The equations and inputs used in calculating the pipe deflections using Australian Standard (AS 2566, 1998) ”Buried flexible pipelines” or similar standards have limitations. For example, standards convert a 3- dimensional wheel load to a simple 2- dimensional effect for calculation simplicity.  Compaction below and above the pipe haunch is different, yet simplified calculations use the same “embedment material” around the pipe.

Three-dimensional (3D) Finite Element Analysis (FEA) used in parallel with the AS2566 procedure showed similar deflections for simplified uniform ground conditions. Additional analysis scenarios using FEA and simulation analyses and not possible with closed form solutions are compared for specific pipe sizes, depths, pipe and ground stiffness. A few findings from such analyses will be presented.

The native soil modulus is the key factor using the current AS2566 prescribed values. Traditionally for low-height fills and small-diameter pipes the native soil modulus value used does not significantly affect a calculated deflection. As traffic live load, depth or pipe diameter increases, or shift to an extended design life, then these inconsistencies in AS 2566 become apparent.  An “error” in the native soil modulus values in AS2566 becomes evident.  Other inconsistencies with long-standing geotechnical standards are highlighted. Even various international standards and States seem to disagree on what should be basic input properties. Such inconsistencies in deign parameters adopted then require larger factors of safety in design to bridge such uncertainties.  This then impedes the wider use of the application of buried pipes.

Although not explicitly considered in the analysis, bedding may be one of the governing factors affecting the calculated deflection. Yet this is an assumed design value and an unknown in construction except for “standard” installation practices. Monte Carlo simulation analyses were also carried out to quantify such governing risk factors.