Critical Review of the Creep Stiffness Test for Structured Wall Pipes

This paper, the first of a series on the subject, is a critical review of the creep stiffness tests performed on structured wall pipes in the UK. The review is timely in light of proposed changes to creep stiffness criteria, and associated test methods, and the imminent publication of a new specification for structured wall sewer pipes.

The conclusions raise fundamental questions regarding the validity of parallel-plate creep test methods in determining the structural fitness for purpose, in the contexts of the rationale of the test method, the mathematical characteristics of the data analysis and extrapolation, and the performance characteristics of the pipe-soil composite structure.

The dangers inherent in attempting to establish revised fitness for purpose criteria by correlating the stiffness results between the two different creep test methods are also highlighted. The conclusion is that the only sound basis for setting test criteria are engineering principles of fitness for purpose, as opposed to reacting to perceived problems, accepting historical criteria and attempting a straightforward data correlation between two fundamentally different test methods.