How big a Bomag?!

[willbish]

My cautious ground investigation stipulates a 10 tonne static roller be used for compaction...

 

I've just been looking through the hire catalogue and 100kN of force is a LOT bigger than I was expecting. So much so that I don't think it would be possible to get such a machine down to the required level without a crane/large hiab.

 

An 80kN model doesn't reduce the size much. Can I compromise further without jeopardising the integrity of my foundations?

Many people who have been to site, including a surveyor commented that the ground is excellent. Large fragmented stone, no organic matter. A ground worker who came to quote said he thought I could build straight off of it.

 

What size machines have others used to compact the type1 on their rafts?

 

 

 

[vivienz]

This is what the MBC guys used to compact the hardcore for my foundation.  On the right, in case you're blinded by the rubble.

[willbish]

@vivienz I'd say that's about 40kN model

 

 

[PeterW]

Are you sure your engineer has got his calculations correct ..??! That’s major road territory and your ground bearing is nowhere near that is it ..??

[willbish]

@PeterW that extract comes from the Ground Investigation report, the Structural Engineer is following it to the letter. I'm inclined to think he is being overly cautious  (again) rather than incorrect. His 50kN/m2 ground bearing figure has been remarked as surprisingly low

[PeterW]

@JSHarris what was your ground bearing overall ..?? 50kN/m2 isn’t a lot but trying to    figure out how they have come to that sort of compaction level 

 

[Jeremy Harris]

16 minutes ago, PeterW said:

@JSHarris what was your ground bearing overall ..?? 50kN/m2 isn’t a lot but trying to    figure out how they have come to that sort of compaction level 

 

 

There's a post here somewhere where I calculated it, remembering to allow for the 45 deg outward spreading zone, that increases the effective bearing area.  Off the top of my head I thing the total house bearing load on the ground was somewhere between 2 and 5 kN/m²

[willbish]

6 minutes ago, JSHarris said:

the total house bearing load on the ground was somewhere between 2 and 5 kN/m²

Ah yes I do remember reading that in one of your posts @JSHarris Considering my building is of a heavier construction to yours (ICF) and a full two storey, I could assume twice the ground bearing of 20kN/m2

 

Me thinks a 40kN roller will be on hire next week...

[Jeremy Harris]

You can work out the sums very roughly.  Take the area of the ground floor, multiply it by a given ground bearing load in kN/m² and then divide the answer by 9.82 and that gives you the total weight of the house, but you have to factor in a reasonable margin for safety (typically a number between 2 and 3 I think - I don't have the relevant Eurocode to hand to say what the margin is for a load bearing slab foundation, but doubt it would be higher than 3).

 

Say you had a ground floor load bearing slab area of 100m² and you are working to a margin of 3 and your ground has been compacted and tested to a max allowable bearing load of 40kN/m² .  100m²  x 40 kN/m²  = 4000 kN  max allowable load, divide that by 3 (the margin) and you get a max allowable total ground bearing load of 1,333 kN.  Divide this by 9.82 and that gives the max allowable weight of the house, including all dead and live loads, of 135 tonnes.

 

Our 130m² one and a half storey timber frame house, with pretty heavy cellulose insulation, weighs around 40 tonnes.  If it was block and brick construction it might be something like 50% to 70% heavier.

 

Hopefully you can do some rough sums and see what sort of load your house is likely to put on the ground.  Remember to allow a reasonable margin, say 2 or 3, just for safety.