基于柔性边界模型的南海北部陆坡峡谷区海底滑坡运动定量研究

There is a risk of slope failure in the canyon area of the northern continental slope of the South China Sea. So, quantitative research of mass movement of submarine landslide in this region is of great significance for the assessment of landslide impact on the pipeline of Liwan3-1 gas field, since the pipeline has been laid along the canyon. The present research basically adopted a rigid bottom boundary in their model which can’t take account of the effect of soft seabed. Considering the very low strength of the seabed in canyon area, a numerical model scheme with soft seabed boundary condition is designed firstly for the landside mass movement based on Euler-Euler multi-phase flow theory in this study. Then, the small scale flume experiments with different bottom boundary, a hard rigid bottom case and several soft bottom cases with different shear strength, are performed. The rationality of the numerical simulation scheme and the accuracy of the numerical model are verified based on the experiment results. Then following the validated simulation scheme, a two- dimensional numerical back calculation model is established on the basis of the identification parameters of typical historical landslide, and the effect of seabed with different shear strength on the mass movement of the actual submarine landside is studied. Finally, three-dimensional numerical models are established according to the approximate recovery spatial models of submarine landslides in the study area. The movement process of sliding soil such as sedimentation, erosion and transportation can be obtained quantitatively, which shows the coupling mechanism between submarine landslides and the seabed. The study can provide a more accurate run-out prediction of landslide soil for the submarine pipeline design as well as the assessment of submarine landslide hazard, in the canyon area of the northern continental slope of the South China Sea.

南海北部陆坡荔湾3-1气田输气管道穿过的峡谷区，存在发生海底滑坡的风险，开展滑坡后土体运动的定量研究对准确评估滑坡体对管道的冲击影响十分重要。目前研究采用的刚性基底假设，不能反映松软海床的影响。本项目针对峡谷区底质较软的特性，首先设计基于欧拉-欧拉多相流理论的柔性海床边界条件下的滑坡土体运动模型方案，然后开展硬质刚性基底和不同强度柔性基底的小型水槽滑坡试验，并基于试验结果对数值模拟方案的合理性和模型的准确性进行验证；在此基础上，根据典型历史滑坡的识别参数，建立基于柔性边界的二维数值反分析模型，对比研究不同抗剪强度海床对实际滑坡体运动的影响规律。最后，建立基于地层恢复的三维空间滑坡数值模型，定量研究峡谷区复杂地形条件下滑坡体的沉积、侵蚀、搬运过程，揭示滑动土体与海床的动态耦合机制。本项目研究可以为南海北部陆坡峡谷区管道设计及海底滑坡地质灾害的评估提供更加准确的滑坡土体运动状态预测。

南海北部陆坡神狐海域峡谷区矿产资源丰富，但同时该海域海底滑坡地质灾害发育，给海底管线等设施安全带来较大威胁。目前海底滑坡模拟预测模型多采用刚性基底假设，不能较好反映松软海床与滑坡体的相关作用。针对这一问题，课题首先设计开展了多组硬质基底与柔性基底组合下的海底滑坡小型水槽试验，研究分析不同基底类型下滑动过程及特征，捕捉到滑坡体端部的滑水现象以及滑坡体引起的海床孔压升高现象，并观测到端部滑水时对海床影响较小，端部之后无滑水部分可以对海床造成侵蚀。结合研究目标区典型历史滑坡的识别参数，选择典型滑坡建立实际大尺度海底滑坡滑动模拟模型。模型基于欧拉欧拉多相流理论，考虑滑坡体、环境水以及柔性海床边界的耦合作用，设计了两种滑坡模拟方案。在相关数值方案模型验证的基础上，通过多组工况的模拟计算，研究分析柔性模型边界条件下滑坡体的动态特征与规律以及不同基底边界条件对实际海底滑坡运动的影响。同时对两种模拟方案的优缺点和适用性进行了对比分析，为后续相关研究提供参考。最后，以研究区海底峡谷侧壁识别出的典型滑坡为例，建立基于地层恢复的三维空间滑坡数值模型，定量分析了研究峡谷区复杂地形条件下滑坡体的沉积搬运过程规律。课题在执行过程中，为了考虑包含复杂转变过程类型的海底滑坡，完善课题研究内容，在原有研究计划的基础上，进一步增加了海底滑坡体引发的浊流动态过程模拟，研究分析浊流与海床的相互作用机制。研究成果可以为我国深水陆坡区海底滑坡地质灾害定量评价与防治提供一定程度的参考。