波致海床液化诱发黄河口异重流研究

Hyperpycnal flow is a kind of transport process of high-density sediment in the ocean, which has drawn increasing scholars' attention since that was observed in situ off the Yellow River estuary in the 1980s. Most researches maintain that hyperpycnal flow in the Yellow River estuary is caused by the high-concentration sediments discharged from the Yellow River into sea, while this project proposes that wave-induced seabed liquefaction can be one of the most important formation mechanisms. In order to verify and quantify the contribution of wave-induced liquefaction on hyperpycnal flow, this project involves three aspects of contents: 1) the meteorological, hydrological, and geological conditions and hyperpycnal features on the development of Yellow River hyperpycnal flows; 2) the variations of the stable seabed sediment in its property and state charateristics, and the influencing or controlling factors on transformation to hyperpycnal flow; 3) the quantitative description method for determinating the process that seabed sediment is liquefied and converted into hyperpycnal flow under multiple hydrodynamic conditions. In the implementation plan, hyperpycnal flow cases off the Yellow River estuary are collected and referred to analyze the river net inflows, sediment concentration and particle size, weather conditions, marine hydrodynamic conditions, and seabed sediment properties; physical modelling experiments are conducted on the Yellow River estuarine intertidal flat, and sediment samples are collected to perform laboratory dynamic triaxial tests and flume experiments; and numerical calculation is finally proceeded basing on the experimental data to analyze the formation process of hyperpycnal flow caused by the wave-induced liquefaction. The achievements obtained in this project can improve the understanding of the hyperpycnal flow formation and mechanism, and provide guidance on the prediction and control of subsea geological hazards.

异重流是海洋中一种高密度泥沙运移现象，自1980年代在黄河口发现以来，日益受到学者关注。已有研究认为，黄河口异重流形成是河流入海携带的高浓度泥沙所致。本项目提出，波致海床液化是导致黄河口异重流发生的重要成因之一。研究内容包括：1)黄河口异重流发生时的气象、水文、地质条件及异重流特征如何；2)已具有一定强度的海底沉积物，在发生液化并向异重流转化过程中，性态特征如何变化，以及哪些因素发挥影响或控制作用；3)如何定量判定海床土在何种条件组合下会液化转化成异重流。研究方法：搜集黄河口异重流案例，分析异重流发生时对应的河口入海径流量、泥沙含量与粒径、气象条件、海洋水动力条件、海床土性质；在黄河口潮滩开展模拟试验，并采集样品，进行室内动三轴试验与水槽试验；基于试验数据进行数值计算，模拟分析波致液化诱发异重流过程。研究成果对深入认识黄河口异重流的成因机制具有重要科学意义，对海底地质灾害预防具有指导意义。

黄河口异重流现象自1980年代被首次发现以来，一直是国内外学者关注的热点问题。已有研究认为，黄河口异重流形成是河流入海携带的高浓度泥沙所致，而近年来在气候变化和人类活动影响下，黄河入海泥沙量骤减，远小于异重流形成的临界值。本项目提出，波致海床液化是导致黄河口异重流发生的另一重要成因。利用现场观测试验、室内模拟实验与理论计算分析方法，系统研究了黄河口异重流发生条件与特征、黄河口已固结海床性态的波致液化特征及向异重流转化过程与影响因素、海床土液化导致异重流发生的定量判定方法。结果揭示了阵发性的强风浪作用下海床液化显著控制该海域的再悬浮输运量，并促使再悬浮沉积物向异重流转化；海床浅表层的液化可显著增加表层剪切再悬浮量，而深部残余孔压峰值区能量的缓慢释放所引起的累积渗流携带土颗粒上输泵送，同样诱发异重流的生成，这一过程受水动力、海床渗透性、固结度以及沉积历史的共同影响；在传统幂率剪切侵蚀再悬浮计算模型基础上，构建了波致海床液化导致内部沉积物泵送再悬浮的参数化模型，并计算得到黄河口埕岛海域再悬浮量可达黄河入海泥沙量的4-6倍，满足异重流发育的临界条件。研究成果在国际SCI期刊及国内核心期刊共发表学术论文22篇，其中SCI源刊收录7篇，EI源刊收录3篇；申请发明专利8项，其中获授权6项；有1名博士研究生、1名硕士研究生、4名学士本科生就本项目研究撰写学位论文；先后6次在国内外具有重要影响的学术会议上做口头演讲报告，其中做大会特邀报告1次；获科研奖励3项。研究成果对深入认识黄河口异重流的成因机制具有重要科学意义，对胜利埕岛油田海底地质灾害预防具有指导意义。