Rate effects on the uplift capacity of pipelines embedded in clay: Finite element modelling

This paper describes a finite element study of the uplift behaviour of a plane strain pipe segment embedded in modified Cam clay soil. The primary aim of this study is to explore the role of rate effects on pipe uplift capacity and the transition between drained and undrained behaviour using coupled-consolidation analyses. The velocities considered in the modelling cover six orders of magnitude allowing a rigorous assessment of the effect of loading rate. The effects of pipe embedment depth, soil strength profile and pipe-soil interface roughness are also investigated. The results indicate that the range of uplift velocities for which the soil response can be considered ‘partially drained’, as determined from the peak uplift resistances, is significant and exceeds bounds established for full flow penetrometers previously reported in the literature. The data also suggests that excess pore pressures determined locally at the pipe-soil interface may not be a reliable means of determining whether the overall response is ‘drained’ or ‘undrained’. To address some limitations associated with design guidelines currently used by industry, a new approach for the prediction of pipe uplift capacity as a function of loading rate is proposed and applied to a hypothetical design scenario.