ABSTRACT
With the increasing development and utilization of offshore oil and gas resources, seabed instability around pipelines subject to combined wave and current loading is becoming increasingly important. Workable and efficient protection methods for offshore pipelines are desired by coastal engineers. As a continuation and extension of last chapter, the dynamic seabed response and liquefaction in the vicinity of marine pipelines under the regular wave loading and oblique currents are investigated. Two types of protection measures for subsea pipelines are presented, including trench layer for pipeline and Articulated Concrete Mattresses (ACMs). Based on the numerical results, we propose some design graphs for the critical backfill thickness of trenched pipelines by utilizing different backfill materials, as well as for the residual liquefaction when designing pipelines in a trench layer. In addition, we examine the foundation stability of deep-water pipelines under another protection countermeasure with Articulated Concrete Mattresses (ACMs). The studies show that the ACMs have a significant positive effect on preventing seabed liquefaction around the pipeline by pushing the liquefaction zone to both side of the shaft.
