Theme Lecture – Recommendations for determining Winkler spring parameters for pipe stress analysis applications
G. Kouretzis, Associate Professor, School of Engineering, University of Newcastle, Australia
Buried pipelines crossing seismic faults, subsidence zones, or areas susceptible to liquefaction-induced lateral spreading are designed to accommodate differential ground movements without developing excessive bending and axial strains, frequently by implementing special mitigation measures. This requires performing nonlinear numerical analyses with general purpose or specialised finite element software, where the soil reaction developing on the pipe as result of differential movements is modelled by means of elastoplastic Winkler springs. State-of-practice methods for determining the parameters of such springs are based on physical model tests performed in the 1980’s or on (over-)simplified analytical solutions. This talk will introduce a new generation of guidelines and expressions for determining the parameters of Winkler springs required to model pipes in sand, subjected to differential movement with a lateral, vertical-upwards and/or vertical-downwards component. The guidelines, collectively referred to as UoN recommendations, are based on the results of a series of physical model tests, performed to document the mechanics of sand-pipe interaction during differential movement episodes, considering pipes embedded at a wide range of depths in loose to very dense uniform sand. The UoN recommendations cover certain important gaps in current practice, by accounting for the effect of stress level dependence on the reaction force on the pipe, or the variation of the shape of the failure mechanism developing around the pipe with sand density and embedment depth. They also allow rigorous estimates of the reaction force associated with vertical-downwards movements, which is critical for most ground movement scenarios. The presentation will conclude with example applications, demonstrating the use of the UoN recommendations in pipeline engineering practice.
Keywords: pipelines; soil-pipe interaction; physical modelling;