The choice of bedding design and standard of construction is as critical to the success of a pipeline installation as the choice of pipe. Understanding its importance, but not understanding the choices available, can lead to over-specification. Bedding design is one area where it is possible to prove the extent of this impact and the CPSA Structural Design and Material Cost calculators can play an important role.
There are a range of bedding solutions – or Classes – that are acceptable depending upon the material from which the drainage pipe has been manufactured, its strength and performance characteristics, traffic loading and the depth at which it is installed.
Bedding is particularly important for flexible pipes, such as sewer pipes manufactured from HDPE. This is because pipelines constructed with flexible pipes need to derive a significant proportion of their structural strength from the embedment either side of the pipeline to prevent them deflecting excessively under load, a condition known as ovalisation, where initially the vertical diameter of the pipe reduces and the horizontal diameter increases.
As a consequence of their lack of inherent strength, flexible pipe installations depend heavily on a high quality installation where the construction is carried out precisely to the engineer’s specification where the surrounding embedment takes the majority of the pipeline’s designed loading.
To help make the options more transparent, CPSA has developed a web-based Structural Design Calculator tool to help with the selection of appropriate bedding Classes for buried pipelines and a second tool – the Material Cost Calculator – to enable a clear cost comparison of different solutions.
Using these calculators recently allowed Leeds based ground worker and civil engineer Athena Civil Engineering to take the initiative on a new housing development in Roundhay near Leeds.
Using the CPSA Structural Design and Material Cost calculators, Athena was able to determine the optimum bedding design for the project. Consideration was also given to the excavated material from the trench, which was deemed suitable for backfill purposes.