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.

 

[BigH]

Well, that's why we are doing the trials - the material at present is not overly plastic; compaction to be 95%. I'm more "worried" about ensuring no torturous water paths through the material. Thanks, dik and others, for your interest.

 

[Hoaokapohaku]

My experience is the same as Dik, no success with smooth drums on clay. If the smooth drum roller leaves traverse checking on the surface, that's typical of clay and a sure sign the roller isn't doing the job.

If your spec is by percent of proctor, why be concerned about the number of passes?

 

[BigH]

This is a big dam site, Hoaokapohaku. At present, we are looking at an embankment trial that will help us evaluate the most appropriate means and methods (remember, the contractor had a choice of equipment - so he has chosen to try a smooth drum roller in addition to a padfoot). As for the number of passes, it is important to the contractor (and us) to know how many passes he needs to make to reach the compaction needed. Considering perhaps more than 280 layers, the time element is very important - if it takes 8 passes to reach specification limit rather than 6, it may mean several weeks or longer of additional compaction over the course of the dam construction. On a highway project where the embankment is only a couple of metres high, it is not as critical.

 

[Hoaokapohaku]

Thanks BigH...that helps me understand. If the project were my responsibility, this would definitely be one of those "spare no reasonable expense to get the optimal compaction equipment" kind of projects, which is probably the 825's that dgillete mentioned earlier. But like you have said, you're in SE Asia and you must work with what you have.

 

[dgillette]

Big H - Suppose you could post some photos of test pits in the fill, for my enlightenment/entertainment? Would love to see how the lift contacts compare with the two different rollers. What would be really cool, though probably not possible, is to see how they compare after another 10-20 m of fill have been placed over them. Would they be consolidated to form one tight, coherent impervious mass, or would there still be discontinuities (potential locations for initiation of piping)?

 

[eea]

I assume you don't have handy access to testing equipment, but regardless of the specifications I'd do a quick nuclear density growth curve with the material at hand and see what the field conditions are during compaction. As many mentioned, too many passes could put you on the backside of the growth curve proctor test.

As much as the Contractor would like to just windup and go on a project, they need to adjust for actual conitions. Can I get density in 3 passes, maybe if the moisture % is just so. It is usually the Contractor's "means and methodology" to balance if they want to cover the cost of additional moisture (a water wagon) or drying (disking and waiting) versus adding additional passes with the roller to achieve target density.

All that being said, the 6 pass specification is more of a performance specification and opens the designer and owner to liability for field conditions they can;t really control, some of which are present by the Contractor's choosing (ie. moisture, equipment - too heavy or too light of a roller, ...)