×
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 requirements for subgrade or fill below a pile supported slab?

Compaction requirements for subgrade or fill below a pile supported slab?

Compaction requirements for subgrade or fill below a pile supported slab?

(OP)
Are there any compaction requirements for the subgrade or fill below a pile supported slab (i.e. no reliance on the soil)?

We usually still call for 95% percent compaction on the standard Proctor, but I often wonder if this requirement could be relaxed since we aren't relying on the soil to support any of the building weight. But maybe there are other reasons why such a high level of compaction would be desirable.

RE: Compaction requirements for subgrade or fill below a pile supported slab?

In my view, so long as the soil can support the concrete until the slab has cured, no special requirements are necessary

Kieran

RE: Compaction requirements for subgrade or fill below a pile supported slab?

Are you compacting it before or after the piles are driven? If you're doing it after the piles are driven, it will be hard to access with large equipment.
I'm no expert, but I would compact to 95% before the piles are driven. You might have to add a little bit of soil after they're driven as the soil will tend to self compact due to the pile driving vibration.

RE: Compaction requirements for subgrade or fill below a pile supported slab?

(OP)

Quote:

Are you compacting it before or after the piles are driven? If you're doing it after the piles are driven, it will be hard to access with large equipment.

Usually before the piles are driven.

Quote:

I'm no expert, but I would compact to 95% before the piles are driven.

Why is 95% compaction needed? Why not something less stringent like 90% or even less?

RE: Compaction requirements for subgrade or fill below a pile supported slab?

Depending on the soil... I've used non-compacted fill... on several projects. If the slab is structural, no need to pack it down... even the slight loading from the plastic concrete will not likely cause consolidation in a short time.

Dik

RE: Compaction requirements for subgrade or fill below a pile supported slab?

I would use 95% because if the soil settles below the slab, a family of critters is likely to set up housekeeping. With 90% it's pretty much just dumped out of the dump truck.

RE: Compaction requirements for subgrade or fill below a pile supported slab?

Have you considered the compaction requirements for the piling rig access/stability?

RE: Compaction requirements for subgrade or fill below a pile supported slab?

That was my thought surely the piling mat will give you all need anyhow

RE: Compaction requirements for subgrade or fill below a pile supported slab?

Just a thought in another direction: we know that very often in piles, in presence of horizontal stress components, soil-foundation interaction is very sensible to conditions in the uppermost soil layer, so a greater rigidity of the fill might improve significantly pile behaviour under lateral loads. This of course if the thickness is not negligible at the scale of interest and if such horizontal components are not negligible themselves.

RE: Compaction requirements for subgrade or fill below a pile supported slab?

(OP)

Quote:

I would use 95% because if the soil settles below the slab, a family of critters is likely to set up housekeeping.

What kind of critters are we talking about here?

Quote:

With 90% it's pretty much just dumped out of the dump truck.

Oh, it's that easy to achieve 90%?

RE: Compaction requirements for subgrade or fill below a pile supported slab?

(OP)

Quote:

Just a thought in another direction: we know that very often in piles, in presence of horizontal stress components, soil-foundation interaction is very sensible to conditions in the uppermost soil layer, so a greater rigidity of the fill might improve significantly pile behaviour under lateral loads. This of course if the thickness is not negligible at the scale of interest and if such horizontal components are not negligible themselves.

Interesting point.

RE: Compaction requirements for subgrade or fill below a pile supported slab?

The surface needs to support construction loading, including the piling rig. However, compaction may be only part of the problem. Beware of conditions where the material under the slab is prone to volume change with moisture.

RE: Compaction requirements for subgrade or fill below a pile supported slab?

Quote (jedclampett)

With 90% it's pretty much just dumped out of the dump truck.

Really? Perhaps my location is different, but a typical load of granular material used for structural backfill weights approximately 100 lbs./c.f. in loose condition in a truck or stockpile and has a modified proctor of approximately 145 lbs/c.f., or 69% of modified proctor.

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