×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Calculating the Unit Weight of In-Situ Soils

Calculating the Unit Weight of In-Situ Soils

Calculating the Unit Weight of In-Situ Soils

(OP)
Can anyone out there give me insite on current testing methods for calculating the In-situ unit weight of soils?  We are constructing a gravity sewer and would like to calculate the specific gravity of the material we are excavating, so we can backfill with a similar weight material.  Any help would be greatly appreciated! :)  Thank you!

RE: Calculating the Unit Weight of In-Situ Soils

In-situ density tests are usually conducted using either a sand cone density apparatus (standard test ASTM D1556), or a rubber-balloon equipment (ASTM D 2167). Both are approved techniques by ASTM Standards. There is also a nuclear density test apparatus (standard test ASTM D2922), but equipment is more expensive and must be operated by specialist technicians.

the sand cone is basically a method to dig out the in-situ soil (and weight it), then fill the hole back with a known specific type of sand to get the volume of soil removed. So density = weight/volume.  In balloon method, you fill the void created by digging using a rubber ballon filled with water. Volume of water in the balloon can be easily calculated (specific gravity of water = 1)

I don't think you are going to check the specific gravity of the soil.... just the unit weight or in-situ density. Specific gravity test is a different test... it is in a way similar to a measure of weight/volume of the actual mineral aggregates/soil, excluding the voids, etc.

Soil labs usually do the in-situ density tests for you. To check whether the backfill material has good density (good compaction)... or to compare it with the density of the original materials.  

Regards

RE: Calculating the Unit Weight of In-Situ Soils

(OP)
Yes, Sorry!  I meant to type density instead of specific gravity in the 2nd sentance.  :)

RE: Calculating the Unit Weight of In-Situ Soils

If the soil is saturated,and you have measured the water content (a $10.00 test)  you can assume a specific gravity for the soil (2.65 for sand and 2.7 for clays are typical values) and then use the following equation to estimate the total unit weight:

((1+w)(gamaw))/(w + 1/G)     where G= specific gravity
                             gamaw =unit weight of water
                             w= water content of soil
If the soils to be excavated are cohesive, you can push Shelby tubes into the soil and determine the unit weight of the soil in the laboratory.  There are correlations between the standard penetration resistance and soil unit weight in the literature--you may want to look in any basic soil mechanics textbook for these correlations.

RE: Calculating the Unit Weight of In-Situ Soils

What about insitu nuclear density measurement?

RE: Calculating the Unit Weight of In-Situ Soils

Hello, can anyone tell me the difference between unit weight and density?

RE: Calculating the Unit Weight of In-Situ Soils

In practical terms, at least on planet Earth, they are the same.  
The difference is actually that density is mass over volume, and unit weight is weight over volume.  Since we are always going to be considering gravity, density will have to take it into account, also.    
All ASTMs that deal with density are actually dealing in unit weight. Trust me!  This is true.  If you look at the proctor test, nuke test or the sand-cone test, all use WEIGHT over volume, and not mass over volume.  So if you are looking at it from the angle of an ASTM, they are going to be the same there, too.  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources