Stipping Topsoil and placing Topsoil loss factor

[DHF]

We have a site that has required the contractor to strip and stockpile the top foot of soil after clearing and grubbing has been completed. This topsoil was to be saved for re-use as topsoil after subgrading operations were completed. After subgrading was completed the contractor placed the topsoil from the stockpile into the landscaped area at the same depth of 1 foot with a required compaction of between 85% and 90%. The area of stripping vs the area of placing topsoil is the same. However there was a need to import a significant amount of topsoil. (like half of the stockpile) within the same amount of area. I have heard of shrinkage from bank volume to compacted place yards but not that high. The soil type is a clay loam. Does anyone have shrinkage factors for this type of situation. I have gone through almost 30 pages of interesting threads regarding shrinkage and cut and fill calcs but they don't speicifically deal with soley topsoil and the fact the compaction requirements of topsoil placement is less. We figured about 20% shrinkage which seems to be reasonable. Thank You DHF

 

[VAD]

There are always issues with topsoil quantities. Very often the depth of topsoil is estimated and very often this leads to erroneous quantities. How did you obtain your topsoil thickness?. How did you pay for topsoil removal? The reason I ask these questions is because topsoil quantities are often contentious and measurement in stockpile not very accurate, the same is the case if you took an estimate of depth. Did you survey area before and after stripping and determine volume of stockpile?. If you used area calculations then perhaps your depth of 1 ft was inaccurate either before or after.

Regarding shrinkage, I can vaguely remember about 15%.

I am not sure if I have provided you with the answers you need. What I know that this item has always given problems and answers are not easy unless one has monitored the site during the operations.


Regards

 

[DHF]

VAD: In answer to your questions:

1. The topsoil thickness was specified for both stripping and placing at 12".
2. We paid for topsoil stripping as part of the lump sum item for earthwork and we can determine the area from where it was stripped because that was specified as well.
3. I don't think we did survey the areas after it was strippped.

Thank you for responding. Lets see what others have to say about the shrinkage. Oh by the way the compaction requirement on the placed topsoil is 85% max and not between 85 and 80 as I stated before.

 

[BigH]

VAD is correct - topsoil removal is a contentious issue. You've indicated that the topsoil thickness was "specified" at 12 inches; this does not ensure that 12 inches were removed. Same as the area - without survey confirmation, you have little validity on the quantities involved. I would think that the topsoil is quite "loose" in the natural state and that on replacement and recompaction, I would anticipate more than the 15% VAD quoted - but as a WAG, I might suggest up to 25% or more might be appropriate - this assumes that the clayey loam was not "heavy clay". I also doubt that the topsoil was really 12 inches thick - this seems very thick to me - but hopefully you have a geotechnical report to say that that was the depth of the topsoil.
Advice: during any soil investigation - that a few hand dug holes be dug to get a better idea of actual thickness of topsoil rather than "measure" the thickness in the spoon. I learned this from someone that had been once burned and decided I'd rather not be.

 

[Dirtmaster]

I totally agree with BigH.

If no moitoring of the topsoil stripping was done,

then you can not be sure that 12" of soil was striped.

Shrinkage (in my opinion) does not enter into the equation

since the topsoil should not be be densly compacted.

Also, I cannot picture a site where all of the stripped
soil (@12") would be respread (@12") unless the site had
no buildings or parking areas.

My thoughts are that much less than 12" were stripped

 

[BigH]

DHF - ran across a site the other day while searching for something else. They had two pages of shrink/swell factors for various geological materials.

http://www.cee.mtu.edu/~balkire/ce3401tc/Design Manual/chap6geo.pdf

Hope that works - I hadn't written it down before downloading but got the url off my Download Accelerator. If not try to find me.

 

[ALBUD1962]

Not sure why you would be compacting topsoil as this wouldnot be very beneficial for turf establishment. Usually a respread of 4 to 6 inches is sufficient. I have had problems with topsoil respreads of 12" especially on steep slopes.

 

[francesca]

I work in residential subdivisions in an area where topsoil can vary from 6" to 18". We do not do geotechnical investigations prior to design, and our dirt work calculations frequently aren't worth the paper they're printed on.

Regardless of the depth of topsoil prior to construction, we only require that 6" be replaced. This often leaves us with upwards of 10,000 cubic yards of topsoil to remove from a 30 acre site. It could be that we specify only 6" of topsoil replacement because we want to ensure that our building pads are adequately compacted.

 

[DRC1]

I can see 50% under run. First If the topsoil was not 12 i. thick it as not strpped. Possibly the topsoil was 12 in. thick and was not stripped. Wih out verification, itis difficult to compute not oly the actual topsoil, but also the earthwork quantities. Topsoil is usually fairly loose.
To compact to 90% (I assume modifed) for 12 inches seems to be a waste of good material. If in its natural state it is at 70% (and it depends a great deal on site specific conditions), to go to 90% is a 28% increase. the other factor that has not been considerered is loss. When ever you move material to a stockpile and back, there is loss. Typically I use a factor of 10 to 15%. Therefore you have say 30% shrinkage and 15% loss gives you 45%.
The question is so you are 6" low with the topsoil, do you really need to import more, or by a little judicious regrading, can you utilize the material on site? The six inches is ok for grass, so I would see if you really needed the add'l topsoil

 

[cvg]

I agree with DRC1 as I usually specify 80% min compaction for topsoil and rarely strip more than 6 inches. 90% is too high for topsoil and may actually hinder your revegetation efforts unless you plan to disk or aerate the soil prior to replanting.