Session: 10-06-01 Pipelines and Cables

Paper Number: 120851

120851 - Experimental Investigation of the Cyclic Lateral Laying Effect on the Initial Embedment Depth of the Exposed Offshore Pipelines on Sands 

The initial embedment depth of the offshore exposed pipelines, which is mainly controlled by the soils and the loads caused during the installation, has a significant influence on the pipeline’s subsequent axial and lateral response governing the stability. However, engineering practices have shown that the initial embedment of the pipelines is often times higher than the predicted depth by using the recommended vertical penetration model. In this study, an experimental apparatus was designed to model the lateral cyclic motions caused by the pipe installation on the embedment of the pipeline on sands. The effects of the vertical forces, the amplitudes and frequencies of cyclic loads on both the smooth and the coating pipelines are investigated. The results show that the cyclic loads do cause the further significant embedment of the pipelines on sands but with a limit value, which means the ultimate embedment exists. The development of the embedment can be divided into three stages: the increasing stage, in which the embedment depth increases rapidly in the first 15 cycles and cause the 95% of the overall further embedment depth; the hypo-stable stage, in which the increasing rate is slowing down but still with an observed further penetration; the stable stage, in which the rate is decreased to almost zero and the ultimate embedment is reached. Meanwhile, the vertical force and the cyclic motion amplitudes cause a positive effect on the increase of the embedment, however, the frequency has a marginal effect.

Presenting Author: Cun Hu Research Institute of Tsinghua University in Shenzhen

Presenting Author Biography: Phd of Tianjin University
Research Fellow of NUS,
Professor in Research Institute of Tsinghua University in Shenzhen
Research Interests: Soil mechanics, offshore geotechnics, foundation-soil interaction modelling, offshore pipe line, suction bucket, plate anchor

Authors:

Hairong Xiong Offshore Oil Engineering Corp CNOOC Ltd.
Cun Hu Research Institute of Tsinghua University in Shenzhen
Ning He Offshore Oil Engineering Corp CNOOC Ltd.
Yang He Offshore Oil Engineering Corp CNOOC Ltd.
Ying Zhang Offshore Oil Engineering Corp CNOOC Ltd.
Ziqiang Ni Offshore Oil Engineering Corp CNOOC Ltd.