Fill volume estimate accounts for compaction?
Fill volume estimate accounts for compaction?
(OP)
I have been given a fill estimate for a project that exactly match the estimates for volume from excavation to grade. My question is, shouldn't this volume be increaced to account for compaction? Last I heard, volumes of fill sold by a pit was calculated using yards hauled in a truck-loose. This doesn't seem to account for the at least 20% decreace in size from the stockpile subgrade...





RE: Fill volume estimate accounts for compaction?
How were the estimates given? If by weight, such as tonnes, then there should not be any losses, provided that the compacted density is used rather than a fluffy density.
In my days as a Public Works manager, I insisted on payment quantities be by weight. You see, prior to that, the auditors always seemed agitated at the fact that we could never balance the hauled yardage versus stockpiled yardage. When we went to a loader scale, and weighed all materials, the problem was solved.
As proof, I have over three years of gravel and coldmix hauling data. We used a 5.0 yard (heaped) loader bucket. Now the loader could load a 20 yard buggy with three scoops and the total average weight was 25 tonnes. In the truck the density of the material was 1.24 tonnes/yard. In the loader bucket those same 25 tonnes had a density of about 1.7 tonnes/yard. See how things can quickly cost more money if a volume calculation is used? To answer your question, the "fluff" factor should be used in the trucks, if that is the yardstick, however if the loader bucket is used a different "fluff" factor should be applied.
KRS Services
www.krs-services.com
RE: Fill volume estimate accounts for compaction?
RE: Fill volume estimate accounts for compaction?
RE: Fill volume estimate accounts for compaction?
If you are buying borrow from a pit, then be sure everyone is clear on what you are paying for as quantities. If your plans are calculated for compacted yards and your contractor is counting truck loads for yardage, you can be paying 30% to much because the loose yardage in the trucks is much greater than the compacted yardage in place
RE: Fill volume estimate accounts for compaction?
I have found that if I know what my placed quantities are, including compacted densities, I specify the fill to be paid by weight. The rational is that a tonne, is a tonne, is a tonne, no matter how it is loaded, fluffed or compacted. Load with a loader scale and include a clause for disputes over calibration....I will provide more detail if required (but I have yet to have a contractor dispute the scale).
KRS Services
www.krs-services.com
RE: Fill volume estimate accounts for compaction?
We ended up estimating by volume using a "fluff factor" of 20%.
I had the idea afterward thinking it through, and reading this forum, that estimating by weight would have been useful, and maybe more accurate. This would involve taking the total volume, which I think was 7,000,000cf, and translating to tons using a Proctor Value for unit weight.
7,000,000cf x 135pcf = 94.5 lb6 (or 473000 tons)
This way, you'll have the final weight predicted using the value of compacted material! True, the fill probably won't be placed at 100% compaction, so you may have a slight overestimate, hopefully not by much if they're doing a good job of compaction. lol
It's also true that neither method accounts for settlement! This estimate was given off the cuff, still I wonder if this is a glimpse of the genesis of budget overruns....
Great input. Enjoy the weekend.
RE: Fill volume estimate accounts for compaction?
RE: Fill volume estimate accounts for compaction?
The estimate is for dirt. The estimate was acually given by the cubic yard. I'm just saying I would prefer the weight estimate conceptually if the quarry were able to give a cost estimate by weight. It seems to me weight would be easier to estimate using the compacted unit weight you get with a proctor value. I believe also that truck tickets usually report tonnage and not yardage, like, say, concrete truck tickets. Also, if you estimate by weight, you don't have to use an arbitrary fluff factor that might vary as to whether you were using sand or a well-graded pit run. This leaves variables in settlement and/or original volume estimates.
Anyway, this is all speculated. If I knew the convention, I wouldn't be asking the question. Thanks again.
RE: Fill volume estimate accounts for compaction?
RE: Fill volume estimate accounts for compaction?
Wolfhnd, I understand your reply, but I must disagree. I've had to excavate, waste and otherwise move way too much material in my time. In most cases you are wuite correct, the m3, or m2 as measured is fine as a payment concept. However, when hauling borrow or import, if the cross section methos is not accepted or implemented then to pay by measured truck is kind of a waste of money. I suppose moisture content with respect to measured tonnage will have an effect to some extent, but experienced judgement dictates that the MC in stockpiles of material do not vary that much, but shrinkage rates do! In Alberta, municipalities are subjected to asset audits every year, this includes stockpiles of aggregates and "valued" dirt. Stockpiled and hauled values have to be accurately accounted for and when determining quantities by the truckbox method and measured methods, the values could never, ever, balance reasonably, even with shrinkage rates. Now, when I changed to measured weights (tonnage) factoring in MC, I had balance. Furthermore, government contruction contracts now preference asphalt and aggregate to be measured by the hauled tonne, or placed volume....never by the box count. Shrinkage factors are too open to dispute and opinion.
KRS Services
www.krs-services.com
RE: Fill volume estimate accounts for compaction?
RE: Fill volume estimate accounts for compaction?
R.A. Hassett, P.E.
rah1616@hotmail.com