DESIGN OF LARGE DIAMETER BURIED PIPES

Papers # 2018 Las-Vegas

The behavior of buried plastic pipes is already well described in standards and technical specifications and as well as proven in real life conditions. Plastics pipes in diameters up to around 400 mm are already in use for more than 60 years and pipes with larger diameters for more than 20 years now. All with good experience. However, the pipe market is conservative and the advantages of flexibility in especially large diameter buried pipes are still not recognized in all countries. This study brings more evidence and will help to an even broader acceptance of the use of plastic pipes – especially in large diameters.

In the late nineties TEPPFA carried out a study into the behavior of buried thermoplastics pipes. The project had input and participants from both the Plastic Pipe industry as well as from external organizations. Six external leading experts in the field of pipeline design, not necessarily plastics pipes design, have been involved as consultants in the project. The experimental work included a number of less ideal installation circumstances, in order to fully understand where the border line of safe installations is by predicting the performance of the buried pipes. Parameters, like depth of cover, pipe stiffness, installation quality and pipe material’s creep ratio have been studied. 

A report that summarized the experimental work carried out was issued including an analysis of the pipe soil interaction process as it was monitored during the study. Next to that a simple design graph explaining the short and long-term deflection as a function of the pipe stiffness class and the quality of the installation. The results have been presented at the Plastic Pipe Conference /3/, /4/ and in magazines /5/ as well as it is being used in standardization work, e.g. in developing CEN TS15223, “Validated design parameters of buried thermoplastics piping systems”.

Although the physical rules stay the same the world has changed. The need for water tight solutions in large diameter drainage and sewer pipes has given plastic pipe solutions a significant increase in market share in Europe, very well supported by the introduction of the EN 13476 standard which describes a number of different ways to design and produce a structured-wall pipe. TEPPFA has therefore decided to extend that Buried Pipe Study by adding field test and measurements of large diameter structured wall pipes in order to enhance the scope and the validity of the earlier results to those bigger diameters. With the knowledge from the earlier TEPPFA project, in which it was shown that the material’s creep ratio is not an important parameter, it was decided to do all tests with PE structuredwall pipe because of its availability at the site.

A test in Denmark has been executed and SN2 and SN4 PE pipes according to EN13476 has been installed under “Good”, “Moderate” and “Poor” conditions. The soil used has been poorly graded sand / silt mixtures which allows the poor installation. If a rather freefloating uniform backfill would have been used, it would be difficult to create poor installations. The deflection has been measured after assembly but before backfilling and then again after backfilling and completion of the installation. Measurement has been repeated after 10 weeks and 19 weeks. It is planned to continue measuring according the results observed. An older test installation in Finland on the property of Uponor in Vaasa has been included in the project as well. This test installation is affected by severe traffic load.

Related keywords : Buried Pipes, Installation, Compaction, Defection, Stiffness Class, Traffic load.
Please note that the whole article content is available on PPCA website onlySource : 2018 Las-Vegas


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