Foundation for large standing stone

[lahauteur]

Hi, I have read the advice on here many times but not had to ask a question before, I can't find an answer to this one.

I have a large granite stone, 6'6" about 2.5 tonnes that I want to stand on my lawn. It is firm level ground, slightly clay type soil. I don't want to bury the stone and don't want any plinth showing. The stone has a hole and I will use a 500mm 1" stainless bar to pin it to the slab. What sort of foundation would you do?

Thanks.

 

[Thermo]

what is the cross sectional size?

 

[lahauteur]

It is roughly 2x3'

 

[Thermo]

then youre looking at having the slab hidden, with the bar coming up through the lawn for it to sit on. If the ground is solid then i would treat it as a glorifed fence post foundation. Dig a hole about 2-3 feet deep and backfill with wet concrete around the supporting rod. The ground will take the weight of the stone, you just want the safety factor of the rock not falling, so a deep slender hole will stop any leverage of the bar. Quite often these things are installed simply sitting on the soil, with no support.

 

[lahauteur]

Thanks,
I was thinking about two foot deep, I will go a bit further. I am planning on leaving a well in the top that I will fill with concrete just before I lift the stone so that I can tip the stone upright with the rod already in it. Not sure if this will work as I will unable to get to it to tamp it down. Will I need to?

 

[Thermo]

i would think that will be fine. have fun lifting it!