砂质海床上海底管道侧向失稳试验研究

Experimental study on lateral instability of submarine pipelines in sandy seabed

[目的]海洋环境具有复杂性及不可预测性,敷设于砂质海床上的海底管道易发生侧向失稳,但目前对海底管道侧向失稳的成因尚不明晰,亟需探究海流荷载作用下砂质海床上管道侧向失稳过程中的水动力荷载、管土相互作用等多种影响因素的耦合机制。[方法]采用自主设计搭建的机械加载试验装置开展多类型模型试验,在管道两端防止滚动与自由运动两种约束条件下,探究海底管道侧向失稳的物理机制,分析海底管道水下重力、管土摩擦因数、管道初始嵌入深度比、不同砂质土壤、端部约束条件等对极限侧向土阻力、侧向土阻力系数的影响。[结果]侧向土阻力随海底管道水平位移的增加而逐渐增大,并最终达到极限值;侧向土阻力系数随管道水下重力的增加而逐渐减小,最终趋于稳定值;防滚管道的侧向土阻力系数随摩擦因数的增大而增大,自由管道的摩擦因数对侧向土阻力系数的影响较小;防滚管道的侧向土阻力系数远大于管道两端自由的工况;防滚管道的初始嵌入深度比对管道出现最大沉降量及发生极限侧向土阻力的位置具有重要影响。[结论]海流作用下的管土相互作用是海流-管道-海床之间的动力耦合,明确了海流荷载作用下管道侧向失稳过程中极限侧向土阻力发展规律,可为海底管道的设计、敷设及安全运行提供技术支撑。(图11,表1,参31)

[Objective]In complex and unpredictable marine settings,submarine pipelines laid in sandy seabeds are susceptible to lateral instability.Nonetheless,the reasons behind this remain ambiguous.Consequently,investigating the coupling mechanisms of various influencing factors that contribute to the lateral instability process of these pipelines under ocean current loads becomes crucial,encompassing hydrodynamic loads and pipeline-soil interactions.[Methods]Multi-type model experiments were conducted,using the independently designed mechanical loading experimental setups that included two constraint conditions to respectively prevent pipeline rolling and allow free movement at both ends.The experimental results were leveraged to delve into the physical mechanisms behind the lateral instability of submarine pipelines.Additionally,an analysis was conducted to reveal the impacts of a range of factors on the ultimate lateral soil resistance exerted on these pipelines and the lateral soil resistance coefficient,including underwater gravity,the pipeline-soil friction coefficient,the initial embedment depth ratio of pipelines,various types of sandy soils,and the end constraints applied to the submarine pipelines.[Results]The lateral soil resistance was observed to gradually increase until reaching its peak,as the horizontal displacement of the pipeline expanded.Correspondingly,the lateral soil resistance coefficient decreased gradually stabilized ultimately,with the pipeline experiencing increasing underwater gravity.The lateral soil resistance coefficient of the anti-rolling pipeline rose with higher friction factors.In contrast,the friction factor had minimal impact on the lateral soil resistance coefficient of the pipeline in free movement.The lateral soil resistance coefficient of the anti-rolling pipeline significantly exceeded that of the pipeline with both ends free.The initial embedment depth ratio of the anti-rolling pipeline notably affected the maximum settlement and the location of ultimate lateral soil resistance.[Conclusion]The pipeline-soil interactions under ocean currents showcase the dynamic coupling involving ocean currents,pipelines,and seabeds.This paper elucidates the development law of ultimate lateral soil resistance throughout the lateral instability process of pipelines under ocean current loads.The findings offer technical insights to support the design,laying,and safe operation of submarine pipelines.(11 Figures,1 Table,31 References)