Fill volume estimate accounts for compaction?

[dirtsqueezer]

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...

 

[KRSServices]

Dirtsqueezer,

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

http://www.krs-services.com

 

[dirtsqueezer]

Ok. That solves the problem. The compacted weight of the material as reported by the gravel pit is 135pcf. This can in turn be used with the estimated volume of the fill to return a total estimated weight. Thanks for the help.

 

[wolfhnd]

We always use the compation rates furnished by our geologist,even so you can often have unknown conditions that affect the final volume. One of common problem is settling of the soils under new fills. This can acount for as much change in final quanities as the fluff factor. The fluff factor is not fluff, its the fact that nature has a way of lowering the compactions of soils after they are deposited. When you excavate them and compact to 98% or what ever you actually have a denser final product. I'm sure you know all this so somehow I missed the point .

 

[snafuman]

Usually you would apply a correction to increase the quantity of fill to allow for shrinkage. So if you had a grading plan where the uncorrected cut and fill were equal, you would actually be short of dirt, because of the shrinkage once the fill is compacted.

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

 

[KRSServices]

To resolve these issues, I specify fill volumes by weight, or the tonne. For reasons none other than there is a "ton" of money to be saved, pardon the pun. For example, I for one have kept data whereby a 20 yard wagon, hauling crushed gravel or coldmix, will weigh (on average) 25 tonnes. Yet, the loader (5.5 yard bucket) will load the material in three loads. The reason is because in the bucket, the material is much more dense than in the truck box.

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

http://www.krs-services.com

 

[dirtsqueezer]

Thanks for all the input, guys.
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.

 

[wolfhnd]

I thought we were talking dirt. It does not make since to me to pay for dirt by the ton. All you care about is the embankment height etc. and the compaction. We do alot of embankment inplace jobs leaving the overhaul and compactions rates out of the equation. Asphalt by the ton is fine but what is more important again is the final products density, thickness and mixture not the volume or weight. A good way to handle it is to pay for new pavements by the square yard and resurfacing by the ton. Resurfacing is to hard to calculate in advance due to ruts etc. in the existing surface.

 

[dirtsqueezer]

I'm sorry if I was confusing! I'm obviously not familiar with convention if I'm asking the question, and am operating on a purely conceptual basis here.
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.

 

[wolfhnd]

Moisture content will be too big a factor if you pay by weight, for soil or gravel. Go with cubic yards, meters. Pay for cubic yards of excavation (classified), cubic yards compacting embankment, and overhaul this is the normal convention. Don't sweat the borrow amount that can vary, just make sure you know how much fill you need. There are things to know about how much fill you need, like is there any settlement not related to compaction. You need a good geotech and a lot of luck to get it right so it is best if your contractor can cross section the borrow area after the embankment is in place to pay for an adjusted excavation quanity and overhaul. You also will find some variation in the ground line that you estimated from. Don't worry about it, you can't get the right estimate. Just make sure you get the right final product. I'm in favor letting contracts as embankment inplace, but I'm not in favor of with holding the soil survey. Make sure everyone has the same information before they bid. You may have legal issues anyway, don't worry be happy.

 

[KRSServices]

I love these threads!

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

http://www.krs-services.com

 

[wolfhnd]

I would never pay by measured truck. I'm afraid that most of the contracts I have worked on were large projects in the 100,000 cubic yard or more range. We always use the end area method for measurement. I'm guessing that I don't understand the question .

 

[reddog99o]

You should absolutely take the loss of volume due to compaction into account, or you will get into a quantity problem in the field requiring a change order or something similar. Likewise when excavating something that can be cleanly defined, such as a trench, excavation should be figured "neat line" and the contractor involved should be astute enough to know he is removing and transporting a "loose" quantity and should price accordingly. However, the spec should very clearly delineate this condition. When excavating rock in a trench or similar defined area, the cost of rock excavation should be to "neat-line' including acceptable fill replacement. That fill number will exceed the paid quantity of rock due to the material "swelling" as it is excavated. This is a good one to keep a real close eye on to assure that you don't end up overpaying. This is a constant battle with contractors if the spec. is not cast in stone as to the appropriate requirements. Alternatively, you can use the weight method noted in another response. Word of caution here, watch the slips to make sure they aren't slipping you a few extras. If the unit weight is pretty close to accurate, you'll know if someone is playing games on you. R.A. Hassett, P.E.
rah1616@hotmail.com