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pipeline clearance for vibratory compaction

pipeline clearance for vibratory compaction

pipeline clearance for vibratory compaction

Is there a standard recommended clearance for vibratory compaction of HMA mat overlying an existing pipepline? I have an existing waterline about 3.5 to 4 feet below the ashphalt layer being compacting. Is that enough clearance to use vibratory compaction method of the mat? I have been looking for a reference on this, but have yet to find anything substantial or conclusive. There is about 26-29 inches of clearance above the pipe. This material is predominantly SP or SM classification. The pavement section on top of the subgrade is 16 inches thick.

Thanks for your assistance.

- matt

RE: pipeline clearance for vibratory compaction

29 inches to finished grade or 29 inches to subgrade?

depends on what condition the pipe is in, bedding type and the type of pipe. If it is AC pipe, you may have a problem. If iron pipe probably ok.

RE: pipeline clearance for vibratory compaction

Thanks, cvg. It is 29 inches to subgrade. You did bring up a good point. I just checked and it appears the pipe is 12" diameter transite. So the scenario is roughtly 3.5 feet to the top of the transite pipe.

RE: pipeline clearance for vibratory compaction

Also, did you install that backfill? If it's forensic there's a good chance you would be compacting it for the first time, which would put pressure on the pipe. I would check your local ordinances to see what the minimum pipe depth for utilities is in the area, too. That might clue you into what they've experienced in the region as far as plastic? pipes go.

RE: pipeline clearance for vibratory compaction

PS. If you're talking about an overlay, I think that at the eleveation of your grinded layer, the 10+(or however many) lower layers would have bridged that utilities trench a long time ago.

RE: pipeline clearance for vibratory compaction

Providing the pipe backfill was properly placed and compacted, you have nothing to worry about whatsoever at that depth. Actually, even if the backfill is not compacted properly, you won't have any immediate damage to the waterline. Off the top of my head, I'm not sure what the minimum cover is, but I am sure that you have much more cover than the mimimum.

In addition, HMA compaction is high frequency, low amplitude. If any problem were to occur, it would happen during the compaction of the pipe, subbase, or base where higher amplitude vibration is used. But even at that, shouldn't be a problem.

RE: pipeline clearance for vibratory compaction

transite is very brittle and likely old, use care or you could damage it

RE: pipeline clearance for vibratory compaction

I don't think that 30 inches is OK especially for plastic pipes, clearance should be blarger

RE: pipeline clearance for vibratory compaction

"Transite" is a brand name of formerly produced asbestos cement pipe (or ACP, see e.g. http://en.wikipedia.org/wiki/Transite), a comparatively brittle piping material with I believe the likelihood of beam breaks in general going up as pipe size gets smaller and bedding gets less uniform/quality. It is my understanding ACP is longer manufactured in the USA.

RE: pipeline clearance for vibratory compaction

I'd look at upgrading that pipe before you put down the street. It will be much cheaper to rehab it now than in 2 years.

Richard A. Cornelius, P.E.

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