Excavation levels on clay ground

[New to this]

Hoping you experienced folk will guide me; how do I research / know what is the 'correct' ground prep for excavating - in this case specifically site access (needs widening considerably as all construction vehicles need to get from single track lane onto site currently entrance <10m wide) and then the 30+m of sub base that will eventually be finished as our new driveway and also the 2m perimeter around the house for scaffolding, and later for pathways?

 

I haven't chosen a final drive surface yet.

 

Two builders have given figures but I can't compare them as one goes down 300mm while the other 400mm (this is to lay geotextile, then hardcore, then Type 1 compacted, in case that makes any difference).  I want to spend the 'most minimum' I can on this without compromising quality; it needs to last once driveway is topped with whatever the final finish is, but I don't want to throw money I don't need at it either.  Ground is very high plasticity clay, if that makes any difference. 

[SimonD]

2 hours ago, New to this said:

Type 1 compacted, i

 

I'm not an expert of ground works but my understanding is that new driveway surfaces need to be permeable which means Type 3 not type 1. With our groundworks company for driveway prep, they specified a compacted finished depth of 200mm of hardcore (type 3) and we are on clay soil.

[FarmerN]

If you have a suitable outlet pipe or ditch put a land drain or two in before any fill, to take as much water away as possible during and after build.

We were lucky having a suitable ditch along side site to drain into.

We put two land drains in just beneath surface, covered with membrane then permeable stone                  ( screened crushed concrete) If lorries are running on this go for as deep as possible, and if possible constantly fill any soft spots where traffic causes ruts. At the end of the build the surface of this was loosened, stone recovered from around site, as much as possible, while leaving land drains in place, and all used to create a permeable drive way and rear patio area.

Again we were lucky in being able to build site up a bit whilst having good fall for final surface drainage, and sufficient depth for services to go above land drains.

[New to this]

Thanks @SimonD - I didn't know about the Type 1 vs 3 thing. Is that in the BRegs? My site is quite a decent size and there will be about a third of an acre left after build for water to run off to, if that makes sense, but I've no idea about this stuff and it does concern me I'll run into issues with BC inspections and sign-offs! 

[New to this]

On 12/01/2026 at 08:54, FarmerN said:

If you have a suitable outlet pipe or ditch put a land drain or two in before any fill, to take as much water away as possible during and after build.

We were lucky having a suitable ditch along side site to drain into.

We put two land drains in just beneath surface, covered with membrane then permeable stone                  ( screened crushed concrete) If lorries are running on this go for as deep as possible, and if possible constantly fill any soft spots where traffic causes ruts. At the end of the build the surface of this was loosened, stone recovered from around site, as much as possible, while leaving land drains in place, and all used to create a permeable drive way and rear patio area.

Again we were lucky in being able to build site up a bit whilst having good fall for final surface drainage, and sufficient depth for services to go above land drains.

Our perc test failed for soakaways, so our planning has insisted on all surface water being piped into a drain with a rumble strip and then on out to the ditch. Aren't we fortunate?!