Service Ducting to/through Raft

[LA3222]

Daft question before I knock it on the head for the night!

 

I need to put down a big pile of stone for my sub base - about 600mm.  Is it easier to lay the duct in at the bottom, running it to where it needs to poke up through the slab and then build up the layers after or get everything wacked flat and then dig it back up to  run the ducting to where it needs to be?

 

On the one hand digging it back up after doesn't feel right - trashing the flattened stone to reflatten it again. 

 

But laying the duct at the bottom to where it needs to be seems to have its problems...namely being accuracy and then having to build the layers up around a load of pipe poking up.

 

My gut says just dig it out after and then re-lay the stone.  I have seen loads of pics which show this is how the foul runs are done, but that's not such an issue as those pipes are towards the top of the stone.

 

Some feedback from those whom have done/seen this carried out would be appreciated.

 

Ta 

[Russell griffiths]

Dig out after, get it nice and flat, then it’s a nice surface to set out on, shallow trench, re level and compact. 

 

Others will I’ll probably say put them in first, but 600mm is a lot of stone, that will put your ducts very deep and may make for some awkward angles coming up through the slab.