Solid density 1

[DougHole]

Hi everyone,

What is the difference between solid density, bulk density and maximum dry density?

Some specs require compaction to 80% of solid density. The US seem to like to require 95-100% of the maximum dry density in a compaction spec.

Not sure how/what the solid density compares to this and what it is?

 

[BigH]

Solid density - and I have never seen this used - could be that density taken maximum theoretical density - look it up for concrete - or it could just be what the density would be assuming the whole was purely at the material's specific gravity (perhaps more likely). By using 80%, they are specifying the amount of voids that they would permit.

For soils, I've always dealt with maximum dry density which is the bulk density divided by 1+water content.

 

[Ron]

Agree with BigH that solid density is maximum theoretical density which, for a 1 cubic foot volume would be the specific gravity times the unit weight of water. Assuming a specific gravity of 2.65, that would yield a maximum theoretical density of 165.36 pcf. For a specification of 80 percent of that, you would need an in-place density of 132.29 pcf.....a practical impossibility for most soils! I have not seen that term used in conjunction with a compaction requirement, but then I'm in the US so we use a different requirement as you noted.

Bulk density is a more elusively defined term. One definition, as given by BigH, is the wet unit weight. In that context you could determine the wet bulk density and then as BigH noted, a dry bulk density.

The maximum dry density is determined by a laboratory test known as a moisture-density relationship. It is the peak of a curve developed by compacting in the lab with a repeatable, known energy input done at various moisture contents to develop both the maximum dry density and the optimum moisture content....the moisture content at which the peak of the curve is defined graphically. This test is commonly called a "Proctor Test" or Laboratory Proctor, named for the developer of the test, R.R. Proctor.

I have attached a brief description of using a Proctor Test. A similar description is contained in the textbook "Principles and Practices of Commercial Construction", 9th Edition; Woods, W. Ronald; Andres, Cameron K.; and Smith, Ronald, Prentice-Hall, 2014.....however, that version is copyrighted and cannot be posted here.

 

[Okiryu]

Ron, BigH,

Can "solid density" also be referring to "soil solids particles density" (weight of solids divided by volume of solids)? If so, this value is between 2.6 to 2.7 gr/cm^3 for most of soils.

Here in Japan, this parameter is normally included in typical soil analysis. That's why I recognize that term. However, correct me if I am wrong, but my feeling is that this parameter does not have too much application if comparing to bulk density. For example, I think that one application of "solid density" is when determining the zero-air-void line in the Proctor test. Other than that application, I do not see this parameter to be used too often.

 

[BigH]

Your definition was that of my first thought - "the density would be assuming the whole was purely at the material's specific gravity" . It would not be used in any way for zero air voids as ZAV is using soil particles and all voids are filled with water. (see attached) I do not see any use for "solid density" in geotechnical engineering.

 

[Okiryu]

BigH, sorry I cannot see your attachment. Could you post it again please?

I agree that "solid density" does not have too much application in geotechnical engineering. But I was thinking that you need Gs ("solid density" divided by density of water) in order to get ZAV.
Bottom line, you are right, I do not use " solid density" in any of my calculations. Also this value is normally between 2.6 to 2.7 gr/cm3 independently of the type of soil, so it is no critical to get this value in the lab accurately.

 

[BigH]

Too much "multi-tasking" . . . hope you can read it . . . .

 

[Okiryu]

Thanks BigH...

 

[Ron]

Yes...in each case where "solid density" is referenced, it has to refer to the solid particle portion of a weight(mass)-volume relationship of the soil. Almost every geotechnical textbook covers this and explains the various weight(mass)-volume relationships that are calculable for soil/water/air systems.

Using this basic relationship: V=Ms/(Gs x Unit weight of water), you can determine essentially all of the weight-volume relationships of soil, compacted or otherwise, with only the wet unit weight of the soil and the moisture content, determined through density testing of the soil.

Agree with BigH that the term "solid density" has no real meaning in geotechnical engineering/soil mechanics.