I have a newly installed 24" Ribbed PVC pipe that is not yet in service. It has about 15' of cover. In the pipe zone it has clean washed sand to 1 ft above the crown. The backfill above the pipe zone is a sandy clay compacted pretty tight, say 95% proctor, all the way up. The pipe was air tested but when a 5% mandrel was tried, it would not enter the pipe. Video inspection shows a consistent egging along the entire length of the pipeline. Short of digging it up and relaying it, are there other options to 'repair' the egging and get it back to near round?
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PVC Pipe Deflection - Egging 8
- Thread starter sewerratt
- Start date
ACtrafficengr
Civil/Environmental
It's easier to prevent than correct.
What's below the pipe? It probably wasn't bedded well when it was installed.
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"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."
Wm. Phelps Eno, ca. 1928
What's below the pipe? It probably wasn't bedded well when it was installed.
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"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."
Wm. Phelps Eno, ca. 1928
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- Thread starter
- #4
It has at least 5% vertical deflection. Our spec requires a 5% mandrel to pass and it won't even go in. ASTM says 7.5% is limit. Manufacturer says 30% is where the 'flip' is for structural failure. The bedding is clean washed sand from 6" below the pipe to 1' above. Compaction of that pipe zone is likely the culprit. This line reroutes an adjacent line that is running very well and in good shape. Don't want to trade down, if you know what I mean. Contractor is looking at an expensive fix and I am just looking for some information from the forum to help evaluate any options he suggests. As for the a-r issue, the egging is now, two weeks after installation. Long term consolidation will likely add more. Round pipe is round. Structurally, tires will still function if egg shaped, but it makes for a hell of a ride and you won't find them on the brand new Chevys.
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Interesting. One particular respondent is certainly not giving the experts who write standards and specifications that limit installed deflection, perhaps including many in the plastic pipe industry, much credit!!! I happened to see that problems with some sort of ribbed plastic pipes were also discussed not long ago on the thread at I’m not going to speculate on the cause nor responsibility for specific problems mentioned there nor here; however, just a couple sort of philosophical design questions -- it would appear that manufacturers furnish "ribbed" or "profile-walled" pipes to minimize material cost, while at the same time in various proprietary means maximizing at least the short-term ring stiffness of the pipe as measured by ASTM standard plastic pipe ring tests (at least of course compared to say a solid-walled pipe with the same kind/amount of material). In the case of plastic pipes, I believe these ring tests are usually accomplished in a laboratory ring-crushing machine at a quite rapid (I think at about a ½” diameter-inch/minute) loading rate. However, is it possible that in practical field circumstances, with all else being equal in “design” (e.g. a given amount of maximum design ring deflection allowed in the field?), this could near inevitably result in some high, and perhaps even significantly higher localized stress/strain in the wall of the profiled pipes than is envisioned in normal plastic pipe design? In other words, though with perhaps comparable at least short term stiffness the wall/arch of a ribbed pipe is in essence a generally “thicker” or deeper curved beam (from the extreme outside of the profile to the inside of the profile wall), and it will inevitably exhibit greater stress/strain in the extreme fibers etc. (in the Mc/I, and maybe even shear sense of the wall cross-section etc.) if it is allowed to be ring deflected in the field the same amount as a less deep, more flexible curved beam (e.g.. a. solid wall pipe of the same diameter)/ pipe manufactured e.g. with the same weight amount/ unit length of material? Is it possible also that this greater amount of stress/strain could even be some additive in some locations to some residual stresses in the material as a result of perhaps more stressful formation of the profile/corrugations, dependent on method of manufacture? In addition, it would also appear profile-walled pipes also might not have the longitudinal (or length-wise) bending strength of solid-walled pipes, depending on corrugation design.
Would all this increase the likelihood of eventual (stress, strain, creep or small wall defect-related?) problems, that may not generally have been observed (or observed yet/much?) in solid wall pipes of the same materials, even in the absence of obvious UV or fire-related problems? In the case of pipes buried very shallow, deep or at the toe of embankments, etc. is it even possible that what goes on in the axial direction could also be a complicating factor in eventual problems with this kind of piping?
There are some interesting durability references describing research on/aspects of deflected profile-walled plastic pipes (in that case I think hdpe) that indicate there apparently has to be some significant control over depth of cover, backfill materials, compaction, construction, and then also subsequent measurement of deflection to assure a long life of these pipes (it may be less clear how all this is practically accomplished in the field). See , with the interesting quote on page 20, “To ensure long-term performance, the individual pipe wall profile must be evaluated in regard to its specific geometry, and the stresses and strains quantified to properly determine the long-term capacity of the specific materials allowed.” (it may not be exactly clear who is going to do, and or be “responsible for doing, this??) See also the detailed report at , also with many of the aforementioned caveats in an attempt to assure long life… It is interesting also to see in apparent KY DOT document at concerning field deflection testing of plastic pipes (see pgs 701-5 thru 701-8, and particularly see scheduled reduced payment terms advocated vs. level of measured pipe deflection on pg 701-8!)
Would all this increase the likelihood of eventual (stress, strain, creep or small wall defect-related?) problems, that may not generally have been observed (or observed yet/much?) in solid wall pipes of the same materials, even in the absence of obvious UV or fire-related problems? In the case of pipes buried very shallow, deep or at the toe of embankments, etc. is it even possible that what goes on in the axial direction could also be a complicating factor in eventual problems with this kind of piping?
There are some interesting durability references describing research on/aspects of deflected profile-walled plastic pipes (in that case I think hdpe) that indicate there apparently has to be some significant control over depth of cover, backfill materials, compaction, construction, and then also subsequent measurement of deflection to assure a long life of these pipes (it may be less clear how all this is practically accomplished in the field). See , with the interesting quote on page 20, “To ensure long-term performance, the individual pipe wall profile must be evaluated in regard to its specific geometry, and the stresses and strains quantified to properly determine the long-term capacity of the specific materials allowed.” (it may not be exactly clear who is going to do, and or be “responsible for doing, this??) See also the detailed report at , also with many of the aforementioned caveats in an attempt to assure long life… It is interesting also to see in apparent KY DOT document at concerning field deflection testing of plastic pipes (see pgs 701-5 thru 701-8, and particularly see scheduled reduced payment terms advocated vs. level of measured pipe deflection on pg 701-8!)
Well, I'm a little skeptical of 30%. However, I wouldn't hesitate at 10 to 15%. I wouldn't worry about it. Check NRCS procedures on flexible pipe - as it eggs it consolidates the resistance (not to be confused with consolidating clay) increasing the structural competency of the surrounding backfill - and the NRCS is typically *very* conservative, yet thorough in design analyses. The problem would be if it's under a roadway and you might expect additional consolidation adjacent to the backfill. The biggest problem with HDPE is compaction under the shoulders. As you compact under there it floats - every movement means the pipe is rising. I always recomment flowable fill to about the 1/4 point to prevent piping - drop it directly on the pipe to aid in floatation resistance.
- Thread starter
- #7
thanks rconner, for the links, they were real useful. Two were for HDPE Storm pipe. My application is PVC sanitary pipe. I noted most folks were commenting on HDPE. Is there any significant difference in their long-term stress and deflection performance, given the same bedding? I know bedding IS critical for either material and I believe in ACtrafficengr's note that 'It's easier to prevent than correct.' I chalk this situation up to the contractor's inexperience with this product. 57 angular stone was required in the pipe zone and it was not installed. fortunately, he has made the time to fix it (but not the time to do it right the first time! Isn't this always the case) The solution currently being implemented is removing the backfill and the pipe zone material to 1/4 pipe height and going back up with vibrated 57 angular stone to the crown and then rebackfilling with the original material. When a short section was checked, the pipe had sprung back to within acceptable deflection. An expensive solution, but this contractor is an outstanding company with a great reputation for doing good work.
semo
Civil/Environmental
- Oct 16, 2003
- 303
I had a project once where the pipe was installed with native material as bedding. Assuming that the bedding wasn't compacted and spaces were left under the haunches of the pipe, the pipe deflected as in your case.
It did not pass the 5% deflection rule either. We allowed the contractor 10% deflection; but, there were still areas where a 90% mandrel did not pass. These areas were dug up and recompacted.
Once uncovered the pipe sprung back into shape and after reinstalling the fill properly, these areas of the pipe passed the 5% deflection test.
I had no real support documentation for allowing 10%; however, the pipe has performed fine for approximately 8 years now. It does not have heavy traffic over it however.
It did not pass the 5% deflection rule either. We allowed the contractor 10% deflection; but, there were still areas where a 90% mandrel did not pass. These areas were dug up and recompacted.
Once uncovered the pipe sprung back into shape and after reinstalling the fill properly, these areas of the pipe passed the 5% deflection test.
I had no real support documentation for allowing 10%; however, the pipe has performed fine for approximately 8 years now. It does not have heavy traffic over it however.
- Thread starter
- #10
All other installations of the same pipe material and diameter, at greater depths, that have been installed in our system met the deflection requirement. Perhaps future installations will be DI pipe, but with the corrosion issues of sewage when you get to pipes this size, a noncorrosive material is required.
I really don't see 5% as tight. Pretty much an industry standard. As the owner, we have to maintain this pipe for its life and pay to replace it when it's over. So we have standards. Developers, contractors and consultants are gone after the last lot is sold, the retainage is released, or final payment is made.
Missing in all the discussion is my original question: Any way to fix it without digging it up? Moot now, since that's what we're doing. But, it sounds like there are no other options.
I really don't see 5% as tight. Pretty much an industry standard. As the owner, we have to maintain this pipe for its life and pay to replace it when it's over. So we have standards. Developers, contractors and consultants are gone after the last lot is sold, the retainage is released, or final payment is made.
Missing in all the discussion is my original question: Any way to fix it without digging it up? Moot now, since that's what we're doing. But, it sounds like there are no other options.
PVC sewer lines typically mandrel’s outside dimension sized to permit 7.5 percent deflection.
For non-pressure PVC pipes, installation requirements can be found in the ASTM D2321, “Standard Practice for Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity-Flow Applications, ASCE Manual No. 60 / WPCF Manual FD-5, “Gravity Sanitary Sewer Pipe Design and Construction.”, and Canadian Standards Association’s (CSA’s), “Recommended Practice for the Installation of Thermoplastic Drain, Storm and Sewer Pipe and Fittings” .
For non-pressure PVC pipes, installation requirements can be found in the ASTM D2321, “Standard Practice for Underground Installation of Thermoplastic Pipe for Sewers and Other Gravity-Flow Applications, ASCE Manual No. 60 / WPCF Manual FD-5, “Gravity Sanitary Sewer Pipe Design and Construction.”, and Canadian Standards Association’s (CSA’s), “Recommended Practice for the Installation of Thermoplastic Drain, Storm and Sewer Pipe and Fittings” .
sewerrat,
With regard to your questions, pvc and hdpe are both plastic pipes, and (unlike steel and ductile iron) both have much lower initial as well as vastly different "initial" and "long term" (e.g. "50-Year") tensile strengths and moduli, respectively. These different values are e.g. illustrated on pg 31 in a table from a very large city's bureau of engineering document, "Figure H211.41A - Long Term (50 year) Tensile Strength & Modulus of Elasticity of Structural Plastics for Piping" at As can be seen though in this table, pvc does have a slightly higher long-term modulus and strength than does hdpe. I suspect for this reason, it appears hdpe has in some cases (to minimize material cost?) perhaps tried a little harder to market some pipes with even less long-term stiffness than pvc?
When it comes to design, some folks in the past for both types of pipes have advocated use of the higher initial, very short-term modulus (e.g. stiffness determined in a laboratory compression testing machine ring test at a very rapid loading rate of ~ 1/2 inch diameter/min.) in design for long-term service. As earthloading etc. over many years is arguably much more inexorable (and can get pretty "heavy", with rainfall etc., over time!), others (like it appears the authority referred to) want instead consideration of long-term properties for long-term service.
In any case, it is good this problem was detected and is reportedly being corrected by an outstanding contractor while he is still in the area/willing to do this -- it appears some others have perhaps not been as fortunate.
With regard to your questions, pvc and hdpe are both plastic pipes, and (unlike steel and ductile iron) both have much lower initial as well as vastly different "initial" and "long term" (e.g. "50-Year") tensile strengths and moduli, respectively. These different values are e.g. illustrated on pg 31 in a table from a very large city's bureau of engineering document, "Figure H211.41A - Long Term (50 year) Tensile Strength & Modulus of Elasticity of Structural Plastics for Piping" at As can be seen though in this table, pvc does have a slightly higher long-term modulus and strength than does hdpe. I suspect for this reason, it appears hdpe has in some cases (to minimize material cost?) perhaps tried a little harder to market some pipes with even less long-term stiffness than pvc?
When it comes to design, some folks in the past for both types of pipes have advocated use of the higher initial, very short-term modulus (e.g. stiffness determined in a laboratory compression testing machine ring test at a very rapid loading rate of ~ 1/2 inch diameter/min.) in design for long-term service. As earthloading etc. over many years is arguably much more inexorable (and can get pretty "heavy", with rainfall etc., over time!), others (like it appears the authority referred to) want instead consideration of long-term properties for long-term service.
In any case, it is good this problem was detected and is reportedly being corrected by an outstanding contractor while he is still in the area/willing to do this -- it appears some others have perhaps not been as fortunate.
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I believe that the contractor should excavate the material and relay it at his cost. What is the point of having standards and specification if they are going to be relaxed as soon as the contractor stuffs up? By letting the contractor get away with it you lose all crdibility. WHats he going to do next time ? Ignore the specification because he knows you dont mean it? That not only makes it tough for you but for the whole engineering fraternity.
Thats like letting your kids run riot in the house. If parents dont discipline the kids when they misbehave you create the monsters we have in society today. Havent you watched Super Nanny on TV?
I serve on three plastic and buried pipeline standards committees. The plastic industry uses standards as a marketing tool. They try to gewt the requirements as low as they possibly can as they compete with vitrified clay, ductile iron, steel, GRP etc.
Its amazing the plastic industry develops a product, demand there be a national standard and when it fails claim it meets the same national standard that they demanded!
The pipe may not be uniformly deflected into an egg shape. There may be local deflection that exceeds the strainlimit of the material. The pipe may buckle due to long term loads.
Suggested reading:
AS 2556 Buried Flexible Pipelines
Buried Pipe Design Moser
Structural Mechanics of Buried Pipelines Watkins & Anderson
Deformation and Fracture Mechanics of Engineering Materials Hertzog
Plastic Pipes for Water and Waste Water Lars Eric Janson
Thats like letting your kids run riot in the house. If parents dont discipline the kids when they misbehave you create the monsters we have in society today. Havent you watched Super Nanny on TV?
I serve on three plastic and buried pipeline standards committees. The plastic industry uses standards as a marketing tool. They try to gewt the requirements as low as they possibly can as they compete with vitrified clay, ductile iron, steel, GRP etc.
Its amazing the plastic industry develops a product, demand there be a national standard and when it fails claim it meets the same national standard that they demanded!
The pipe may not be uniformly deflected into an egg shape. There may be local deflection that exceeds the strainlimit of the material. The pipe may buckle due to long term loads.
Suggested reading:
AS 2556 Buried Flexible Pipelines
Buried Pipe Design Moser
Structural Mechanics of Buried Pipelines Watkins & Anderson
Deformation and Fracture Mechanics of Engineering Materials Hertzog
Plastic Pipes for Water and Waste Water Lars Eric Janson
dicksewerrat
Civil/Environmental
When you install flexible pipe, you MUST compact all the fill, not just the stuff above the pipe. The only reason this pipe 'egged' is because the soil around the pipe does not give any support. Unfortunately ,clean sand doesn't compact worth a DA... the virgin soils, clay silt gravel compacts better. Have your contractor start digging it up. while this is happening have him read the ASTM standard for installing plastic pipes. then have the pipe supplier come out and watch the re-installation.
Richard A. Cornelius, P.E.
Richard A. Cornelius, P.E.
Dickseweratt nailed it...its the lateral pressure resistance that is failing, not the vertical, so compaction above and below might be just fine. It is difficult to compact the lower quadrants of pipe backfill.
You might consider doing a chemical stabilization (expansive foam type) to put lateral pressure on the pipe. Since you have clean sands around the pipe, this should work well. Use something like PrimeFlex 910 with a higher than typical catalyst percentage to increase the pressure during expansion. Once it has set, it will stay. At the least it will likely prevent the pipe from flattening any more. Pressurize the pipe with air to help equalize while you do the chemical grouting.
Clean sand is easy to compact...it's just not very stable, even when compacted.
Cheaper and easier than uncovering and re-setting.
You might consider doing a chemical stabilization (expansive foam type) to put lateral pressure on the pipe. Since you have clean sands around the pipe, this should work well. Use something like PrimeFlex 910 with a higher than typical catalyst percentage to increase the pressure during expansion. Once it has set, it will stay. At the least it will likely prevent the pipe from flattening any more. Pressurize the pipe with air to help equalize while you do the chemical grouting.
Clean sand is easy to compact...it's just not very stable, even when compacted.
Cheaper and easier than uncovering and re-setting.
- Thread starter
- #16
Like I said, he IS digging out the backfill and the pipe zone material to below the springline and backfilling with compacted crushed stone to above the pipe, then backfilling with his original material.
To address some of the comments, the intention was never to relax our standards, only to have information on possible options before the contractor proposed them. That was not necessary, as he proposed the option of digging it up and replacing the pipe zone material with better stuff. We are strong proponents of 'dig it up and replace it'. In our jurisdiction, we require the contractor and the developer to sign an agreement and post a bond before project approval that guarantees the work will meet our specifications. We will not release the bond or the agreement until it does. If they resist, we cash out the bond and pay someone else to do right. Its a takeoff on the golden rule of business. He who has the gold makes the rules.
I'm real appreciative of the comments and information posted here. There has been some excellent help given, especially with reference materials and longterm performance issues. Thanks
To address some of the comments, the intention was never to relax our standards, only to have information on possible options before the contractor proposed them. That was not necessary, as he proposed the option of digging it up and replacing the pipe zone material with better stuff. We are strong proponents of 'dig it up and replace it'. In our jurisdiction, we require the contractor and the developer to sign an agreement and post a bond before project approval that guarantees the work will meet our specifications. We will not release the bond or the agreement until it does. If they resist, we cash out the bond and pay someone else to do right. Its a takeoff on the golden rule of business. He who has the gold makes the rules.
I'm real appreciative of the comments and information posted here. There has been some excellent help given, especially with reference materials and longterm performance issues. Thanks
If you take it out and replace it "with better material" the contractor can argue that the reason there was a problem was because the backfill material that was spec'ed was not good enough, and someone else will have to pay him to do the work. It's called Errors and Omissions insurance...
- Thread starter
- #18
The developer's engineer designed the job to meet our minimum standards and specifications, which allow 57 stone, pea gravel or washed sand as acceptable materials for the deisgner to consider, but those same specs are performance specs that require it to pass the 5% deflection criteria, among other things, before we accept it for maintenance. The contractor may have a beef, but it will be with the design engineer.
Sewerratt,
Have you considered that the native soil at that depth was unable to resist the loading from the soil above the pipe. At such depths MArston's theory could be used that includes for soil friction (refer AS 2566 Commentary). This may reduce the vertical loading but doesnt eliminate it.
If the native soil is not sufficntly strong then the blame may lie with others than the contractor. Did the Principal commission the soils analysis? Was the Principal or contractor responsible for on site soils testing during the excavation? Was the site superintendent responsible for approving the results of the on site soils testing?
I have a problem with not allowing the contractor to rectify the problem if he is to blame. Case law in Australia would rule that you have denied natural justice. On the other hand if the contractor has signed up to a contract with these provisions it would be a murky court case.
Have you considered that the native soil at that depth was unable to resist the loading from the soil above the pipe. At such depths MArston's theory could be used that includes for soil friction (refer AS 2566 Commentary). This may reduce the vertical loading but doesnt eliminate it.
If the native soil is not sufficntly strong then the blame may lie with others than the contractor. Did the Principal commission the soils analysis? Was the Principal or contractor responsible for on site soils testing during the excavation? Was the site superintendent responsible for approving the results of the on site soils testing?
I have a problem with not allowing the contractor to rectify the problem if he is to blame. Case law in Australia would rule that you have denied natural justice. On the other hand if the contractor has signed up to a contract with these provisions it would be a murky court case.
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