Block Paving Drainage

[SteveC]

First of all can I say what a brilliant Web Site this is :)

My problem relates to drainage on my soon-to-be block paved drive. I've been through all the D-I-Y pages etc and followed the Hints & Tips gven etc. The problem is at the front (bottom) of my drive.
The original tarmac drive(s) had been down since the 1930's when the houses were built. I removed two layers of tarmac and checked sub base etc. All OK, shouldn't get any more movement in the base.
I've bedded a soldier course all around the perimeter etc, and infilled with sand.
However, we have just had a days heavy rain, and I've realised that there is water collecting at the bottom of the drive "within" the soldier course, and all the sand within is waterlogged. The soldier course at the bottom is level with the pavement, which means that the bedding sand is lower, so I obviously need some type of drainage( or do I?).
I'm waiting for the sand to dry out before I start laying the blocks, but if I don't put any drainage in at the bottom of the drive, what will happen when it rains? Most of the rainwater will run off the surface anyway, but what about that which penetrates down into the sand layer etc?

[84-1093879891]

You're worrying unnecessarily, Steve. Surface water may well be acccumulating at the lowe rend of your drive at the moment, but that's because there's plenty of room for it to do so. Once it's all paved-in, there's nowhere for the water to sit, and so it moves on, as it were.

Yes, some water will be retained for a short period by the sand bedding, but there is only so much water that can be held in voids between the sand gains, and once they are full, any further surface water will not be able to penetrate, so it will run off over the surface. Gradually, any retained water will seep away through the sub-base, leaving only that water which is held by capillary action, which is natural for a sand.

What happens over the longer terms is that 'fines' are washed into the sand bedding and thanks to gravity, they end up at this low point, where they reduce the number and volume of the tiny voids (interstitial spaces, as they are sometimes called), so even less water can be retained by the bedding sand.

There are hundreds, probably thousands, of block-paved driveways in the same situations as you describe, and they manage to survive without any additional sub-surface drainage system, so I reckon your's will be fine, Steve. :)

Good Luck!

[SteveC]

Thanks Tony
It's reasuring to know all's well.
Over the weekend it was warm and sunny, so the sand dried out a lot. So I've got all the blocks laid, and only the "cutting-in" bits are left to do now. Although today it's again pouring with rain, and I'm wondering now what sort of time do I need to leave the blocks before I can use a "whacker" plate on them?

Thanks again for your help. :)

[84-1093879891]

As soon as poss! You mentioned previously that your edges are in and have set, so, as soon as you've finished cutting-in, and the weather is dry enough to sand-in the joints, you can get the vib plate going on the lot! :)