A buried pipeline is a system that takes into account both the properties of the pipe and the soil it is embedded in. Designers must consider the total structure of a buried pipeline to include the strength of both the pipe and the surrounding soil. Concrete pipe has significant structural advantages over flexible pipe.
With concrete pipe, the main structural strength is derived from the pipe itself. Designers simply determine the appropriate strength class of the pipe to suit expected loads.
Flexible pipe, such as plastic or metal pipe, has little inherent strength. The majority of the structural strength is provided by the surrounding soil. Engineers must predict the actual soil stiffness required and provide proper inspection throughout the construction process to ensure the soil envelope is made up to specification.
With rigid pipe, the structure arrives on the truck. During the construction process, flexible pipe structural strength is built by the installer and requires additional care by the contractor and designer.