吸力桶与圆沉箱整体预制式新型离岸深水码头的稳定性研究

Combining the advantages of suction bucket foundations and circular caissons, this project proposes a new type of entirely prefabricated offshore deep-water wharf composed by suction bucket foundations and circular caissons, which is suitable for soft foundation and has a high bearing capacity, great stiffness, good durability, cost saving and small effect on the environment. While berths can be placed on the shoreward side of the wharf, the wharf itself can act as a breakwater on the other side. The new offshore deep-water suction wharf is suitable for rough wave conditions and has a wide application prospect. The problems of simulating the large deformation of soil during the penetration of skirts, quantitatively calculating the dynamic damage of soft soil from the penetration process and cyclic loading of strong storms afterwards, and evaluating the capacity of this new structure under combined loading of wave force, ship mooring force, gantry crane loading etc. are key problems in studying the stability of this new structure on soft foundation. In view of these problems, a dynamic damage constitutive model of soft soil, which takes strain softening and rate effects into account, will be established. A study of soil flowing mechanism during the penetration of skirts using the damage model of soil-structure interface combined with large deformation numerical methods and model tests will be carried out, to summarize the foundation damage from the penetration of skirts and applied loads. Furthermore, a method to evaluate failure envelopes of this new wharf structure will be proposed, and the evolution of the failure envelopes after penetration and applied loads will be studied subsequently, as well as its bearing mechanism. The research results can provide the theory base for the engineering application of the new structure.

结合吸力桶和圆沉箱的优点，本项目拟提出吸力桶与圆沉箱整体预制式新型离岸深水码头，该结构适用于软土地基，具有承载性能好、结构刚度大、耐久性好、费用省和对环境影响小的优点，其靠岸侧可布置泊位，靠海侧可兼做防波堤，抗浪能力强，应用前景广泛。如何模拟桶壁贯入时土体的大变形，如何定量计算桶壁贯入和强风浪的持续循环作用对软土的动态损伤，如何评价这种新型结构在波浪力、船舶系缆力和门机荷载等作用下的复合承载力是研究软基上这种新型结构稳定性的关键问题。本项目拟建立可考虑软土应变软化和率效应的软土动态损伤本构模型；并结合大变形数值方法、模型试验和接触面损伤模型，研究桶壁贯入时土体的流动机制，总结桶壁贯入和外荷载对地基的损伤规律；结合承载力破坏包络面理论，建立这种结构复合承载力的评价方法，研究其破坏包络面在桶壁贯入后、外荷载作用下的演化规律，并探究其承载机理，研究成果可为这种新型结构的工程应用提供理论基础。

为了开发适应软土地基和恶劣波浪条件的离岸深水码头，提出了吸力桶与圆沉箱整体预制式新型离岸深水码头，阐述了其结构组成、平面布置和施工工艺，分析了其承载特性。在边界面模型的基本理论框架之上，开发了可考虑初始各向异性的边界面本构模型，利用Mises三维化方法和隐式积分方法将其二次开发至ABAQUS有限元软件中,在边界面中加入与应变速率相关的应变率函数，设置软化函数对硬化准则进行修正，将塑性累积应变作为软化函数的主要变量，并在软化函数中设置残余强度，使得土体在结构性完全丧失或者循环荷载软化作用后仍然具有一定的强度残余。在结构性软土中设置结构面，考虑土体的结构性导致土体强度的提高。建立了考虑应变软化对土体强度影响的三维大变形有限元分析模型，并与离心机实验进行了验证，研究了桶内雍高、土体流动机制的演变和强度软化的分布规律，提出了可以预测部分重塑条件下桶形基础在软土地基中贯入阻力的理论公式。基础的安装过程会引起桶内土体的隆起和土体强度的重塑。基础的承载力在安装后因受到这两种效应的影响而显著降低。所有水平和力矩组合承载力包络线的最大降低值始终大于垂直、水平或力矩单向承载力的降低值。当竖向荷载小于竖向承载力的一半时，安装效应对基础安装后承载力的影响更为明显。在贯入比较浅时，吸力桶与圆沉箱整体预制式新型离岸深水码头的基础内部或外部隔室内土体表面的平均高度明显高于空心桶形基础。然而，当采用内桶直径为外桶直径的一半时，随着贯入深度的增加，外隔仓中较大的摩擦阻力阻碍土壤向上流动，而内隔仓中的摩擦阻力推动大量土壤向下移动。当贯入深度相对较大时，内、外隔仓之间的土壤高度差异过大将对基础承载力产生不利影响。通过扩大内桶直径与桶基础外径的比值，可以有效地改变土体流动规律。研究得出最佳内桶直径为外径的5/8，在这种情况下，内、外隔仓土体表面高度几乎相等。通过在基础裙底设置外开角，可以有效降低桶内土塞高度。为了研究外开角对桶内土塞、土体软化和贯入阻力的影响，在考虑土体变形和应变软化等的情况下，建立了有不同外开角的基础贯入阻力分析模型。研究发现，随着角度的增加，更多的土体被引导并流出桶外，桶内土体表面的高度明显降低。建议将60°作为基础端部外开角的最佳角度，以尽量减少桶内土塞。研究了结构贯入后又遭遇波浪力等荷载时的结构稳定性、复合承载特性和承载机理。研究成果对软基上近海结构物的稳定性研究具有普遍借鉴意义。