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# calculating riprap yield

## calculating riprap yield

(OP)
I am trying to estimate how many tons of riprap per neat cubic yard of placement.  I am thinking along these lines:

1) Determine riprap density from source...assume 155 lbs/ft3 in this case.  That's about 2.09 tons/cy of 'rock'

2) Now the part I need someones experience on is how much void to factor in.  If voids account for 33% of the total volume then this reduces to 1.5 tons per 'neat' cy.  I realize this can vary, but what we have to use something.  I think the void ratio would also vary by what size of riprap is being placed. What void ratio would you use for the
a) 1/4 ton riprap
b) 1 ton riprap
c) 3 ton riprap
d) 6 ton riprap

3) I would also use this information to determine the quantity of concrete used to fill the voids if placing concreted riprap.

### RE: calculating riprap yield

I use 165 lb/cf, 155 is fine.

The void ratio depends on the shape of the object and adjacent objects, not the size of them, provided they are similar...round 6" stone would have the same proportion of space between them as round 12", etc.

For irregular (quarried, ripped or blasted) stone, I use 40% void space, and that is so typically used that I have never bothered to reference a source.  I've seen 35% frequently also, so 33% should be conserative enough for tonnage, while not underestimating the concrete.

Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve

### RE: calculating riprap yield

A common spec requirement is for the stone to have a minimum specific gravity.

"In addition to the requirements of section 703.1, stone for riprap shall have a minimum apparent specific gravity of 2.4 per ASTM C-127"

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