Does pipe stiffness greatly affect the level of deflection?
The pipe stiffness has only limited effect provided the level of compaction of the surrounding soil is good.
- The above statement is based on the findings of the TEPPFA Project on the Design of Buried Thermoplastic Pipes.
- This extensive field based project involved the controlled installation of plastic sewer pipes of various materials and stiffness classes.
- Pipes were installed in different soils with varying levels of compaction.
- In all, 16 pipelines each between 10 and 25 metres long were installed with different combinations of pipe material, pipe stiffness class, bed & surround material, native soil and level of compaction of backfill.
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Other conclusions from the Buried Pipe Project include :
- No failures were encountered even though some pipelines were installed in an extremely poor way.
- The quality of pipeline installation and good workmanship is by far the most influential factor with regard to the level of deflection of the pipe.
- Depth of cover is not an important influence on pipe deflection.
- Traffic load has no significant effect on final pipe deflection.
- The creep ratio is not important for the determination of the deflection.
- A good pipe deflection prediction can be obtained by use of a simple design graph which is based on extensive data of field measurements collected over the last 40 years.
- Deflection calculation methods are load driven and generally tend to over estimate the level of deflection.
- Based on experience PrCEN/TR15223 table 12 provides guidance for allowable maximum deflections at short and long term.
Want to know more?
Go to the Civils section of the TEPPFA website where you can access the full report on the Buried Pipe Project.
Refer to PrCEN/TR15233.
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