含气粘土循环弱化宏细观机制及其对海洋桩基循环特性影响

Discrete gas bubbles are widely formed in the shallow clayed seabed within 200 km offshore, China. The cyclic degradation of the gassy clay governs the performance of the foundations in the gassy seabed. Due to the complex interaction between the gas bubbles and the soil skeleton, a slight change in gas content would have either worsen or suppress cyclic degradation of gassy clay at a given effective confining stress. This uncertained cyclic responses have imposed additional risk on the cyclically loaded foundations in the gassy seabed. This proposed research is directed towards the fundamental scientific issue on the macro-meco interaction mechanism between the bubble and the soil skeleton. Firstly, cyclic triaxial tests will be performed in a CT scanner. On the macro level, the detrimental or beneficial effects of different contents of gas on the cyclic degradation of gassy clay will be studied. While on the meco level, the interaction mechanism between the bubble and the soil skeleton will be revealed. Based on the newly understood macro-meco cyclic degradation mechanism of gassy clay, a cyclic stiffness degradation model will be developed and implemented into a finite element program. Secondly, numerical analysis and centrifuge model tests will be carried out to investigate the role played by different contents of gas in worsening or suppressing the cyclic degradation of reaction forces acting on the pile, and the cumulative lateral pile displacement. The correlation between the degradation and accumulation factors and the initial compression wave velocity (which characterises the initial gas content) of the gassy seabed will be established. Lastly, an analysis method for cyclic soil-pile interaction considering compression wave velocity will be proposed, in order to furnish scientific support for tackling the difficulty in designing piled foundations in gassy clayey seabed.

我国离岸200公里内广泛分布含有游离状微气泡的粘土海床，含气粘土的循环弱化特性对基础承载性状有重要影响。气泡和粘土骨架间的复杂相互作用，导致同一有效应力下，气泡的微量变化就可能显著加剧、也可能抑制土骨架刚度的循环弱化程度，这给含气海床中循环受荷桩基带来安全隐患。本项目围绕“气泡-土骨架”相互作用宏细观机制这一关键科学问题，首先，开展CT扫描环境中含气粘土循环加载试验，宏观上揭示不同含气量对土骨架循环弱化的加剧或抑制效应，细观上探明诱发上述效应的“气泡-土骨架”作用内在机制，据此建立含气粘土循环刚度弱化模型，开发相应数值计算方法。其次，结合数值模拟和离心模型试验，阐明粘土海床中不同含气量对桩周土反力循环弱化、水平位移累积的加剧或抑制效应，并量化上述效应与海床初始压缩波速（表征含气量）的关联。最后，提出基于海床初始压缩波速的桩-土循环相互作用分析方法，为解决粘土海床上的桩基设计难题提供依据。

滨海软土中常赋存圈闭大气泡。针对滨海含气软土海床中桩基循环受荷变形控制难题，围绕圈闭气相-土骨架耦合作用科学问题，取得创新：首次建立了能统一描述圈闭气相劣化/强化土骨架力学性能的滨海含气土本构模型；提出了含气海床中桩-土循环p-y模型和刚度弱化分析方法；构建了含气地基变形定量评价方法，发现了地基中气压与有效应力比值超临界值是诱发气相劣化效应和地基变形过量的根源，据此提出了调控气压与有效应力比的含气地基变形控制技术，实现了滨海含气地基上多项重大工程的微沉降控制。.项目资助期间发表期刊论文47篇（其中24篇标注，SCI论文20篇），ESI高被引1篇。任TUST等国际期刊特刊主编，获省部级奖1项。获国际土力学及岩土工程学会杰出岩土工程青年奖，是迄今唯一获奖华人。