Recommendations for determining nonlinear Winkler spring parameters for buried steel pipe stress analysis applications

Abstract

Abstract Permanent ground movements due to seismic fault rupture, ground subsidence or liquefaction-induced lateral spreading may result to failure of buried pipelines crossing the affected areas, due to the development of excessive bending and axial pipe strains. Verification of pipe integrity against such actions and design of mitigation measures is based on analyses with nonlinear beam-on-non-linear Winkler foundation models, where the soil reaction developing on a pipe as result of differential ground movements is modelled by means of elastoplastic springs. This note presents a new set of guidelines and expressions for determining the parameters of Winkler springs applicable to the analysis of steel pipes backfilled with sand and subjected to differential movement with a lateral, vertical-upwards and/or vertical-downwards component. The guidelines, collectively referred to as UoN recommendations, are accordingly employed in the parametric stress analysis of a buried steel pipe crossing an oblique seismic fault. Results of this parametric analysis demonstrate that adoption of the UoN recommendations in the analysis workflow results in considerably lower pipe axial and bending strains, compared to analyses based on current conservative methods, and thus more realistic and economical design solutions.