An investigation into pipelines subjected to lateral soil loading.

摘要

This thesis presents a research program conducted to examine one aspect of pipeline/soil interaction; that of lateral pipeline/soil interaction.;The objectives of the research program outlined in this thesis were to: (1) conduct physical model testing of lateral pipeline/soil interaction in cohesive soil to ascertain the effects of trench width, burial depth, interaction rate, backfill properties, and stress history of the soil on the interaction using the centrifuge technique to maintain similitude between model and full-scale; (2) determine the characteristics of normalized force-displacement curves or interaction factors so that they can be used generically; (3) assess the displacement patterns and failure mechanisms of the soil around a pipeline; and (4) generate conclusions and recommendations regarding current and proposed methods of analysing lateral pipeline/soil interaction through comparison with experimental results.;This thesis demonstrates that: (1) the trench width had little or no effect on an undrained interaction; (2) the undrained load on a pipeline increased with increasing burial depth; and (3) the pipeline displacement rate (and thus drainage conditions) had a significant effect on the loads transferred to the pipeline by the soil (for this particular soil/backfill system). The pipeline displacement rate effect is significant because the current state-of-practice for cohesive media is based on an undrained interaction between the pipeline and the soil which can significantly underestimate the ultimate load transferred to the pipeline. Also, the displacements required to reach these ultimate loads are significantly underestimated in existing guidelines for the soil/backfill system considered. Results from existing and proposed analysis methods to predict pipeline/soil interaction curves are encouraging.;The undrained force-displacement response could be reasonably predicted and ultimate loads can be predicted within +/-20% using existing methods of analysis. Experimentally derived methods of undrained analysis provided reasonable fit to the experimental data; an average of within 10% of the ultimate lateral load might be expected. Other potential methods based on undrained anchor/soil and pile/soil interaction resulted in predictions of ultimate loads within 20% of those measured experimentally. Pile/soil interaction p-y curves were found to provide reasonable predictions to the experimental data. Bearing capacity solutions showed potential to bound the actual ultimate load. Passive earth pressure solutions were found to yield reasonable undrained prediction for cases where the pipeline was shallow (H/D 2).;Predicted drained (c-&phis;) ultimate loads on the pipelines were consistently underestimated using existing methods. Drained analysis methods from the experimental data could be expected to predict the force-displacement response of the experimental data to within +/-20%. Drained anchor/soil interaction analysis methods underestimated the experimental data. Drained pile/soil interaction methods provided reasonable fits to the data in cases. Cohesionless soil p-y curves were found to overestimate the actual experimental force-displacement response. Cohesionless soil bearing capacity solutions were found to overestimate while passive earth pressure solutions tended to underestimate the ultimate lateral loads. (Abstract shortened by UMI.)