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gravel under slab on grade

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I have a situation where I have specified a 5" reinforced residential
garage slab over 2 inches clean sand, 6 mil vapor barrier and 4" crushed
aggregate. As it turns out the existing subgrade is sand, probably dune
sand from the area that was brought in as fill 100 years ago. The sand is
fairly clean, very deep and appears cohesionless. The contractor wants to
pour the slab without the gravel base. He wants to moisture condition the
existing sand and compact it with a light roller, then place the V.B.
directly over the sand and place the 2" sand cushion over the V.B.

He believes the gravel is not necessary due to the existing sand subgrade.
We all know he simply wants to save money, but is the gravel omission
justified. Any thoughts on this?


Jeff Smith. S.E.
phone: (415) 543-8651
fax: (415) 543-8679
email: smthengr(--nospam--at)

Smith Engineering
27 South Park
San Francisco, CA 94107