极端波浪作用下岛礁防波堤动力灾变机理及生态减灾对策

The adequate utilization of ocean space for construction of offshore micro-reef is extremely important to the development of the marine economic of China. However, the breakwater around the artificial reef may suffer instability under the typhoon-induced extreme wave loading due to the degradation or failure of the calcareous sand seafloor. Firstly, based on the stress path of the typical soil element of the seabed beneath the breakwater under the typhoon-induced extreme wave loading, extensive experimental studies on the dynamic behavior of Paracel saturated calcareous sand are carried out. Subsequently, a dynamic constitutive model is proposed to describe the behavior of saturated calcareous sand, such as the particle breakage, principle stress axes rotation and cyclic degradation. Then, it is to be verified and improved by a model test. Secondly, a series of nonlinear dynamic analysis on the interaction between extreme wave loading and saturated calcareous sandy seabed and breakwater will be carried out to reveal the dynamic catastrophe mechanism of the breakwater subject to the typhoon-induced extreme wave loading. Furthermore, the corresponding model for evaluating the stability of the breakwater will be established. Finally, extensive experimental studies on the test of calcareous sand solidified by Microbial Induced Calcite Precipitation (MICP) are carried out. The validation of the calcareous sandy seabed solidified by MICP will be evaluated by model test and numerical simulation. Then, the ecological countermeasure based on the technology of calcareous sand solidified by MICP is proposed to resist the extreme wave loading. The achievements of this research will enrich and develop the constitutive theory of calcareous sand. Moreover, they will provide theoretical basis and technological support to the ecological construction and protection of the artificial reef.

充分利用海洋空间大力开展远洋微型岛礁建设，对于我国发展海洋经济意义重大。然而，在台风诱发极端波浪作用下人工岛礁防波堤可能因下卧饱和钙质砂海床的弱化或破坏而丧失稳定。本项目以西沙饱和钙质砂为研究对象，首先根据数值模拟确定极端海洋环境下防波堤下卧海床典型单元体的应力路径，基于此开展饱和钙质砂动力学性质试验，提出能描述颗粒破碎、主应力轴旋转、循环弱化等特征的饱和钙质砂动力本构模型，并通过模型试验对其验证和优化。然后开展极端波浪-饱和钙质砂海床-防波堤相互作用系统的非线性动力分析，揭示极端波浪作用下防波堤的动力灾变机理，提出防波堤稳定性评价模型。最后，开展MICP固化钙质砂的试验研究，通过模型试验和数值模拟验证MICP加固钙质砂海床在极端海洋环境下的固化效果，提出基于MICP固化钙质砂技术的生态减灾对策。研究成果将丰富和发展钙质砂动力本构理论，有望为生态岛礁建设与维护提供重要的科学依据和技术支撑。

充分利用海洋空间大力开展远洋微型岛礁建设，对于我国发展海洋经济意义重大。然而，在台风诱发极端波浪作用下人工岛礁防波堤可能因下卧饱和钙质砂海床的弱化或破坏而丧失稳定。本项目以西沙饱和钙质砂为研究对象，采用室内试验、理论分析和数值模拟相结合的方法，开展了不同相对密实度下饱和钙质砂一维压缩和直剪试验以及不同循环应力比、频率、周期、围压下饱和钙质砂动三轴试验，揭示了极端波浪作用下钙质砂动/静力响应特征，基于此，构建了饱和钙质砂动力本构计算模型，开展了风暴潮、堤前驻波、洋流等作用下波浪-海床-结构物相互作用数值模拟，揭示了极端海洋环境下海工结构的动力灾变机理。研制了一系列MICP固化钙质砂单元体制样仪，开展了MICP固化钙质室内单元体试验、微观试验及模型试验，提出了基于MICP固化钙质砂技术的生态减灾对策。与此同时，还构建了考虑扰动影响滨海砂土本构模型，基于改进响应面法开展了海堤边坡三维可靠性分析，研究了降雨入渗条件下非饱和多层海堤边坡最危险滑动面的确定方法，最后，研究了波浪与盾构施工耦合作用下软黏土的力学性状及其生态加固措施。本项目的研究成果丰富和发展了极端海况下滨海土体动力本构理论与加固技术，可为生态岛礁建设与维护提供重要的科学依据和技术支撑。