基于波致动力固结的黄河三角洲铁板砂形成过程研究

Consolidated silt is widely developed in the Yellow River delta, which threatens the security of offshore facilities such as platforms and pipelines, as well as shipping. The recent formation modes of consolidated silt such as primary sedimentary, residual coarsening and wave-induced liquefaction reform, which were mainly based on qualitative analysis and speculation. While the forming process, particularly the physical and mechanical behaviors during the process are not clearly described. In this project, the perspective of wave-induced seabed consolidation is adopted, laboratory simulated tests including wave flume tests and sediment column tests are carried out to investigate the dynamic consolidated process of saturated silt seabed under wave loads, in which the consolidated mode and consolidated rate under different wave conditions are particularly explored; the coupling effects of stress flied, , displacement field and seepage field in the seabed, and the sediment dynamics and bed surface change at seabed surface are investigated. The formation mode of wave-induced dynamic consolidation of consolidated silt is proposed accordingly. Based on Biot’s consolidation equations, the physical and mechanical model for the forming process of consolidated silt in the Yellow River delta is established, and is solved with finite element methods. Research results on this project will promote the understanding of forming process of consolidated silt, enrich the theories and methods of marine engineering geology, and provide technical support for offshore engineering and shipping in the Yellow River delta.

黄河三角洲广泛发育由粉土构成的铁板砂，严重威胁平台、管线等海洋工程安全及航运安全。现有的原生沉积、残留粗化、波浪液化改造等铁板砂形成模式多基于定性分析和推测，而对铁板砂形成过程及其物理、力学行为的定量描述存在不足。本项目拟从波浪作用下海床动力固结的角度出发，开展水槽试验和土柱试验等室内模拟试验，研究常规波浪及风暴浪作用下粉土海床动力固结过程，着重探究不同波浪条件下海床固结方式和固结速率，揭示动力固结过程中床内应力场、位移场、渗流场和床面泥沙运动、床面位置变动等床内-床面耦合机制，提出基于波致海床动力固结的铁板砂形成模式。以Biot动力固结方程为基础，构建黄河三角洲铁板砂形成过程的物理、力学模型，并采用有限元法实现模型的计算、求解。研究成果将增进对铁板砂形成过程的认知，丰富海洋工程地质理论方法，为黄河三角洲地区海洋工程建设和航运保障提供技术支持。

铁板砂是一种特殊的海底动力地貌，主要以沉积物硬壳层的形式发育于海底浅表。铁板砂在我国河口、海岸和近海广泛发育，其分布和特征主要由海洋水动力与海床的相互作用所控制。本项目以铁板砂形成和演化过程的物理机制和定量评价预测为科学目标，从海洋土力学与沉积动力学相结合的思路出发，通过开展黄河三角洲天然潮滩开展现场试验、饱和粉土海床孔隙水及细颗粒物质渗流失踪和定量测定试验、文献调研和分析、饱和粉土声传播规律实验研究、现有水槽试验结果的再分析、基于Biot理论的铁板砂定量评价预测理论模型开发等工作，实现了对波浪作用下海床表面附近的沉积物起动、悬浮、沉降以及海床内部孔隙水压力升高、液化、渗流、固结等物理过程的详细描述和清晰刻画，增进了对铁板砂形成和演化过程的认知，通过表征冲刷和液化对沉积物在悬浮贡献并实现定量计算，实现了对铁板砂形成和演化过程的定量评价和预测。并在此过程中，揭示了黄河三角洲潮滩微地貌与铁板砂分布和性质的内在联系，提出了粉土海床细颗粒物质垂向渗流的有效测量方法，探索了不同固结状态粉土在固结和剪切过程中压缩波速变化规律，建立了考虑波致海床液化的海上风电单桩基础水平变形评价、海底目标物下沉评价方法。本项目从铁板砂形成演化的物理机制到定量评价预测、科学揭示铁板砂形成和演化过程，再到具体应用、为海洋地质灾害防治与海洋工程建设提供参考与支持。