考虑沉贯过程的吸力式沉箱基础抗拔破坏机理研究

Suction caissons is widely used as the offshore platform foundation due to its easy construction, reuse and low cost. Offshore platform is often subjected to wind, wave and other cyclic loading besides the self-weight; meanwhile the penetration of the suction caisson would also have effect on the platform stability. So it is necessary to take the influences of penetration process and long-term cyclic loading on the bearing behavior into consideration. This project is intended to explore the penetration effect on the suction caisson bearing behavior and obtain the failure modes under static and cyclic loading based on model tests. Then, a reasonable contact model and bearing capacity analysis model of suction caissons are established as well as the failure mechanism. Finally, based on the above research, the calculation method of ultimate bearing capacity of suction caisson would be suggested. The results of the research can help us to further understand failure mechanism of suction caisson, and obtain the improved calculation method of suction caisson, which can provide a scientific basis for the suction caisson design in practice.

吸力式沉箱基础因具有施工简单、可重复利用及造价低等优点，在海洋平台建造中得到了广泛的运用。海洋平台在正常工作中，不仅受到上部平台的自重外还经常受到风、浪等长期循环荷载作用，同时吸力式沉箱基础的安装过程也会对海洋平台的稳定性产生影响，所以在吸力式沉箱基础的设计过程中有必要考虑贯入过程及长期循环荷载对其承载特性的影响。本项目通过模型试验和理论分析相结合的方法研究吸力式沉箱基础的贯入过程对其承载特性的影响以及静荷载、长期动力循环荷载作用下吸力式沉箱基础的破坏性状，建立吸力式沉箱基础与土的接触弱化模型，提出吸力式沉箱基础的破坏模式并建立对应的承载力分析模型，最后揭示吸力式沉箱基础的破坏机制并提出对应的极限承载力计算方法。研究成果在进一步明确吸力式沉箱基础的破坏机理的同时，完善了吸力式沉箱基础的承载力计算方法，为吸力式沉箱基础海洋平台的设计提供一定的科学依据。

吸力式沉箱基础是一种新型海洋平台基础结构型式，它具有施工简便、可重复使用及造价低等优点，在海洋工程中应用具有广阔前景。本项目通过室内试验、理论分析和数值模拟相结合的方法研究了吸力式沉箱基础在长期静载下的承载性状及循环荷载作用下土体的软化效应对抗剪强度的影响。利用动三轴仪开展试验，研究了黏粒含量、干密度、固结围压、动应力比和振动频率的影响；利用动、静三轴仪，对比研究了试样静荷载作用下的抗剪强度与循环荷载作用后试样的静抗剪强度，得到了不同围压、超固结比下的地基土的抗剪强度及破坏孔压比的变化规律；自行研制了吸力式沉箱基础抗拔承载力试验系统，得到了吸力式沉箱基础在受到不同荷载作用点倾斜荷载作用时的包络线图；建立了沉箱基础分别受到竖向荷载、水平荷载以及水平-弯矩复合荷载的作用下沉箱及土颗粒模型，进一步明确了沉箱基础在不同加载模式下的破坏机理。研究成果可进一步明确循环荷载作用下土体的软化效应对土体抗剪强度的影响，揭示吸力式沉箱基础的承载机理、完善吸力式沉箱基础的极限承载力计算方法，为吸力式沉箱基础海洋平台的设计和应用推广提供理论依据。