波浪作用下可液化海床管线上浮失稳机理研究

    Study on the Mechanism of Uplift Instability of Pipelines on Liquefiable Seabed Under Wave Action

    • 摘要: 周围可液化海床的流场变化对于海底管线的动力稳定性具有重要影响。分别采用RANS方程和Biot动力固结方程描述海水运动(波浪)和海床内部孔隙流体运动。基于扩展Masing法则,构造了能够模拟可液化海床循环软化及循环流动大变形的黏弹塑性本构模型。通过在海水-海床交界面进行动水压力的实时传递,建立了波浪-海床–管线相互作用集成数值模型,模拟了Sumer等的波浪水槽试验以验证模型的可靠性。以金七门海域的典型钻孔作为场地条件,对波浪长期作用下管线的动力响应进行了数值分析。结果表明:(1)管线的存在改变了海床液化区域的空间分布,海床表面以及管线下部土体率先液化,后续液化区域沿着管线外壁向上演化;(2)近场偏应力减小速率较远场更为显著,管线周围产生大量的应变集中,同时其循环剪应力比CSSR相较远场更大,共同导致近场液化速度快于远场;(3)强烈的海床-管线相互作用加剧了近场海床的液化深度与范围,导致管线所受浮力增大与摩阻力减小,同时位于影响区内土体的塑性流动使得土体向管线底部聚集并挤压,共同导致了管线的上浮与侧移。

       

      Abstract: The changes in the flow field around a liquefiable seabed have significant implications for the dynamic stability of subsea pipelines. The motion of seawater (waves) and the pore fluid within the seabed is described using the RANS (Reynolds-Averaged Navier-Stokes) equations and Biot's dynamic consolidation equation, respectively. Based on the extended Masing rule, a visco-elastoplastic constitutive model capable of simulating cyclic softening and large deformation due to liquefaction of the seabed was constructed. By implementing real-time transfer of hydrodynamic pressure at the seawater-seabed interface, an integrated numerical model for wave-seabed-pipeline interaction was established. This model simulated Sumer et al.'s wave flume experiments to verify its reliability. Using a typical borehole from the Jinqimen area as site conditions, numerical analysis was conducted on the dynamic response of pipelines under long-term wave action. The results show that: (1) The presence of pipelines alters the spatial distribution of liquefied zones in the seabed. Liquefaction initiates at the seabed surface and beneath the pipeline, with subsequent liquefied areas evolving upwards along the outer walls of the pipeline; (2) The rate of reduction in shear stress is more pronounced in the near-field compared to the far-field, leading to significant strain concentration around the pipeline. Additionally, the cyclic shear stress ratio (CSSR) near the pipeline is higher than in the far-field, resulting in faster liquefaction rates in the near-field; (3) Intense seabed-pipeline interactions exacerbate the depth and extent of liquefaction in the near-field seabed, increasing buoyancy forces on the pipeline while reducing frictional resistance. Plastic flow of soil within the affected zone causes soil accumulation and compression under the pipeline, collectively leading to pipeline uplift and lateral displacement.

       

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