BigWallop wrote:

"John Armstrong" wrote in message
...

On 10 Jul 2003 15:09:22 -0700, (Jon Weaver)
wrote:


Currently the trech has been dug out and they have started
constructing the metal work in the toe. The dimensions of the metal
work is 400mm(h)x400mm(d) and the current trench approx 450mm deep.
However, the metal work is placed right on the soil below as no
hardcore has been put in.


When you say right on the soil, do you mean that, or are there
spacers? There should be spacers so when the concrete is poured there
is 50mm of concrete under the reinforcement.
Have never seen hardcore under the foundations. (An a QS though, so
not really qualified :-) )

--
John


Hard core will be used if the ground under the raft is boggy or susceptible
to flooding, and allows water to wash through under the unit without washing
away any of the soil. The raft will then sit on top of the hard core and
not be bonded to it and this will allow the raft to drain surface water
through to the hard core and back in to surrounding ground. A sort of
sub-terrainian colonial drainage system you might say.


---
BigWallop

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Yes. Hardcore isn't just any old muck. It has a definite mechanical
property - two in fact - derving from the trapped air - ability to
drain, and ability to crush ligthly under stress. Limestone is better here.

This menas it bothg stops ptential subsidence from water, and allows a
certain amount of heave to take place...

The oher property is of load spreading. Here the deeper the better.