Plastic Pipes Conference Association # 2023 Lake Buena Vista
Anders Andtbacka, Peter Sejersen
In March 1999, a project report on the performance of buried Thermoplastics pipes was published by TEPPFA /1/. In the report, deflection and strain data on buried pipes were analyzed and compared with calculation results from several well-known static calculation models in use in Europe. Pipes were installed to different depths of cover, with different levels of compaction, and performance was monitored during traffic loading. The development of long-term deflection as a function of time from installation deflection, was also investigated.
Installation data was obtained on pipes with DN400, and the validity of the resulting design graph extends up to DN1100. Since the publication of this report, thermoplastics pipes of ever larger sizes have been introduced, and the need for an extension of the design approach has become evident. A second phase of the TEPPFA Buried Pipes project was initiated in 2017, with installation of DN1000 pipes in early 2018 /2/. Installation data was collected and compared with the original report. The new results were in expected alignment with the previous ones.
When developing a calculation method relevant for the extension of the design graph, it was recognized that critical loading cases will be the minimum depth of cover below dynamic loads and static loads other that the soil cover. Therefore, a set of conditions for the method were agreed /3/. These conditions include:
- The range of pipe diameters is between DN1100 and DN3000
- The depth of cover is 1.0 – 6.0m
- The embedment fill material around and up to a minimum of 0.15 m (or the value prescribed by local road authorities) above the top of the pipe shall be a granular soil, placed in shifts and compacted to a minimum of 90% modified Proctor.
- Pipes with a structured wall shall meet the requirements of EN13476, including the 30% ring flexibility requirement.
Some of the other conclusions in the first report were that calculation models are quite accurate for well-done installations. For poor installation cases, most methods had difficulties defining input values, which lead to both overestimation and underestimation of actual values. In all, the importance of correct information on soil data and workmanship were crucial to the accuracy of the deflection predictions.
Comparisons have now been made between measured dynamic deflection data of DN3000 thermoplastic pipes, the new calculation model and the so-called Gumbel method given in BS9295 /4/. Differences between calculated and measured data largely follow the pattern known from the original TEPPFA report.
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