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PVC Pipe Deflection - Egging
8

PVC Pipe Deflection - Egging

PVC Pipe Deflection - Egging

(OP)
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?

RE: PVC Pipe Deflection - Egging

It's easier to prevent than correct.

What's below the pipe? It probably wasn't bedded well when it was installed.

------------------------------------------
     "...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

RE: PVC Pipe Deflection - Egging

How badly is it egged?  With a flexible pipe egging problems are more of an anal-retentive problem than an actual hydraulic or structural problem.

RE: PVC Pipe Deflection - Egging

(OP)
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.

RE: PVC Pipe Deflection - Egging

3
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 http://www.eng-tips.com/viewthread.cfm?qid=128272&page=9.  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 http://www.dot.state.fl.us/research-center/Completed_Proj/Summary_SMO/FDOT_757_rpt.pdf , 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  http://www.dot.state.fl.us/rddesign/dr/PAG/PE%20Pipe%20S.L/Installation%20Final%20Report%208-3-03.pdf , 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 http://transportation.ky.gov/construction/spec/2k/division700.pdf 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!)


RE: PVC Pipe Deflection - Egging

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.  

RE: PVC Pipe Deflection - Egging

(OP)
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.

RE: PVC Pipe Deflection - Egging

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.

RE: PVC Pipe Deflection - Egging

With a tight dimensional requirement is Ribbed PVC pipe the right material?

RE: PVC Pipe Deflection - Egging

(OP)
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.

RE: PVC Pipe Deflection - Egging

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” .

RE: PVC Pipe Deflection - Egging

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 http://eng.lacity.org/techdocs/str-man/h-200.pdf.  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.        

RE: PVC Pipe Deflection - Egging

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

RE: PVC Pipe Deflection - Egging

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.
WWW.amlinereast.com

RE: PVC Pipe Deflection - Egging

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.

RE: PVC Pipe Deflection - Egging

(OP)
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

RE: PVC Pipe Deflection - Egging

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...

RE: PVC Pipe Deflection - Egging

(OP)
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.

RE: PVC Pipe Deflection - Egging

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.

RE: PVC Pipe Deflection - Egging

It sounds like someone mixed material specs with performance specs.  In those cases the advantage definitely does *not* go with the spec writer...

RE: PVC Pipe Deflection - Egging

3
This is a never ending debate.  

How much deflection can a thermoplastic pipe withstand without distress?  You say it is a profile wall pipe, which makes this a much tougher question to answer since the amount of bending induced strain in the pipe wall is dependent on the profile.  However, my general sense is that 5% is too restrictive, and the manufacturer claim of 30% is way too much.

From a theoretical standpoint, somewhere around about 20% is the maximum most profile wall thermoplstics can withstand without excessive wall strains.  However, in field applications, using 7.5% mandrel tesing seems reasonable.

Next point, most research shows that, in the ground, there is no long-term deflection lag.  In other words, the deflection after about 30 days is all the deflection the pipe will see.

All the discussion about pipe design, is difficult, if not impossible, to answer accurately for profile wall thermoplastics.  The interaction of the soil, the differing geometries of the profiles, residual stresses and myriad other factors make for a tremendously complex problem.  Most plastic pipe design theory is based on solid wall pipe(or worse yet, on elastic pipe theory like corrugated metal), not profile wall.  The design methods that do exist are not terribly effective at estimating in-field deflections.

Please see Chapter 6 of Highway Design Manual by McGraw-Hill where I spend considerable time discussing plastic pipe design. (plugging my contribution if no one minds)

As far as installation, sand can be utilized very effectively as pipe backfill, indeed, it can be better that #57 since the 57's usually do not fill the corrugation valleys very effectively, and are the "forced" into the valley after load is applied.  This typically results in some unavoidable pipe deflection.  What is critical is to what compactive effort was the sand placed?  If there was little to no compactive effort, consider yourself lucky that there wasn't even more deflection.  Sand backfill to 95% modified proctor should work.  

Now on to the actual question in the original posting.  There are ways to re-round thermoplastic pipe.  I would not recommend them.  Your real options are to either require the pipe to be excavated and relaid, accept a cost reduction, or require a service/maintenance warranty for some time period.  Since the specification required 5%, then that is what the contractor should have provided.

RE: PVC Pipe Deflection - Egging

With all due respect, I am concerned about possible long-term ramifications of some comments made on this thread.  If as some say a plastic pipe system is good for good long-term performance desired by an Owner even if short-term defection is far greater than 5%, why then have standards and a great many significant local specifications for many decades limit deflection??  Another reason for my skepticism was I once attended a paper/presentation many years ago where some researchers at least initially sort of lauded a very deep test installation (I think in Pennsylvania) of both corrugated and smooth-lined, profile-walled plastic pipes, and I believe then even postulated a theory that primarily inward compressive creeping behavior of the plastic (the pipe reportedly ended up being a smaller diameter than it started out!) helped to reduce the heavy earth load.  It appeared the intent of this paper (and I later found out similar papers by the same folks in multiple other engineering forums) was to promote some sort of rather high strain plastic/new design behavior phenomena, and I guess perhaps even thereby the use of similar plastic pipes for deep cover installations.  If I remember correctly, this particular test piping was VERY carefully bedded with very select materials and bedding/compaction was also VERY carefully inspected/tested, and I’ll note this pipeline at least short-term generally deflected LESS than 5%, I guess as a result of same.   
I subsequently also attended a paper/presentation of some competitive (not the same) researchers a few years later, who said that while the original researchers promised some longer-term follow-up of this installation the original reports, it was they instead who along with some other folks walked through this same piping installation just a few years later, inspected this installation, and they were thus reporting on the actual longer-term results.  They reported that while the line was not generally severely deflected, the line exhibited “several interesting conditions”, including:   “1.  Buckling of the inner liner of the smooth lined pipe.” And “2.  Circumferential cracking at the inside crest of the corrugated pipe.”  They noted that the various pipes in this installation apparently buckled in a couple different directions and/or manners, and they even described buckling as “severe”.  There was apparently cracking near every joint of pipe, at least one location not near a joint nor even under the deepest cover, and water was observed infiltrating the very carefully installed test line.  While I will note this test installation was of polyethylene pipe (normally most used for drainage), I am not sure exactly how any other similarly creeping plastics would be dependably insulated long-term from similar behaviors (and I also happened to notice above the reference/warning of “local buckling” also from stanier).  The newer authors also stated at the end of the newer paper, “Experience from other installations of polyethylene drainage pipe indicate that this type of buckling occurs at more normal depths.”  
With regard to the inference in posts that pipe deflections even up to 20% are from a theoretical standpoint somehow  acceptable, and while I can’t remember all specific details of problems, I am further very skeptical (even if a plastic pipe WALL happened to survive without long-term bucking or cracking) that all joints would maintain their integrity in a pipeline subject to such magnitude, unpredictable wall movements.  
With all due respect, and while I don’t doubt something close to this may have been accomplished in a controlled test installation somewhere, forgive me that I am also very skeptical of the general statement that in practice an installed, unpressurized gravity flexible plastic (subject to creep) pipe will all of a sudden simply stop deflecting say once it reaches 5% or 7.5% deflection in 30 days or less.  I believe this is contrary to some experience (and maybe even common sense!)  

While I guess I sort of understand the intent of after-the-fact sort of exculpatory statements that deflections far greater than 5% or 7.5% are acceptable (an attempt to help the parties at least initially sleep better, to prevent at least very early re-installation expense that must be borne by somebody, and/or at least initially prevent uncomfortable, embarrassing, and/or hostile contract disputes etc.??), in the long run I would nevertheless be very cautious based on what little I have seen/published to step outside this box/standard of care, lest one (as I heard a colleague of mine in forensic pipe work once say in perhaps a little of an overstatement, in referring I think to some similar very flexible pipe experiences) be in essence “burying their own Chernobyl”.  
I suspect some or all of the actual papers concerning what I am talking about in this post can probably be obtained/accessed by anyone for their own reading/consideration at nominal cost, through e.g. ASCE or other publications service with a keyword search.  I noticed also some time ago that are also some multiple interesting pictures of perhaps similar, apparently actual installed plastic pipe wall conditions now on the Caltrans site at http://www.dot.ca.gov/hq/oppd/dib/dib83-5.htm#5-1-4 (e.g. see Section “5.1.4 Plastic Pipe”).  
 If anyone cannot independently find what they want in this regard, I would be happy to try to dig out some more detailed reference information to help locate – please let me know on this thread if this is needed.                                

RE: PVC Pipe Deflection - Egging

I must respectfully disagree with rconnor in stating the long term creep of thermoplastics is common sense.  Reference is made to an extensive study by the Battelle Institute for the City of Columbus, Ohio in which the 30 day inspection recommendation is made. Further, work at Ohio University with thermoplastic pipe under 40 feet of cover also stabilized very rapidly.  This is the same experience generated by Ohio DOT in-house research.  The reason for this rapid stabilization is quite simple.  Under constant load viscoelastic materials will creep.  Under constant deformation they relieve themselves of stress (stress relaxation). This is the phenomenon exhibited in the PennDOT deep burial.  It is real.  When the side support of the soil is mobilized, the pipe exhibits circumferential shortening due to the load.  This shortening will create a positive soil arch and effectivly result in stress relaxation of the thermoplastic.  In the PennDOT study the measured stress at the crown of the pipe was approx. 30% of the free-field stress

I agree with rconnor that the limiting factor for pipe deflection is joint integrity not pipe performance. However, it is necessary to understand that the deflection limit is as much marketing as it is technical. It is also necessary to understand the ASTM process for developing standards.  This is a consensus specification authoring body.  If a specification can get enough positive votes it can pass.  This is not to say that bad information is generated by ASTM, on the contrary it is a great organization.  It is just information to better understand how the standards came to be.  The history of the deflection limit is tied to unibell pvc pipe and their desire to break into the sabitary market in the 40's.  At the time 15% deflection was deemed maximum for the pipe.  A factor of safety of 2 was applied, hence the 7.5% limit.  Since then, in an effort to introduce HDPE pipe to the market a deflection limit of 5% was proposed in order to be "better" than PVC.  Somewhere along the line, specifiers have been convinced that the 5% is a structural limit.

From a design standpoint neither deflection nor load alone can accuratley predict the pipe performance.  It is the strain derived from the combination of bending and compression.  A pipe with high deflection but low compressive stress may have a long life, while a pipe with low deflection and very high compressive stress may exhibit wall cracking and buckling.

In regards to the PennDOT study it is important to understand that the pipe in question, which I have personally seen, is under 100 feet of cover.  It was fully anticipated that the pipe would be highly distressed.  This was a goal of the study, to understand the limit state of the pipe.  Also, the orignial researchers authored a discussion on the second researchers work discrediting most of the conclusions.

The bottom line is that when installed well thermoplastics can perform well for a very long time.  If installed poorly, it will not.  Period.  As I said in my first post, this very well could be a never ending debate.  That said, I have offered my opinion based on 15-years of experience, almost exclusively with pipe mechanics, for the benefit of sewerratt.  I did not mean to open this can of worms.

If anyone is interested in any of the research I reference, please e-mail me.

RE: PVC Pipe Deflection - Egging

The problem with standards where it is by consensus is that plastics manufacturers see standards as a marketing tool. They invest heavily in getting members on committees to preserve and push their perspective. Some more aggressively than others. Government bodies and individuals can rarely provide the time( ie cost) to spend at committee meetings.

I am suspicious of any manufacturers claims as they do not provide guarantees.  They can always blame the contractor. You destroy the evidence when you exhume the pipe.

AS 2566 is written to provide a conservative design where the soil/embedment carries a large proportion of the load.

Lars Eric Janson has provided data supporting the deflection of pipes in the longer term. The problem with initial deflection (ovality) is that the soil is also oval and can thus deform more readily and buckle under external loads. If egging has taken place and the top soil is compacted then there is a tendency to square the corners of the pipe. This subjects the pipe to far higher strain rates that calculated for the oval of the egged pipe. This does result in failures at these corners.

RE: PVC Pipe Deflection - Egging

mrwhiteOH,
I guess we can agree to disagree that high compressive/bending/or whatever strains and deflections can be potentially injurious to the long-term integrity of systems such as discussed; however, I am not sure exactly how a specifying/inspecting engineer, Owner, or tax/rate payer for that matter are protected by such less unconservative opinion if/when? any one or more of these multiple bad things happens (particularly if it happens beyond say a one year contractor warrantee period).  We can also agree to disagree that as you apparently indicate there is some sort of magical quick stop to deflection, say within a 30 day time period; however, I believe much more notable folks than I, including a gentleman from my alma mater named Spangler (as early as 1941) and perhaps many others, including one Amster Howard et al have also found/taught (I think including crawl-thru examination of a great many installed actual flexible pipelines all over the place) that at least some movements (manifested also as increasing deflection) and as a result of relative soil/prism movements/natural consolidation etc., continues over a very LONG period of time. I believe they have also found/said this movement is generally more substantial when cohesive soils are involved than non-cohesive even when rather highly compacted, and there appears to be even some comparative data indicating that pipes like plastics move at least a little more than steel etc.  I suspect many other folks dealing with sewer pipes (normally deep) would probably also agree earth load can be rather heavy and unrelenting (and the pipe wall effects it influences)  over 50 or 100 years or so etc.!
With regard to your comment that the original researcher had "authored a discussion on the second researchers work discrediting most of the conclusions", I was not aware of this and hope at some point I get an opportunity to read this more recent work alongside the original.  It is obvious you are quite close to this situation, as you reported you had even seen this piping.  In this regard, could you please confirm at least whether or not the specific observations of the second researcher I thought I remembered/and repeated above are correct (in other words, did this short pipeline in fact develop over a period of apparently very few years many various cracks, buckles, and a leak etc. that as far as I know were not reported in the initial paper?)
Frankly, I do not remember from the original presentation I attended that they predicted piping would in any fashion fail or as you say comments to the effect, "It was fully anticipated that the pipe would be highly distressed...".  In fact, right or wrong I got the entirely opposite impression from the presentation I saw (I even assumed that some disbelief on the part of the second investigative group when they similarly heard of this pipeline and alleged load forgiving theory etc. may have sparked the competitors interest/decisions to go look at the installation themselves!)  As this was admittedly many years ago, I guess I will apologize upfront for any fuzzy memory or mischaracterization if what you say is true and not some attempt for whatever reason to re-write history.  I of course also did not state that joint concerns are "the" only ones with this pipe, just one among the others discussed.         
Some comments in above multiple posts related to these standards sadden me.  I personally think that what appears in standards or specifications for that matter should be reasonably understandable and generally also for performance/technical and practical manufacturing or measuring/testing etc. reasons, and while no standard nor piping material is perfect one would think that above all the intent of any business in it for the very long haul should be that the result will work in practical application (and not be part or centerpiece of some big marketing shell/blame game when there are problems)!  It makes one wonder also who is looking out for maybe now huge numbers of pipe specifiers/buyers who might not have the access or be able to afford the benefit/experience of either more critical/specialized engineering analyses (perhaps looking beyond the standards), nor armies of strong-willed jobsite inspectors to make sure even generally well-intentioned contractors spend adequate contract effort/money on the extremely high-quality construction that is apparently required for such pipes (and not on other things)?  Perhaps extreme levels of price competition between manufacturers, contractors, and maybe even engineering service providers could also be unhealthy. In any case, maybe there are reasons for/value of some "never ending debates".

"The bitter taste of poor quality remains long after the sweetness of low prices is forgotten."
 

RE: PVC Pipe Deflection - Egging

its poor instalation ,take the top off ,pack the sides and the pipe springs back up.

RE: PVC Pipe Deflection - Egging

Is it the product or the installation (or both)?

RE: PVC Pipe Deflection - Egging

Suffice it to say the piping product at least in this case did not have adequate effective stiffness to meet the installed specifications, at least with the initial installation conditions and inspection provided.  It would appear also that if all parties are not able to agree or work such matters out, any party with “deep pockets” (including those mentioned) might eventually be drawn in to the fray and the quality of expert witnesses and attorneys might then also be a factor!!  I suspect all would agree it is probably much smoother sailing if the pipe consistently meets the installed specifications with the prevalent quality of soil conditions, installation, and inspection etc.

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