Densification of shallow sandy pile footing by 'throwing stones in it'

[Greenalleycat]

Hey all,

I'm working on a job in construction at the moment
The design is for 375x375mm or 500x500mm shallow (400mm deep) pile footings to bear on clean sands to support a timber subfloor above - pretty normal
The design bearing given by the geotech was relatively low, hence the large footings, but they have undertaken some confirmation testing during construction and have concluded that the ground bearing is even lower still in some areas
They have now come back to me with the recommendation of throwing some ballast stones in the base of the posthole footings to densify the material prior to pouring the concrete footings
I asked if these needed to be compacted (and how we would actually achieve that practically) but was told that no compaction was necessary - we just needed to throw them in
I don't really understand this - putting some large stones in and compacting it to take out the surface softness and provide a firmer base makes perfect sense...but just throwing them in with no compaction??
Has anyone ever had a similar recommendation - is there any science or sense to this?

P.s. - I only want a discussion on this stone-throwing recommendation, not on other aspects to consider
I do a lot of geotech testing myself and have already raised a number of other points with the geotech for discussion

 

[jayrod12]

I've never heard of that and can't understand what benefit it would provide.

And those aren't big footings where I come from. Where I am, if it isn't 750x750 we don't even call it a foundation.

 

[Greenalleycat]

These are pile footings under a load-bearing hallway wall in a single-storey house - is that the context you're thinking in?

I am rolling with the assumption that the geotech I was talking to was the middle man between me and his boss, and something got lost in translation...otherwise this does not make sense to me

 

[wrantler]

Dropping the stones from an excavator bucket 5' above the hole = compaction

Now that is out of the way. I always wonder how you compact sand...I have never seen it work in field. Am I missing something here?