Hi everyone, seems like a pretty professional forum with real facts and no nonesense advice, so would like to hear the views in my particular case:-
I'm replacing a very rough concrete driveway to my 1860 farm workers cottage and although I'd love to to lay real brick or old salvaged brick paviers my wife and I simply cannot afford this (our finances are tenuous to say the least after going bust nine years ago, house repossession, the lot), thus I have to lay the cheapest possible driveway and do all the work by hand including sledge hammering the existing concrete, however I want the work to be quality even though cheap in cost.
I have an old Ifor Williams 2.2 ton plant trailer which acts as a skip and a nearby council recycling centre for dumping all my rubble for free and for collecting bulk materials at the best rates.
Having read the info in pavingexpert.com on the various ways of laying driveways one thing stands out as being of ultimate importance, the need for a suitable sub-base, in fact the advice goes so far as to say that if someone says a new sub-base is not needed then show them the door! I believe that in my case with the type of sand/silt alluvial deposit in this area I actually don't need one, see http://www.yorkarchaeology.co.uk/valeleaflet-web.pdf (my guess is approx 95% sand, 5% clay and organic matter).
The evidence for this comes from simply walking on the 'soil' after clearing tons of rubble, old bikes, tin cans etc. buried in the garden which as far as I can determine has not been cultivated for 30 years, and being forced to hire a mini digger to losen the rock hard 'soil' down to a depth of three feet. After the final levelling and initial compacting the soil became incredibly firm again unlike any top soil I've ever experieced. Further more, my house is resting on the typical Victorian 'pyramid' brick foundation with the bottom row of bricks at a mere two feet depth laid on top of the soil and after 150 years there has been no detectible subsidence.
Can I therefore get away with laying a new sub-base or will I be "shown the door".
Here are photos (if image download works) of part of the drive starting with heaps of loose soil, initial levelling by eye, firming by treading only, then driving car and trailer over to show how firm this base is.
The decision is yours - if you think the sub-grade is sufficiently firm (and if it's 95% sand, that shouldn't be a problem) then ditch the sub-base. However, I'd be concerned about the gravel top dressing being driven into that sub-grade as soon as you start to use the surface.
The obvious answer to that particular problem would be to use a geo-textile separation membrane, but, as mentioned on the main website, when used beneath just 30-40mm of gravel, they have a nasty tendency to become exposed, totally ruining the look you're trying to achieve.
So, even though there might not be a structural need for a sub-base, I'd still be tempted to use one, albeit a minimal 50-75mm depth, on aesthetic grounds. Then, if the gravel surface is scuffed, it's a very similar looking sub-base that's revealed, and not some glaring light-grey sheet of polypropylene fibres. You could, of course, use a sep membrane between sub-base and sub-grade, if you wished, but that could well be a bit too "belt and braces", even for me!
Thanks Tony McC, I can see your point on the gravel being driven into the sub-base, I wonder, is there a point of saturation when the gravel stops being driven down? Alternatively I could scrape off an inch or so and increase the depth of gravel coupled with 'topping up' occasionally.
Anyway you've put my mind at rest about not laying a dedicated sub-base, thanks a lot.
There is a point where the garvel is no longer lost to the sub-grade, but there's no way of determining in advance just when that point might be reached. It you be next week, next year or next decade.
Increasing the depth of gravel is fraught with difficulties because any depth greater than around thrice the max size of the gravel turns it into a gravel trap rather than a usuable surface. So, if you're using a 10mm gravel, 30mm is roughly the max usuable depth; for a 14mm gravel, that could be 42mm, etc, etc.
Base you are showing may look and feel ok now, but once it gets wet in the rain, think you will be in trouble with it padding up as you drive on it.
As Tony says its up to you, but think a base layer would be a worthwhile investment for the furture, save on gravel anyway so may even work out as cheap.
Good point Tony McC, didn't consider that increasing the depth would turn it into a gravel trap, pretty obvious when you think about it, hey ho, back to the drawing board!
Anyway, now that I'm breaking up the old concrete driveway (the photos were of the old tarmac-ed garage base), I'm finding quite a good layer of small whitish hardcore so with any luck I might be able to use it here at least. I'll send another photo in a couple of days of this hardcore to see what you think.
Hi ABILITY,
Thanks for your comment but this 'soil' really is stable even when flooded, and of course being approx 95% sand the water drains away PDQ so any tendancy to muddy-up quickly disappears with the water. This though is only on the short term, you may be right in the long term so have taken the advice I've received and will lay a sub-base were it's required, thanks to all.
