Pipe-sediment interaction of unburied marine pipelines on soft marine sediments

Abstract

Unburied submarine pipelines resting on soft marine sediments tend to embed themselves into the sediment when subjected to periodic hydrodynamic loading, provided a small amplitude of lateral movement of the pipe is allowed. The result of the pipe selfembedment leads to a substantial increase in pipeline stability against lateral movements. Therefore, it is believed that the lateral stability of unburied pipelines is dependent on the prior loading history. If this pipe-sediment interaction is properly modeled, it can result in a safer and more economical design for unburied submarine pipelines resting on soft marine sediments. A pipe-sediment interaction model is developed to determine the depth of pipe selfembedment and the corresponding ultimate lateral soil resistance. The prediction of the depth of pipe self-embedment was developed, empirically, through dimensional analysis and results of 57 cyclic displacement-controlled experiments. Theoretical and numerical procedures were used to determine the corresponding ultimate lateral soil resistance when the final depth of pipe self-embedment was known. The experimental results showed good agreement with theory if the effect of velocity on the undrained shear strength of the sediment was considered. The empirical portion of this model is valid for pipelines resting on sediment with natural water content lower than its liquid limit. Recommendations for using this pipesediment interaction model are included.