Side Compaction Of Stormwater Pipe - Excavation & Site Work - Contractor Talk

Side Compaction Of Stormwater Pipe

 
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Old 07-26-2008, 04:11 PM   #1
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Side Compaction Of Stormwater Pipe


A contractor is bidding a print of yours (okay, mine) that calls for 600 feet of 120" corrugated steel round pipe to have certain side compaction specs met, and installed in 8" lifts. When you inquire how that compaction will be measured, the contractor says, "Well, you just have to trust the contractor you hired. We do this all the time. We know how to do it". Would you buy that? I'm worried that if the compaction isn't measured, and it isn't well done up to the spring line of the pipe, the thing's gonna squish like a pop can. Is it ever accetpable to install pipe this large and not actually measure compaction? Additionally, there is a compaction spec on the print for the bedding of the pipe, and the contractor claims that the material he will use in the bed "falls to compaction". I've never heard of such a thing. Help me out with your opinions so a couple hundred K isn't wasted...

Last edited by mdshunk; 07-26-2008 at 04:14 PM.
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Old 07-26-2008, 04:54 PM   #2
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Re: Side Compaction Of Stormwater Pipe


If he is using stone for bedding he is fine we use alot of stone instead of compacting the bottom of trenches it saves alot of time. Stone does fall to compaction. as far as compacting during backfill 8" lifts is over doing it. 12" is more like the standard. if they use a sheeps foot trench roller and good gravel there will be no problem. where is this pipe located and what is the purpose of it. the only other thing you can do is hire a Geo tech company to do compaction testing.

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Old 07-26-2008, 05:04 PM   #3
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Re: Side Compaction Of Stormwater Pipe


I think stone of some kind would be the only fill i would use with out com paction and i would still run a plate over it every 8 " or so. Ive placed some large pipes under drive ways and roads with out anty problem I see guys backfilling all the time with out compaction . Whats up with that?
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Old 07-26-2008, 08:55 PM   #4
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Re: Side Compaction Of Stormwater Pipe


Not sure where this is, but a lot of towns and state roads are requiring K-Crete in its in the street. Yes, the entire trench can only be backfilled with k-Crete. They are requiring this when private contractors dig up the roads and have to patch it up. For new or municipality projects, they do not use it.
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Old 07-29-2008, 08:30 PM   #5
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Re: Side Compaction Of Stormwater Pipe


He is right, just trust him.
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Old 07-30-2008, 11:11 AM   #6
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Re: Side Compaction Of Stormwater Pipe


"falls to compaction" depends on what kind of stone he's using, there are graded stone mixes (high performance bedding stone it's called here) that don't require compacting. Clear stone (usually 5/8" or 3/4") can be used without compaction but can cause voids to form later depending on ground conditions.
3/4" crushed stone can be compacted in small lifts with a plate tamper, but compaction should be tested by a geotechnical firm.
I'd go with testing, you can end up with lots of problems later on with large corrugated steel pipe, the bedding is an important factor in the strength of the pipe.
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Old 07-30-2008, 10:10 PM   #7
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Re: Side Compaction Of Stormwater Pipe


"In Theory", if the backfill material is at its optimum moiture content, and is droped from a certain height, it will land at something like 80% maximum density. Nothing will beat proper compaction methods though. Our spec here would be 95% max density for the pipe cousion on the bottom, 95 through the haunches, and 75% for the first 12" lift on top of the pipe, and 95% for the remaining lifts to the top of the trench. I would get the compaction "nuked" by the local soils engineer, if liability is an issue. We also use C.L.S.M here for trench backfill. (similar to k-crete?) C.L.S.M. is a lean concrete mix, about 500 psi, with a high water content, also call "flowable fill". it works well with D.I.P., but corrugated pipe might float in it, ive never tried!
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Old 07-31-2008, 06:28 PM   #8
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Re: Side Compaction Of Stormwater Pipe


Mdshunk,

I'm pretty sure words like "fall to compaction" and "trust" never appear in any spec.

To answer your question from an engineer's perspective. We usually ask for 8" lifts on more sensitive jobs, but 12" is more common. The line of thinking is "require 8 get 12, require 12 get 18". Nuke testing is the way to go with soils. If crushed stone is used we usually still require 12" lifts a few passes and just do a visual inspection. Flow-fill is also a good option. Another thing, we require a "proof roll in the presence of the engineer" before any fill or pipe or what ever is placed, just to ensure the natural subgrade is good. If soft areas are found they must be over excavated and backfilled.
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Old 08-02-2008, 02:14 PM   #9
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Re: Side Compaction Of Stormwater Pipe


I imagine he is going to use a clear buck shot material or rounded aggregate. No compaction is required with this material. If it is anything but clear rock (uniformly graded) then you have problems. I would ask for a sample of his back fill material prior to project start and consult a soil engineering firm prior to project start date. If he is using a sand back fill material very very clean, he may be able to hydro compact. I have done large storage tanks in this manner but it must be supervised by a competent person i.e engineering firm, with density tests. This is the only way to get compaction under the pipe but requires a place for the water exit through drain tile etc. It also requires a large source of water. Maybe you want to check his project references and see that he has done work in this order before you commit. He may be a very reputable contractor who installs this pipe all the time. Good Luck.

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