A Designer’s Guide to Plastic Sewer Pipe Stiffness Classes 

Plastic sewer pipes are manufactured in a range of stiffness classes to allow designers to develop the optimum solution for different site conditions. TEPPFA has produced a new guide which aims to provide designers with useful information regarding the classes available, their characteristics and performance in order to assist with the selection of the appropriate stiffness class for a specific project.

Flexible sewer pipes are designed to work in conjunction with the surrounding soil. The extent of pipe deflection is governed primarily by the backfill compaction and the settlement of the soil in the pipe trench. When the trench backfill is fully consolidated, traffic and other loads do not have a further effect on pipe deflection.

Plastic sewer pipes were first manufactured with a solid wall construction and the pipe stiffness could be directly related to wall thickness. With the introduction of a range of European Product Standards for different types and configurations of plastic sewer pipes a standard test method for characterising the ring stiffness of flexible pipes was developed which can be applied across all types of plastics and pipe wall constructions.

Using the output from a major research project completed by TEPPFA some years ago an interactive tool has been developed which allows a quick assessment to be made of the extent of long term deformation. It uses a number of parameters including the pipe stiffness class, the assumed level of backfill compaction and pipe and trench dimensions.

The TEPPFA Guide contains detailed information on:

·      The performance and reliability of plastic sewers

·      Design and installation guidance

·      How stiffness classes are measured and specified

·      How to access the free TEPPFA interactive tool for assessing sewer pipe deformation

“The Designer’s Guide to Plastic Sewer Pipe Stiffness Classes” can be downloaded using the following link to the TEPPFA website.