Compaction Factors 2

[BigRick]

When applying compaction factors, which method is correct -multiplication or division? For example, if you had 10,000Cy of compacted fill, how many bank Cys will it take if you use a 15% compaction factor?

10,000CY x 15% = 11,500 CY
or
10,000CY / .85 = 11,764.71 CY

 

[firebird16]

Big Rick,

When earth is excavated from bank conditions or in-situ it swells, and is now in a loose condition. Swelling is usually expressed as a percentage.

After spreading the loose material it is compacted and shrinks. Shrinking is also expressed as a percentage. The amount of shrinkage is proportional to the amount of compactive effort. It is also expressed in a percentage.

As far as I know, you'll have to know both of these to determine loading factors or shrinkage factors or how much bank volume is required to achieve the CCY you are looking for. Perhaps you or someone can enlighten me on the compaction factor.

 

[BigH]

There's been another thread on this in last month. Do a search. KRS was involved in several responses.

 

[BigH]

BigRick - it is in this forum - Earthwork Balance Computations - Subsidence.

 

[jheidt2543]

BigRick,

The difference between the two methods you are asking about is 2.3%. Do you really know the chactoristics of the material that closely? But, to answer your question, I always mutiplied by the compaction factor. However, I think the key is to use a consistant method and then field spot check the quantities periodically to verify it.

 

[KRSServices]

Howdy Folks, just couldn't resist this one!

BigRick, the solution to your question is not in the measurement of the volume, as expressed in cubic yards, rather in it's weight by volume at measurement. I am assuming your measurement and payment in the contract is by area measurement or by volume. The problem lies with the method of measurement in that if the method was by truck box or buggy loads the material is moved in the "fluff" state (it's density much lower) than in-situ or after recompaction. At first glance, if it is possible to measure the material, then that will be your easiest solution because the weight of the material, regardless of compaction effort or state, will never ever change. However, in most earthworks projects utilizing buggies, this method is not too practical and therefore I would propose the following.

1. Get the geotech to provide several test results on the proposed material. They will be able to provide a range of insitu densities from which to work with. These can then be averaged if fairly consistent (and if it is a small area, they likely will be).

2. Next, if possible, weigh the material in a truck box by loader scale or when full by scale. This will give you some idea as to the fluffed weight of the material. It is not likely that there will be a scale nearby for the buggy, but if a loader scale is available, you can weigh that material as the buggy unloads. The point to this exercise is to determine an average "loaded" density of the material. By choice, I scale as much as possible. There is never an issue regarding compaction factors, measurement and payment. Usually, the main issue is an oversight at the design stage and a misapplication or error in applying the wrong compaction factors at the design stage resulting in additional material being borrowed.

3. By comparing the loaded density to the in-situ or the compacted, you will then be able to calculate your "compaction" factor for the materials. Measurement can then take place at your with little worry. Keep in mind that the geotech will have to take samples as the material could change somewhat and pose a slight risk for claim.

I can provide example after example of some of the factors I have derived over the years, and it still comes down to the weight of the material. Don't forget, if you are calculating the compacted density, make sure the material is deemed moist and not the dry density.

KRS Services

http://www.krs-services.com

 

[Zambo]

This is an interesting question and perhaps, as suggested by jheidt2543, a bit academic as the difference is minimal. If buying the material rather than moving around site the costs could be significant and probably best to buy in tonnes (or tons) and then payment by compacted cubic metre (or yard)

If a weighbridge is not available then buying fill does become a problem. What I normally do in this case is set up a truck inspection point and have a guy to level off the load and then use a steel probe to measure the depth, volume is then calculated. Of course then there is a disagreement over compaction during transportation. When using this method I assume 1.5 0r 1.6 tonne per uncompacted cubic meter for the first few days and then get a closer figure after some knowledge of the material has been gained.

Zambo

 

[wolfhnd]

One of the ways to avoid this problem is to pay embankment in place. The density is always specified so there is no quality control issue if the specified material type is used. This also avoids field measurements by cross section of the borrow sites and overhaul calculations.

The only reason I don't like this method is that the owner avoids all responsibility and puts the liability on the contractor for the swell factors etc. When you do this in a contract the contractor has to protect himself with a higher bid. Since you should have more time and expertise, asuming the liability for the calculations is a gamble that should pay off with lower cost over time.

I have always multiplied by the factor in your case 1.15 to determine how much swelled material would be needed. This is also the number that is used for overhaul calculations. I see nothing wrong with multiplying the volume of the borrow pit by .85 allowing for loss that from spillage etc.
That 2.3% would be a nice safety factor.

Be sure that the quanities and methods are clearly shown on the plans so the contractor knows what he is bidding on.

 

[DBNodurf]

The best way to determine the bulking and shrinkage factors is to conduct 3 or 4 in-place density tests in the borrow to estimate an average in-place density, then conduct a standard Proctor and/or modified Proctor test to estimate the target density. The math required to come up with the bulking and shrinkage factors, as well as the overall bulking or shrinkage factor (it can go either way), should be obvious... (and there are references on the calculation technique...)