Good question. While I am admittedly not an expert on this subject, I am aware that some research and testing perhaps at least in part as you seek was done even long ago by some of the plastic pipe industry (I think back in the 1960's-1970's) and mentioned in an article, "Designing PVC Pipe for Water-Distribution Systems". This article was written by Mr. Robert Hucks (who I believe was then manager of a Johns-Manville research lab) and published in the July 1972 AWWA Journal. I noticed this article contained the statement, "Community-water-distribution systems require pipe that will perform without failure under the high flow rate and water hammer pressures created during fire-fighting activities." Under the paragraph, "Magnitude of Water Hammer Surges", the author said, "Initial work at the author's laboratory indicated that the pressure wave (water hammer) generated by rapid valve closure was greater in magnitude than that predicted by the Logan-Kerr equation (though how much greater was not revealed in this article). It appears the author’s company then “supported” perhaps a couple different research programs at Utah State University (USU) examining this subject. The first USU work, that apparently did not include any burial, reportedly concluded that the traditional equations, I guess at least when pipe actual modulus was considered, “accurately predict” surge, but they recommended further, buried condition work. Mr. Hucks then said per the subsequently performed work, with a rather shallow depth of “well-compacted” backfill (18 inches of cover?), “Preliminary results indicate the wave velocities are 7 per cent higher under buried conditions than for the previous study.” I believe he also mentioned that they felt axial restraint might be even more of a factor than radial in increasing pvc wave velocity/surge. [While not disclosed in the Hucks AWWA paper that included a graph of pressure vs. velocity changes up to only 8 fps, I read another report discussing the 1972 USU water hammer research on buried plastic pipe that interestingly reported in one run of valve closure at 10 fps flow velocity, one 6” PC160 DR26 pvc pipe was sort of inexplicably burst/split from one end to the other!, though an explanation for this failure was not disclosed in that report.]
Mr. Hucks also disclosed in the AWWA report the results of some “Field Studies of Operating Systems”, wherein researchers attempted to capture surges in three different (I assume actual) systems with pvc pipe. He reported based on “short-term measurements” the surge was 60 psi (20 psi above the steady state pressure) in the first system with “negligible elevation changes” and only some very small diameter pipe. In the second with up to 6” diameter pipe, reportedly supplied by three wells through “large hydropneumatic storage tanks”, he reported there was a 142 psi surge (102 psi over operating) with “rapid hydrant opening and closing”. In the third, with also up to 6” pipe, he reported a maximum of 162 psi surge (50 psi over a 112 psi operating pressure). In the third, he reported they subsequently took some “long-term measurements”, apparently revealing “pressure excursions” he said due to “high demand” to “225 psi approximately twelve times during the two-month period”. Mr. Hucks reported that the situation in the third case was considered serious enough to “advise the operators that PVC pipe failures could be expected within the next ten years without taking corrective steps.” Mr. Hucks also reported (but apparently not considered in the water-hammer research), “Since PVC pipe moves axially as well as circumferentially in response to pressure surges (“Poisson’s ratio effect”), pipe may undergo scratching of the outside when buried and in contact with sharp stones in the backfill. This area requires further study.”
I should probably also mention that the research referred to by Hucks involved “ASTM” specification pvc pipes, much of which is less stiff then contemporary AWWA specification pvc pipes.
In addition to stiff soil backfill, I think also all types of pipes are sometimes encased or partially encased in areas with concrete and/or flowable fill or grout encasement, and/or passing into and out of concrete etc. structures, and near inevitably plastic pipes are also connected at some point to stiffer pipes (such as steel or ductile iron piping), an effect that probably should also be considered by competent engineers in surge analyses. In addition to stiff soil backfill, I will note also all types of pipes are sometimes encased or partially encased in concrete and/or flowable fill or grout encasement, and/or passing into and out of concrete etc. structures, and near inevitably plastic pipes are also connected at some point to stiffer pipes (such as steel or ductile iron piping), an effect that probably should also be considered by competent engineers in surge analyses.
Interestingly, while the current 2002 AWWA Manual M23 manual for pvc pipe does include the statement, “The pipeline designer should be aware that the geometry and boundary conditions of many systems are complicated and require the use of refined techniques similar to those developed by Streeter and Wylie”, it appears to still advocate after all this that surge be determined by “elastic wave theory of surge analysis” (with a modulus of 400,000 psi assumed for the pipe, etc.) I believe some other authorities are advocating more conservative surge provisions for pipe selection. Perhaps there has been more recent water hammer research that covers more issues than that of Mr. Hucks – I will wait along with you to see. Sorry for the long post, but perhaps this reference and information will be helpful to you.
