Pipe Zone Compaction
Pipe Zone Compaction
(OP)
We designed an underground detention system using 30" HDPE pipe. According to our details and ASTM 2321 the trench is supposed to have a minimum clearance between the pipe and the trench wall of 10", backfilled with compacted Class I or II material. The contractor instead set the pipe in a trench almost exactly the width of the pipe OD. In-situ soil in this area is generally fat clay.
When we told him he had to take the pipe out of the ground, widen the trench, and provide the required backfill he asked if he could leave the pipe in place, widen the trench as required, and backfill and compact the Class I or II material. My question is can this work? Can they widen the trench 10" on either side of the HDPE pipe without damaging it, and achieve the required compaction such that the pipe is adequately supported laterally?
When we told him he had to take the pipe out of the ground, widen the trench, and provide the required backfill he asked if he could leave the pipe in place, widen the trench as required, and backfill and compact the Class I or II material. My question is can this work? Can they widen the trench 10" on either side of the HDPE pipe without damaging it, and achieve the required compaction such that the pipe is adequately supported laterally?





RE: Pipe Zone Compaction
Adequate bedding is important UNDER the pipe. The 10" (I'd say that's insufficient for a 30" diameter pipe BTW) clear to the trench wall was so that you'd have enough room to compact the bedding below the pipe centerline. Placed in clay, is even worse. It will tighten up on the pipe. It should be sand placed around the pipe. Anyway, now you've got nothing there. Vertical load from above on the HDPE pipe will eventualy deform it and try to fold it into the now empty corners below the pipe. There is nothing to support it.
It will be your fault, because you knew about it, but did not object and make the contractor follow the installation specifications you gave him.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Pipe Zone Compaction
RE: Pipe Zone Compaction
With hand excavation, maybe they can expose it without mucking it up even more.
Keep a constant eye on them.
If you find even a hint of any damage anywhere, ... anywhwere, they should pull it all up.
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Pipe Zone Compaction
However, if the contractor can widen the trench and the pipe can be properly supported with good quality, compacted backfill, I think that process meets the specs. You may which to tighten the backfill requirements to Class II SW so the contractor is able to easily meet any compaction requirements.
Also, you want to make sure the backfill is well drained. You don't want any standing water (ie, saturated soils) in your backfilled trench or it will cause the clay sidewalls to swell and put unwanted lateral pressure on both the backfill and the HDPE pipe when the pipe is empty.
RE: Pipe Zone Compaction
If you are not going to do this instruct the contractor to lift the pipe and do it properly.
“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/
RE: Pipe Zone Compaction
I usually use bedding stone up to the diametre and then good granular material for the backfill. I'm not sure what Class I and Class II material are.
Dik
RE: Pipe Zone Compaction
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Pipe Zone Compaction
RE: Pipe Zone Compaction
Dik: The pipe is solely for detention. The outfall pipe is 12" HDPE with a restrictor pipe at the downstream manhole. I prefer underground detention because I think those big holes in the ground are a waste of good real estate in most cases. Plus, that's the only option when there's no room for a pond.
Ben: I put an underground detention system using 60" HDPE beneath the driveway and parking lot of a fire station back in 2003. It was installed per the plans and specs, and has continued to perform with no problems through one hurricane and despite the heavy vehicle loads.
RE: Pipe Zone Compaction
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Pipe Zone Compaction
“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/
RE: Pipe Zone Compaction
CLSM could be used to backfill with only minor vibration required (if any). but this requires some experience by the contractor to not float the pipe, maintain alignment and roundness. doesn't sound like your's has that experience. I think it would be far easier for them to just pull the pipe, fill one trench and re-dig the single wide trench per plan.
RE: Pipe Zone Compaction
What are you going to do if in the future a truck goes over the pipe, it collapses and someone is killed? What will you say tot he coroner? What will you say to your wife when you tell her "we have to sell the house darling to pay the lawyers".
Stick to the script its far easier in the long run.
“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/
RE: Pipe Zone Compaction
Dik
RE: Pipe Zone Compaction
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Pipe Zone Compaction
RE: Pipe Zone Compaction
Dik
RE: Pipe Zone Compaction
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Pipe Zone Compaction
I'm not sure what is wanted for right at 24" size, but guess it may be in general about 10 in. minimum for that size! I think somewhere else it is also stated this rationale basically also applies for multiple pipes in the same trench.
Hope this information also helps - everyone have a good weekend!
RE: Pipe Zone Compaction
RE: Pipe Zone Compaction
Richard A. Cornelius, P.E.
WWW.amlinereast.com