Percent Voids for Gravel 3

[HoustonStructural]

I am using gravel as a bedding underneath an open bottom valve/drain box and im not sure what percentage of voids we should assume for gravel? Any help on this issue, I would appreciate it.

 

[DMcGrath]

I have that question come up now and then too, but for different reasons. I found this a while ago:

http://www.stormtech.com/pdf/StormTech - Tech Sheet 1 - Porosity of Structural Backfill.pdf

 

[civilperson]

30-40% void is normal for gap graded gravel.

 

[fattdad]

I'd use 1/3rd. Bear in mind that you can also measure it yourself. Take the specific gravity of the aggregate, multiply it by the unit weight of water and that would be the density if there were no voids. Then take the bulk density of the aggregate and figure out how much is lost to air voids.

Example:
Specific gravity of the aggregate is 2.7
void-free density would then be 168.5 pcf
bulk density (dry) of the aggregate is 112 pcf.
void ratio is 1-(112/168.5)=0.34

Hope this helps.

f-d

¡papá gordo ain’t no madre flaca!

 

[DMcGrath]

On a somewhat related note...

http://blog.thylmann.net/2003/10/23/there-is-always-room-for-beer/

 

[msquared48]

I use 30% for infiltration trench storage.

Mike McCann
MMC Engineering

 

[psmart]

If you have a sample of the material, it's easy to measure. Fill a gallon container with the gravel and see how much water you can add.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Ron]

psmart...only valid if the aggregate is saturated, surface dry. If the aggregate is completely dry, then can be off by as much as 5 or 6 percent, depending on absorption.

Use weight-volume relationship as suggested by fattdad.