深海粘性土边坡地震失稳演化机理及动力分析方法

Submarine landslides are widely distributed, difficult to identify and severely destructive. Submarine clayey slopes in the deep-sea continental slope area are more susceptible to instability under earthquake action, causing serious disasters to ocean oil and gas development projects and safety operations. Based on the investigation of typical structural clayey slopes on the earthquake-prone areas in the northern continental slope of the South China Sea, the geological engineering model is obtained through the generalization of the actual landslide or slope. Then the kinetic and computational mechanics models focused on large deformation are established for CEL method, as well as the CEL method should be redeveloped by introducing the dynamic shear modulus model that characterizes the microstructure evolution of clay. Simultaneously, the numerical simulation results of the whole dynamic evolution process of submarine clayey slope under seismic loading are reproduced and validated by large-scale underwater shaking table model tests, which are based on the combination of the fiber Bragg grating (FBG) and the particle image velocimetry (PIV) technology. In order to reveal the mechanisms of dynamic catastrophe process and the instability patterns, the dynamic stability of the submarine clayey slope and the evolution process of landslide with various main affecting factors, such as complex morphology and soil characteristics, marine environment, and ground motion parameters, etc. are simulated. In addition, various main controlling parameters are analyzed and contrasted comprehensively, then the relationships between each main parameter and slope dynamic response, pore pressure model, key point displacement, etc. are established. Furthermore, the practical criteria for earthquake-induced instability of deep-sea clayey slopes are put forward. The achievements of this research can provide scientific evidence for the prediction of submarine landslides in the deep-water continental slope of the South China Sea under seismic loading, the safety of oil and gas engineering, route selection, regional earthquake prevention and disaster reduction planning and countermeasures.

海底滑坡具有分布广、识别难、致灾重等特点，而深海陆坡区更易发生粘性土边坡地震滑坡，给深水油气开发工程和安全运营带来严重危害。针对地震多发的南海北部陆坡区，以典型结构性粘性土边坡为依托，概化工程地质模型，建立基于CEL方法的动力大变形计算力学模型；引入表征土体微结构演化特征的动剪切模量模式，发展海底边坡地震动力分析方法，模拟地震触发深海粘性土边坡动力失稳与大变形演化过程，并基于PIV与光纤光栅联合监测技术的大型水下振动台试验进行验证；系统模拟复杂形态与土层特征、海洋环境、地震动参数等主控因素下粘性土边坡动力稳定性与滑坡失稳演化过程，揭示其动力灾变机理和失稳模式；通过变动参数比较研究，建立各主控参数与边坡动力响应、孔压模式、关键点位移等相应关系，提出地震触发深海粘性土边坡失稳的实用性判据。成果为南海北部深水陆坡区海底地震滑坡预测、油气工程安全和路由选线、区域防震减灾规划和对策制定提供科学依据。

本项目基于“海洋强国”和“一带一路”重大战略需求，从南海北部大陆坡复杂地震地质环境下深海资源开发安全的现实背景出发，针对影响海底基础设施建设（如海上平台基础、海底管缆、水合物开采井等）及其安全运行的地震触发海底滑坡这一重大问题，采用海洋工程地质调查、室内与船载土工试验、理论分析、数值模拟和物理模型试验等多手段开展了针对性研究，全方位揭示了地震触发深海粘性土边坡失稳的动力灾变机理与滑坡演化规律。具体包括：开展了海洋软粘土动三轴试验，结合微观电镜和CT试验，发现了动力扰动过程中土体微结构演化特征，构建了海洋粘土动力模型并对模型参数进行标定；改进了CEL大变形数值方法，开展了地震荷载作用下深海粘性土边坡的动力稳定性、失稳机制和破坏模式研究，结合流固耦合数值方法，模拟了滑动失稳后滑坡体的运动过程和演化规律；结合海底斜坡地震稳定性分析，发展了区域尺度海底滑坡地质灾害易发性评估方法；进一步，开发了基于光纤传感和PIV监测技术的海底斜坡失稳及滑移过程的模拟水槽试验，揭示了复杂环境下海底边坡的失稳破坏机制和海底滑坡运移过程中的水—土界面质量输运机理，开发了相应数值模型并对其可靠性进行了检验；通过大量数值计算与变动参数研究，提出了海底滑坡冲击深水管线的简化分析方法和管线自防护技术。上述成果可为南海北部深水大陆坡地震触发海底滑坡预测、油气工程安全和管缆系统路由选线、水下基础设施防震减灾规划和对策制定提供科学依据。