UKTC Archive

Re: Holes drilled in tarmac under a tree canopy..

Subject: Re: Holes drilled in tarmac under a tree canopy..
From: GILES HILL
Date: Dec 23 2009 10:57:10
Judging by the fact that the groundworker appears to have ignored the approved detail, I'd be concerned about compaction that construction of a standard tarmac surface would cause.

Drilling holes through an impermeable surface won't achieve much, if the soil profile below is basically impermeable - i.e. it has lost its porosity through compaction.

Decompaction, would require the existing surface to be removed, presumably a load bearing system could then be installed beneath the new surfacing?

Speaking of which, does anyone know if any of the load-bearing systems successfully accommodate lateral diffusion - i.e. so gaseous exchange could continue sideways through a suitably detailed edging, if or when the vertical routes become blocked?




----- Original Message ----- From: "Nick Hammick" <Nick.Hammick@xxxxxxx.gov.uk>
To: "UK Tree Care" <uktc@xxxxxx.tree-care.info>
Sent: Wednesday, December 23, 2009 9:27 AM
Subject: RE: Holes drilled in tarmac under a tree canopy..


Hi Richard

For context, what I said was lifted straight from the annotated notes on their plan.

I am guessing they intend it to be/become porous, by virtue of the fact that they plan to pepper it full of holes.....

I am aware of the product known as porous tarmac, but can not vouch that what they have used is this stuff.

They have suggested this spec " as a tried and tested system ", but only after the event of whacking down 'regular' tarmac as the top course, instead of the required resin bonded aggregate.

Thanks to Guy, Rupert & Richard of Dorset for your comments

Nick Hammick
Tree Oficer

-----Original Message-----
From: Richard Bryson [mailto:richard@xxxxxxxxxxxxxx.co.uk]
Sent: 22 December 2009 15:57
To: UK Tree Care
Subject: RE: Holes drilled in tarmac under a tree canopy..


Hi Nick,

Correct me if I'm wrong but you said, 'The intended surface is to be a porous tarmacadam in a large aggregate with a series of holes drilled at 200mm centres'. Why would they be drilling holes in a porous final surfacing? I seem to remember that the drilling at calculated spaces with granular infill was to do with the laying of non porous materials such as concrete.

Have they spoken to Roy at Geosynthetics? he could advise on such matters. I would suggest a Cellweb substructure with porous tarmac or blocks when constructing parking within a RPA.

Happy holidays!



Regards

Richard Bryson

AllAboutTrees Ltd
Arboricultural & Ecological Consulting
Chartered Arboriculturalists & Environmentalists
Unit B10 Durham Dales Centre
Castle Gardens
Stanhope
Co Durham
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-----Original Message-----
From: Nick Hammick [mailto:Nick.Hammick@xxxxxxx.gov.uk]
Sent: 22 December 2009 15:32
To: UK Tree Care
Subject: Holes drilled in tarmac under a tree canopy..

Dear Forum

Further to a drawing received to discharge a specific planning condition, the following detail is given -

The intended surface is to be a porous tarmacadam in a large aggregate with a series of holes drilled at 200mm centres.

Holes to be filled with fine gravel to allow water to pass through and not clog up any other material.

Tarmac to be capped with a resin bound aggregate at 20mm thickness - which is totally porous allowing surface water to percolate through to the drain holes below.

Wall to wall tarmac has been laid here; in mitigation, they have proposed to drill holes at 200mm centres and undertake the above, over an area approximating to 2no car park spaces.

Now, we are fairly o.k with the resin bound element...my concerns are.. the size of the ' fine gravel ' to be used. Too fine and it'll be fines eh!

Also, is it realistic to expect to be able to undertake/achieve these drillings at this density? A calculation for the number of proposed drilling comes out at approx 570 for 2no. spaces @ 4.8m x 2.4m each.......won't it all just crumble to bits?

My instinct is to get the tarmac removed completely, given that resin bound aggregate was originally proposed here, but.....

Your collective wisdoms please and Happy Holidays to all.

Regards........

Nick Hammick
Tree Officer
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