Driveways Question

Concrete versus aggregate sub base for a driveway

Hi

I am looking to get a new block paving driveway and am unsure if a granite Type 1 sub base or a lean mix sub base would be best.

The ground is predominantly London Clay (CBR of <5% and I am on the very edge of a possible flood zone) and the two options are:

1 - Type 1 excavated to 210mm
2 - Lean mix excavated to 150mm

With this type of ground is one better than the other?

I look forward to your thoughts

4 Answers

Best Answer

We would always excavate to 8inches depth, lay terram (orsimilar geotextile sheet) then stone up with mot/crushed concrete etc, then sharp sand then the block. I would not advise lean mix ever when using block paving, it goes against the principle advantages of the method by stopping slight movements in the pavoirs. Make sure you consolidate every step with a wacker plate as much as possible and you,ll be fine.

I give a 10yr guarantee on my driveways using this method. Never get tramlines etc.

Good luck
Dan

Answered 30th Apr 2012

Local patios and driveways

Member since 24 Jan 2012

100mm type1 with 100mm leanmix, finish materiel on top. happy digging

Answered 30th Apr 2012

PHOENIX CONSTRUCTION

Member since 21 Nov 2011

Hello
Just to clarify , I take it you are laying block paviors, --- CBR--- is Califonia Bearing Ratio ,[a measure of ground softness] Yours is probably OK if the 210mm is the stone depth . [ you could use a Geotextile and thin the stone ]
The use of lean mix is a way of reducing/ avoiding --- digging out/ cart away / using a decent whacker/ roller, or laying the sub base and sharp sand in the correct layers , or laying 'without' concrete backed up edgings [using screed tubes, and throwing a bit mortar on the edge blocks ].
Also helps avoid digging up shallow laid service pipes and cables ! so it has a few redeaming features.
A block drive is flexible so laying on 'concrete' is against what it is , I have laid bus laybys on bitmac [ base/ binder course ] and 40 n r/ concrete, with 50mm sand -- flexible .
Correctly laid there is nothing wrong with stone and sharp sand .
The depth/ type of subbase is to stop frost heave [ max about 460mm down, in the UK, but depends which part ] so all of the materials need to be frost free [ recycled agg is no good if it has mortar or brick in it !] Only quarried type 1 is frost free [ or clean concrete recycled]
If you have a high water table , in winter with a heavy frost , you need the correct depth of constuction to help stop heave .

Problem with all of the above is the cost, on a relaid domestic driveway job , the lean concrete base [ truck mixed] is cheaper/ faster , and probably OK if the edges are laid properly .
There is also the issue of planning permission / sustainable drainage to think about .
Cheers
Peter



Answered 30th Apr 2012

Beamish Construction Services

Member since 4 Nov 2010

I would use MOT for block paving normally but in your case this may not be possible because you are on a possible flood risk zone. I would recommend using a good geo matting to start. On top of this you may have to use a good washed sub base. Normal sub base will not allow water drain through. This should be laid as normal with 2 times 125mm layers compacted down to create a 200mm base. It may be necessary to use specialist netting to provide extra stability in the sub-base. Over this you should lay a fine washed gravel normal 5mm, not sharp sand, on a second layer of geo matting compacted to a thickness of 50mm. The blocks should be a block made for flood risk zones which have larger lugs on the sides. The blocks should then be brushed in with fine gravel and compacted as normal. It would be necessary to curb the sides of the paved area to help contain the paving. It may also be necessary to lay field drainage below your drive in a geo- matting protected trench filled with washed stone. It also wise to wrap the field drain in a permeable membrane to prevent silting up of the drain. The drain should be connected into the surface water sewer, not the foul water sewer. I would check the regulations for your location because you may need planning permission to put in a drive/new drive and there could be restrictions on how it must be done.

Hope this helpful
Dan

Answered 27th Jul 2014

Daniel Tibbles

Member since 9 Jul 2014

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