How high for sub base material? - Drive extension

[Bobbyboy]

Ok, I am getting 3 tons of grade 1 sub base material (limestone) delivered next week, so that I can finish my drive extension.
My question is, if the recommended depth of the sub base is say 120mm,tamped down, and I then want build that up with say gravel to ground level, ie existing drive level. with 35/40 mm of gravel, how much below drive level should I fill in with sub base material to tamp down so that it finishes at the required level?

Should I go for 150mm of sub base and tamp down to 120mm or what??

Thanks

[alan ditchfield]

120mm of sub base will compact to roughly 95-100mm depending on how wet the material is.

[Tony McC]

It's not just moisture content, but type of aggregate (limestone/gritsone/crushed concrete/granite??) and efficiency of compaction equipment. The only way to be sure just what depth of uncompacted material is required to give a pre-determined compacted thickness is trial and error on site. You might find that 150mm will compact down to 100mm, but then it might go down all the way to 80mm, or as little as 120mm.

This is the reason why I don't give data on the main website about just how much sand or DTp 1 or Crusher Run is needed to give such-and-such a depth. I just don't have the time or the inclination to list all the possibilities!

[alan ditchfield]

Tony is right as usual that you cannot accurately predict how much the sub base will compact, but you say you are using limestone i assume is 40mm to dust, and in my experience 5 inch will compact by nearly 1 inch as a ball park figure.

[Bobbyboy]

Ok thanks Tony and Alan. I guess I will have to just play it by ear then.
It is limestone , 40mm down to dust, I am using.
Err, so will that make my calculations of how much I need redundant then? 100mm times 10.5 meter sqd = 1.05 meter cu times 1.9 = 1.995 or 2 tons now.
The 100 mm sub base will go ontop of broken/smashed concrete of about 40/50mm thick

Thanks

[alan ditchfield]

Stay with your original calculations it is easier to get in a little extra sub base than it is to get rid of surplus, plus these calculations are only as good as the bm that you are using. :rock: