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To gravel or not to gravel

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Jeff, 
I had the same situation once, and went without gravel.  The only advantage I
had is that the soil engineer ok'd the design without gravel, taking the
issue out of my hands.

A few other comments:
a)  5" is very substantial for a residential slab, so you've got this going
for you.  How may five inch thick res. slab failures are out there?
b)  When they vibraplate the soil, you _can_ walk on it without leaving a
trace (grasshopper....)
 c)  What is the gravel really doing in your situation anyway?  Water will
move through the soil horiz. with or without the gravel, if anything the
voids in the gravel might cause _more_ settlement.  Though I doubt it in
either case.
d)  One reason for the sand over the gravel is to allow shrinkage of the
concrete (floats on the sand), so sand is preferred directly under the slab
anyway.  What's really better about gravel under that sand, then just more
sand?  I think I studied this in Philosphy 101.   NOTE: I'm not suggesting
skipping the visqueen, just the gravel.
e) Can you talk to the concrete provider regarding salt resistant admixtures?
 It'd be best to get the liability for this transferred to them if you could.
f)  I won't comment on whether to allow the contractor to benefit from the
change or not, but if you don''t need gravel, there's no advantage to using
it anyway just to keep the contractor's margin down.  Can you split the
savings with the owner and contractor -- Maybe a three way tie for last?

Brian Veit, P.E., South Lake Tahoe.