Too wet for block paving?

[mydogisbald]

Hello All,

I've just embarked on block paving my front garden to provide extra parking.

I'm planning to have a 0.5m border along the front of the house and also in front of the fence between us and our neighbour.

This is mainly for drainage as we get flooded in heavy rain due to poor soil and the fact the neighbours drive is a solid concrete slab covered in shingle with no drainage so we get all the run off.

[IMG]http://i346.photobucket.com/albums....MG]


We've had a couple of hours of rain this morning. At 4pm the test hole I've dug has still not drained. The soil is deep clay (as we found out doing our extension) Will this cause problems? Still unsure what to do for drainage wouldn't a soakaway be ineffective?

[Tony McC]

That's not an hole! It's a scrape, a dip, a bit of an hollow!

You need to dig down at least 600mm - concentrate on depth rather than width and length.

A 500mm border isn't very much, either for planting or for draiange. The wider you can make that, the more effective it will be.

You might need to dig out that border to, say, 600mm or so, and backfill with really good quality free-draining soil or a 50:50 mix of loam and grit sand to improve the drainage once the driveway is done.

Clay is always a problem, but if you think about the total area of the border and get as much depth as poss so it acts as a rain garden/soakway, you might be OK.

[mydogisbald]

Thanks Tony,

I only went down a few inches in the hope I'd only need to go so far. That takes it 400mm below the DPC of the house. Are you saying I need to take it down to 600mm over the whole driveway area?

[Tony McC]

Not specifically - but for your test hole, to determine just what the groundwater situation is like, the deeper the better.

Assuming you find a suitable sub-grade, the excavation depth is likely to be somewhere around 400mm below DPC anyway: 200-250mm depth of pavement construction plus 150mm for building regs

[mydogisbald]

We had to go down 1.5m for our extension footings and it was still clay. I've got a mini-digger coming tomorrow so it'll save my back anyway. I was thinking of putting ACO type drains in around the house but as the ground is level would this be a waste of time? Would I be better off putting them at the boundary and sloping the driveway to them?

[Dave_L]

But where are the Aco drains going to discharge??

[mydogisbald]

Into a small soakaway with an overflow into the surface water drains.

[Dave_L]

Into a small soakaway with an overflow into the surface water drains.

Ah, fair enough

[Tony McC]

Wherever you put the drainage channels, the drive has to slope towards them otherwise surface water won't flow into them.

[mydogisbald]

I got talking to a builder acquaintance (not a driveway bod) today. He's done a few block driveways in the past. I asked what depth he thought I should go down to. He said he puts down 4" of concrete straight on the soil underneath then 40mm of sand before laying the blocks.

I've seen a couple of the drives he's done and they do look good with no rutting or heaving several years on. He did my sisters drive about 3 years ago and it hasn't moved whereas her neighbour had theirs done just over a year ago using the type1 method and it's showing signs of rutting already.

I'm now unsure if I should do the same or put down an extra thick layer of type1. It will need to take 2 transit sized vans and a hatchback car.

Any thoughts?

[Dave_L]

Destined to fail I'm afraid.

[Tony McC]

You're right: he's very definitely not a driveway bod - just a driveway bodger.

Concrete straight on the soil? Pillock!

Sand over concrete? Cowboy!

This site is jam-packed with advice on how to do the job correctly. Read some of it and then you'll understand why this comedy construction is all wrong.

[mydogisbald]

Right, that's decided it then, lol.

Would a type1 base of 150mm be enough for the intended traffic or should I up it to 300mm or maybe 400mm? I intend to put a membrane down to help minimise pumping with the clay.

[lutonlagerlout]

the most important thing is to compact the sub base in 75mm layers
2@75mm really well wacked down
LLL

[Tony McC]

It depends on the sub-grade but, in most cases, 150mm as 2 layers @ 75mm is adequate for driveways carrying the likes of Tranny vans.