Advances in Predicting Pipeline Embedment Based on Assessment of Field Data

摘要

This paper reviews the current methodology for assessing pipeline embedment against field data, whereembedment levels were under-predicted leading to an unconservative design. An updated model isprovided for predicting pipeline embedment. One important principle behind this new approach is todefine the operative soil strength, based on reconsolidation of the remoulded soil beneath the weight ofthe empty pipe during the intervening period between laying and flooding. This approach is based onpipeline embedment data from the field, which has demonstrated that soil around the pipe can becomefully remoulded during installation. Therefore, embedment in the flooded condition should be assessedusing an operative strength from reconsolidation, rather than the intact strength, which is current practice.This paper also provides current equations that improve the prediction of embedments over one-halfdiameter, by proposing methods to take account of the increasing buoyancy with depth, the reducinginfluence of heave mounds and modified penetration resistance at deeper embedments.Pipeline embedment is a fundamental input to the assessment of pipe-soil interaction, which is thelargest uncertainty faced in the design of pipelines subject to lateral buckling and walking phenomena.However, pipeline embedment is notoriously difficult to predict due to the inherent uncertainty of theinstallation process. Improving the prediction of pipeline embedment is critical to reducing the range ofpredicted pipe-soil responses in design.A current project has compared high quality observations of pipeline embedment from an earlier phaseof the same field development, against predicted embedments using more recent, high quality soils datafrom parallel pipeline routes, including fully remoulded soil strength from cyclic penetrometer testing.While current design approaches were under-predicting embedment levels, leading to a potentiallyunconservative design; this updated methodology provided a much-improved match to actual embedmentdata. The revised model was successfully verified against measured levels of pipeline embedment and isnow being used for the design of future pipelines in the area, with improved certainty and easing of thedesign challenge.Under-predicting pipeline embedment could be critical to design integrity. The methodology presentedin this paper has the potential to improve assessments of embedment and avoid unconservative pipe-soilresponses on future developments.