existing sub grade

[stevio]

i intend replacing an existing tarmac drive,it is in poor condition and is moderately uneven.the sub grade is extremely clayey which leaves stood water on the lawn after any rain .having dug a hole at the side of the drive i have found-2cm wearing course,6cm base course,10 cm sub base(not sure of standard but looks fine)and finally 30cm of hardcore(some stones 10cm across).this whole lot sits on the clay sub grade.what on earth do i do-rip the lot out?this will cost a fortune to replace but i am willing to if you can advise.will a geo membrane help?

(Edited by stevio at 9:33 pm on June 21, 2004)

[alan ditchfield]

It sounds like you have a 15 inch base there if i was you i would remove what you need to to give you the required level for the new laying course and then re- compact what is left before laying the new surface.

[84-1093879891]

Yeah, I think what you have sounds fine for a residential driveway. It might need the sub-base regulating, which means filling in any low spots and knocking the top off any high spots, as well as possibly blinding over it with a sprinklling of new sub-base material, DTp1 or similar.

What are you using to replace the bitmac? Block paving? If so, stripping off the 80mm of bitmac and tidying up the sub-base should give you a good level to start paving. Using a 50mm block with a 40mm bed gives you 90mm, just 10mm above existing, which is nowt, in driveway terms.

[stevio]

Bit of a glaring omission,yes i intend to block pave.i am relieved to read that i can keep the hardcore.Would you go with a geo membrane?i realise it means reinstating the sub base.At this point i wish to thank you for your time and trouble-your site is almost a public service,congratulations.

[alan ditchfield]

Personally i would not use a membrane as this would involve a lot of extra work for no gain i would simply remove the required amount leave what is left as undisturbed as poss, level and compact, then lay the new surface.

[84-1093879891]

Forget the membrane - if you wanted to install one, it should go between the sub-grade and the sub-base, which would mean digging out all that existing material, just to put it back.

Waste of time - forget the membrane!