Building driveway on heavy clay soil

[dunny]

Morning all.

I tried searching the forum for an answer to this one but had no luck.

I want to put a fairly large hammer head drive in next to my house;it will ultimately lead up to a new garage. It will most likely be a gravel drive and due to the levels involved it will be on a shallow(ish) incline.

All the land around my property is quite boggy and is basically soil on top of clay, consequently it doesn't drain very well. In the area of the drive I have previously dug down for a land drain and the soil goes down around 12 -18 inches before hitting soft clay.

Given these circumstances what would be the best way to approach laying a solid drive? I have read about stabilising clay with lime but not sure whether this is required?

Am I best digging down to the clay layer (which could be over 2 feet down at the top end) or just taking off the top soil as normal?

What base would be best; crush and run?

To ensure the edges don't start to collapse do I need some sort of retaining wall (maybe concrete block laid flat? If so, laid on the clay or just compacted topsoil?

Sorry for all of the questions however despite the fact I have done a few drives over the years I am concerned about the boggy nature of the land and the clay base.

Thanks

D

 

[John D v2.0]

I'd have thought once you removed all the top soil and roots etc down to the sub soil and get 100+ mm of well compacted hardcore, it doesn't matter how soft the underneath is. As long as the ground level isn't dropping away and sliding.
However depend why it's wet, if you have a spring underneath even reinforced concrete won't stay still!
Paving expert is a good resource if it covers your situation though, although you've probably already seen it.

 

[dunny]

Thanks John.

It is wet due to the run off from the land behind. I have improved it with a land drain but it is still very soft and boggy.

My thought were to dig out maybe 300mm and then do 2 layers of compacted brick / stone and then 100mm gravel. Hopefully this would also act as a bit of a soakaway too?

D

 

[^woody^]

And a geotextile reinforcing mat to stop rutting and prevent wet clay rising. I'm not sure if it goes on the clay before the hardcore or in the hardcore.

Otherwise yes, just scraping the topsoil should do.

 

[stuart45]

On top of the clay to stop it mixing with the hardcore/Mot.

 

[noseall]

On top of the clay to stop it mixing with the hardcore/Mot.

Correct.

 

[John D v2.0]

Correct indeed but if you're using proper MOT it is supposed to have the right blend of sizes to prevent this pumping of wet material upwards. That is assuming it's compacted correctly and not improperly handled to separate out.

 

[noseall]

Correct indeed but if you're using proper MOT it is supposed to have the right blend of sizes to prevent this pumping of wet material upwards. That is assuming it's compacted correctly and not improperly handled to separate out.

If you ask for MOT type 1 you are going to get a 40mm - dust mix of stone and finer material. If you were serious about combatting a poor substrate you would need to order two separate loads of gear - a larger grade of stone first (compacted) and than the MOT type 1 etc.

 

[John D v2.0]

thanks for the explanation. I was lead to believe the dust was designed to fill the gaps so the clay couldn't move upwards, but I didn't look too much as our subsoil was not sodden. I think the M.O.T. themselves (ie road builders) probably use a lot more than a single layer of anything!