 18-25mm resin bound over.

I was going to lay the slabs to a slight fall so water drains onto resin and through. The problem is at 284m2 this equates to about £40k and I suspect customer is going to cough at this a bit. I am wondering if there is some way of leaving down some of the original type 1 and only put 100mm of type 3 down under the binder course. This would allow much less excavation, less muck away and expensive type 3 and hence lower the cost.

My question is will this drain ok (soil type is sand & gravel but there are rivers nearby and water table may be high ish) or will the type 1 act as an impermeable layer and cause the drive to flood. I had the thought that there would still be all the area above the type 1 to act as a soak away (100mm type 3, 60mm tarmac binder and 25mm resin bound) but obviously the water could only occupy 30% ish of this area due to aggregate content.

If not I was then considering a kind of SUDS hybrid where somehow i put in some secondary drainage to take up whatever does not soak through. Ie. perforated pipe sat on top of type 1 layer (within type 3 layer) to take water away or possibly Aco channels? My only concern with the Acos is what level you put them at...? If they are at surface layer then the water will go strait through the Resin bound (and other substrates) and will hit the side of the Aco rather than going into them...

Any thoughts you have would be a great help. Thanks, Oli

[lutonlagerlout]

Oli
if there are no falls introduce one,if needs be in the middle
we all know what happens to flat paving
LLL