Meaning of Passes

[BigH]

Problem:

Specification says that the contractor shall carry out 6 passes of a 15 ton vibrating smooth drum compactor.

What is a pass?
Is it a round trip?
Is it a single pass-over?

Most specs are "mute" on this. Wanting to see what kind of variation in responses - and by country.

 

[CarlB]

BigH, you asked this question 2 years ago, I knew it sounded familiar.
My vote- a single pass-over.
Do compactors always retrace their paths?
Alaska, USA.

 

[jgailla]

From north Florida and south Georgia, a single pass-over, not round trip.
I don't think I've ever had this issue come up before.
If I was a contractor who read that statement, I would do 3 trips out and back. I don't think I'd take it kindly if an engineer told me I had to do more.

 

[BigH]

Sorry CarlB - Senior Moment - but hoping to get more responses - especially in Asian and African countries . . .

 

[hokie66]

Australia...six passes means the roller touches the surface six times, not necessarily three round trips.

 

[MiketheEngineer]

Square trips??

 

[fattdad]

I'm going with "B."

f-d

¡papá gordo ain’t no madre flaca!

 

[motorbiketocrank]

Single pass. US - mid atlantic.

 

[Hoaokapohaku]

A round trip is always two passes ... and that's an awful spec regardless of how one interprets the passes.

 

[Ron]

Each time rolling over same area is a pass.....from jgailla's land

 

[Drumchaser]

If, after you make a pass, she engauges...then you could be in for a round trip.

 

[BigH]

As many know, I am now in a SE Asian country. In the performance of a trial fill to which the contractor must carry out up to 12 passes, the contractor was ready to do it as 12 round trips ( which would be, for the record, 24 passes in my book) . . . and this isn't the first Asian country I've seen this "idea" in . . . Suggestion if one is involved in writing specs or soils reports for overseas projects (perhaps Asian countries) it might be a good idea to clearly define the meaning . . . I convinced the contractor that he only need to do 12 "single" passes . . .

I'm still interesting in those practicing in SE Asia or in the sub-continent to please give their understanding . . .

 

[Hoaokapohaku]

It's a good question to resolve, because with a vibratory roller, one pass too many most likely will REDUCE the density of the material being compacted. If any material takes 12 passes with a vibratory roller, no matter how you define a "pass", either it is the wrong roller for the job, the moisture content of the material is not optimal (far from it), or the lift is too thick. Any spec that requires either an odd or even number of passes with a vibratory roller has at least a 50% chance of being more or less than optimal by one, one-way pass.

 

[dgillette]

Six passes of a pretty large vib roller? Wow, that's a lot of good, good, good vibrations. What RD are you trying for and what lift thickness? That's not your filter, right? (Peck told us that for filters, 70% RD should be the max. He was concerned about particle breakdown -> loss of vertical permeability, and potential for brittle behavior and cracks.)

 

[BigH]

No, @Dave, it is not the filter . . . it is a clayey zone outside the core.

 

[dgillette]

Oh. I had assumed it was filter, drain, or granular shell. I don't often see smooth vib rollers on clay in the US, mostly padfoot rollers on smaller projects, and lots of 825s on bigger ones (stock, or with aftermarket drums having small circular classic sheepsfoot feet).

Have you ever done an experiment to see how much the vibration helps the density of clay? For a fairly small fill, the contractor brought a small radio-control vib padfoot. The vibration made a very small difference in the density, but that was the difference between barely making the density spec and just missing it.

DRG

 

[BigH]

Doing both smooth drum and padfoot on the trial embankment of the material - there is a difference between USA and SE Asia . . . . and what the contractor can or is willing to put on the job . . .

 

[dik]

BigH... using a smooth vibratory roller for clay? or did I misunderstand you? We typically use a sheepsfoot...

Dik

 

[BigH]

@dik - we are doing both . . . the equipment choice for the trial embankment is left to the contractor and then it is judged . . . I've seen a lot of smooth drum rollers used on clayey material (CI/MI) here in Asia.

 

[dik]

OK... I assume you can get the compaction... not been my experience with drum rollers... we have a very high plastic clay in these environs... compaction not spec'd by Proctor?

Dik