Voids in rock stock pile 2

[Snatch]

I am working on an earthworks project and have to come to an agreement with the contractor for the volume of rock (solid boulders) excavated. The contractor has surveyed the rock stock piles using a total station and computed the volume using modeling software. We are reasonable comfortable with the total volumes however we think that there should be a deduction made for voids (air) within the stockpile. We are suggesting a 30% deduction for voids; naturally the contractor is in a disagreement. Has anyone come across any supporting information that determines the amount to be deducted for voids in a stockpile?

Regards,
Snatch

 

[cvg]

Depends a great deal on the shape and uniformity of your rock fragments. Unless you have some unusual minerals in your rock, try a value in the range of 1.5 - 2.0 Mg/m^3 for typical dry density of crushed rock (modified after Hansbo, 1975)

 

[bltseattle]

The measurement method should have been defined in the project specifications. "Neat line" or "measured in place" means the quantity is measured in the ground, in which case the voids in the stockpile would NOT contribute to the volume for which the contractor is paid, and the pile volume would be reduced by the voids. "Haul" or "truck" measured would be after the material is removed, and in that case the contractor should be paid for the volume of the pile, including the voids.

If it is not spelled out in the project specs, see if there are other specs referenced in such as APWA, which may then clarify.

 

[cvg]

If it will be hauled, you can weigh the trucks and then correlate this to the actual specific gravity / density of the rock material and back your way into the in-place volume.

 

[Snatch]

Bltseattle: I argree this should have been established in the contract documents, unfortunately it was not defined properly there.

Cvg: The boulders are already transported/deposited offsite

Rgds
Snatch

 

[GregLocock]

30% is very high. The best that can be achieved with equally sized spheres is 26% voids - and you have unequal sizes, as well as being non spherical, all of which help the packing density.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[PEinc]

According to Illustration 31 on page 58 of Estimating Manual for Hydraulic Excavators (a 1971 Koehring publication):

Rock, blasted: 4000 pcy in bank; 50% swell; 0.67 swell factor; 2680 pcy loose wt.

Shale: 3000 pcy in bank; 33% swell; 0.75 swell factor; 2250 pcy loose

Sandstone: 4100 pcy in bank; 54% swell; 0.65 swell factor; 2700 pcy loose

Swell factor "is a factor to convert loose cubic yard weight to the bank cubic yard weight, and is used by the estimator as he considers both the net volume of pay yards being excavated, and the volume of loose yards which is actually carried in the dipper" (of a hoe bucket).