×
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

Compaction of fills on a slope

Compaction of fills on a slope

Compaction of fills on a slope

(OP)
I've run into a few sites where my fellow geotechnical engineers have written specifications requiring uniform horizontal lifts. I've had some back and forth with different senior engineers but I'm still searching for a good reason for this specification and why they are so stringent on enforcing it.

Suppose you have a 6:1 slope, and you place and compact a uniform lift on the slope, with the same 6:1 slope. Why is that different than placing a uniform lift of the same thickness on horizontal ground? Usually these particular geotechs insist on placing overbuilt horizontal lifts on the 6:1 slope and then trimming them to grade at the end (imagine an overbuilt staircase of lifts if you would).

So, here's the million dollar question: Do the soil particles on the 6:1 slope know that they have been placed on a slope, and that they therefore are required to perform worse? Or do they only know that they've been compacted to whatever arbitrary percentage of SPMDD or MPMDD that particular consultancy has pulled out of their collective behinds?

As an aside, I always like asking them how they know compacting it to that percentage of SPMDD will achieve the shear strength and compressibility parameters they are looking for. No one has ever answered. I had one company that had assumed 1900 kg/m&^3 in a slope/w model, but all the fill was placed and compacted to 98% SPMDD, with a resultant of around ~1750 kg/m^3. Upon questioning the response was 'we know better than you'. Anyway, now I've gone off on a tangent.

RE: Compaction of fills on a slope

Quote:

Suppose you have a 6:1 slope, and you place and compact a uniform lift on the slope, with the same 6:1 slope. Why is that different than placing a uniform lift of the same thickness on horizontal ground?

IMHO, a one word cause... Gravity.

Any real-world compactive equipment either uses or is affected by gravity.

On a horizontal surface all compactive energy is used for it's intended purpose - soil compaction.

On a sloped surface some of the compactive energy is directed parallel to the sloped surface. Remaining energy that is perpendicular to sloped surface is reduced a little, but that is usually minor compared to the disruptive "sideways" component.



www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Compaction of fills on a slope

(OP)
So the issue is that it's harder to achieve the targetted compaction?

Supposing that you actually achieve the SPMDD target, there should be no issue then?

I've also heard the argument that the requirement is based on nuclear densometers not working on a slope, based on an older version of the ASTM standard which implies this is the case.

RE: Compaction of fills on a slope

Agree with SRE; however, when you achieve compaction, you're done. It's less efficient for compaction purposes, but if you achieve the result, no issue other than extra time.

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


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close