极端海况下南海岛礁地层防波堤动力灾变机理与分析方法

Islands and reefs are the most valuable land resources in the south China sea. In the south China sea, there are frequent typhoons, complex wave current conditions, and weak strata in the newly-built or expanded islands and reefs. Under extreme sea conditions, breakwaters may be damaged due to foundation instability, thus endangering the safety of the islands and reefs. In view of the reef formation wave in the structure of the dynamic disaster mechanism, this project intends to adopts theoretical analysis, numerical calculation and model test method to carry out the following research: research master reef structure characteristic and the typical terrain of the south China sea, analysis revealed nearly reef terrain abrupt change induced waves breaking process, as well as the strong nonlinear characteristics of wave slamming load; the typical stress path characteristics of the soil mass on the foundation of the wave proof building were studied. Based on the unit test, the dynamic constitutive model of calcareous sand considering the effect of particle breakage under complex loads was established. Based on sph-fem coupling technology, an integrated analysis model of wave-calcareous sand sea-floor and anti-wave building is established, and the key factors affecting the stability of breakwater in reef strata are analyzed and revealed. The research results of this project can be directly applied to the design and analysis of anti-wave structures in newly-built/expanded reef formations in the south China sea.

南海岛礁是我国南海最为宝贵的陆地资源，依托岛礁进行南海开发与建设意义重大。南海海域台风多发，波流条件复杂，且新建/扩建岛礁地层软弱，在极端海况下岛礁护岸防波堤可能因地基失稳发生损毁，进而危及岛礁安全。鉴于此，本项目拟联合采用理论分析、数值计算、模型试验等手段，针对岛礁地层中防波堤的动力灾变机理，依次开展以下研究：调研掌握我国南海岛礁典型地形与结构特征，分析揭示近岛礁地形陡变诱发的波浪破碎过程，以及波浪抨击荷载的强非线性特征；研究防波堤地基土体的典型应力路径特征，基于单元体试验建立考虑复杂荷载下颗粒破碎效应的钙质砂动力本构模型；基于SPH-FEM耦合技术，建立波浪-钙质砂海床-防波堤一体化分析模型，分析揭示影响岛礁地层中防波堤稳定性的关键因素，给出极端海况下防波堤安全设计的建议。本项目的研究成果可直接应用于我国南海新建/扩建岛礁地层中的防浪建筑物设计与分析。

吹填岛礁工程是我国建设海洋强国的重大战略措施，护岸防波堤作为吹填岛礁基础设施，肩负着抵御波浪掏蚀、维护吹填体完整的重任。南海海域台风多发，波流条件复杂，且新建/扩建岛礁地层软弱，在极端海况下岛礁护岸防波堤可能因地基失稳发生损毁，进而危及岛礁安全。本研究从海洋土力学角度出发，针对波浪作用下吹填岛礁钙质砂典型的力学特征以及应力路径，建立了能描述应力主轴连续旋转以及颗粒破碎的钙质砂动力本构模型，并给出了模型的标定方法。通过对钙质砂的单调和循环三轴试验以及空心圆柱扭剪试验结果的模拟验证了所提出本构模型的合理性。基于 Biot 动力固结理论及 VARANS 方程建立了波流-海床-结构物一体化数值模型。然后，基于欧拉显示积分算法将所研发的钙质砂动力本构模型嵌入一体化模型中。采用所建立的考虑应力主轴旋转及颗粒破碎效应一体化模型模拟了一系列水槽试验及钙质砂离心机振动台试验，数值结果与试验结果有较好的一致性，表明所研发的模型具有较高的可靠性。最后采用验证的模型研究了局部岛礁地层防波堤的水动力特性以及防波堤及其下方钙质砂海床在波流荷载联合作用下的动力响应特征。结果表明应力主轴的连续旋转以及钙质砂的颗粒破碎会加剧结构物周围尤其是结构物下方浅层海床中孔隙水压力的累积以及塑性变形的发展。这种影响会随着波浪作用周期的增加而愈发明显。位于防波堤下方海床厚度大约四分之一的钙质砂受颗粒破碎的影响最为显著，忽略钙质砂破碎的影响可能会导致孔隙水压力被低估 20% 以上。另外颗粒破碎对防波堤沉降的影响相较于水平位移更为显著，对防波堤下方海床塑性应变的影响相较于孔隙水压力更为明显。