The order, MOT before or after screw piles?

[Dreadnaught]

Question: lay the MOT layer before or after the piles?

 

My build is finally getting going on-site. I have signed-up for building control and my ground workers will be excavating for the levels this week, with lots of muck-away (10x grab lorries for soils are mentioned).

 

Next will be screw-pile installation. 26x screw piles and the installer is booked for two weeks time.

 

The installer is adamant that service trenches (foul drains, electricty duct, and water main pipe, etc., all under the raft) should go in AFTER the piles.

 

Then after that, my raft foundation requires 100mm of well compacted MOT Type 3 and 30-50mm of sand blinding. 

 

Do I lay the MOT layer before or after the piles? If before, it provides a good base for the pile installer, but the soil is already quite good and gravel-ly for the digger with its torque head. If before, the MOT will then be messed up by digging the trenches for the services.

 

Anyone else have any relevant experience? What order did you follow?

[Mr Punter]

If the piling rig is OK on your existing ground and that is confirmed by the contractor, do piling, then services then MOT / sand.

 

Sometimes the bigger piling rigs need loads of ground preparation.

[Dreadnaught]

Thanks @Mr Punter.

 

7 minutes ago, Mr Punter said:

If the piling rig is OK on your existing ground and that is confirmed by the contractor,

 

Yes, I sent the installer a photo of the exposed ground surface and he seemed happy.

 

A concern about doing the MOT layer after the piles is whether it will be easy to spread it, presumably using a mini digger, and run the plate compactor around the 26x screw piles. Any relevant experience?

Edited November 2, 2020 by Dreadnaught

[Jilly]

Just had this done for the mini piles on our extension. We are on clay/tree roots. The piling contractor asked my builder for a level surface compacted with MOT.

 

'That looks a bit high', I muse. 'Nah, it's fine'. 

 

 The pile people made the builder come back and dig more out...or threatened to charge him, I think.  I was very glad the builder was sub contracting the pile people... 

[Mr Punter]

If you lay MOT first you will need to sacrifice a fair bit as it will be contaminated when you dig your trenches and even a bit when they install the piles. 

[Russell griffiths]

You can stick a truck load down if you want to avoid them dragging mud out onto the road, but it will be sacrificial and get messed up and will need another load on top for correct levelling.