循环荷载下钢管混凝土嵌岩桩钢-砼界面强度弱化机理及长期工作性状研究

Concrete-filled steel tube rock-socketed pile as a type of deep foundation is constantly used in deepwater wharf with shallow overburden and the construction of crossing-river bridges. The strength weakening of steel-concrete interface is the key to the reduction of bearing capacity and excessive accumulated deformation of the pile foundation under long-term cyclic loading. Nowadays, the lack of systematic theory and design methods leads the design of concrete-filled steel tube rock-socketed piles mainly refers to the specification of concrete filled steel tubular pile (column) or reinforced concrete rock-socketed pile, which can not conform to the actual bearing behavior, as a result, the normal service stage and even the security and stability of large wharf with such kind of foundation in China are threatened directly. On the mechanism, through mechanical properties experiments of steel-concrete interface, physical model tests of concrete-filled steel tube rock-socketed pile under cyclic loading and the basic mechanics analysis, this project reveals the strength weakening mechanism of steel-concrete interface, the force mechanism and deformation characteristics of concrete-filled steel tube rock-socketed piles. On the principle theory, integrating with materials science, geotechnical mechanics and structure calculation theory, the cyclic degradation model of steel-concrete interface, failure modes and calculation models of concrete-filled steel tube rock-socketed pile under cyclic loading are established in this project. On macro application, based on the aforementioned cyclic degradation model and calculation models, calculation methods of horizontal bearing capacity and accumulative horizontal deformation and deformation control methods of concrete-filled steel tube rock-socketed pile under cyclic loading are proposed to lay the foundation of application.

钢管混凝土嵌岩桩是在覆盖层较浅的深水码头及跨江桥梁建设中常采用的深基础型式。长期循环荷载下钢管混凝土嵌岩桩钢-砼界面强度弱化是导致桩基承载力弱化、累积变形过大的关键。目前，钢管混凝土嵌岩桩设计主要参照钢管混凝土桩（柱）或钢筋混凝土嵌岩桩规范，缺乏一套系统的理论和设计方法，与其实际承载特性不符, 直接影响我国采用此类基础的大型码头的正常使用甚至安全稳定。本项目在机理层面，通过循环荷载下钢-砼界面力学特性试验、钢管混凝土嵌岩桩物理模型试验和基本力学分析，揭示钢-砼界面强度弱化机理、钢管混凝土嵌岩桩受力机理及变形特性；在基本理论层面，结合材料科学、岩土力学及结构计算理论，建立钢-砼界面循环弱化模型、钢管混凝土嵌岩桩破坏模式及计算模型；在宏观应用层面，基于钢-砼界面循环弱化模型、钢管混凝土嵌岩桩计算模型，提出循环荷载下钢管混凝土嵌岩桩水平承载力及累积水平变形的计算方法和变形控制方法，奠定应用基础。

钢管混凝土嵌岩桩是在覆盖层较浅的深水码头及跨江桥梁建设中常采用的深基础型式。在船舶荷载、系缆力等水平循环荷载的长期作用下，钢管混凝土嵌岩桩钢-砼界面强度弱化是导致桩基承载力弱化、累积变形过大的关键。本项目主要针对循环荷载下钢-砼界面强度弱化机理、静载及水平循环荷载下钢管混凝土嵌岩桩承载性状、循环荷载下钢管混凝土嵌岩桩水平承载力计算方法等问题，采用模型试验、数值模拟及理论分析等手段开展研究，取得了以下创新成果：.1）开展了循环剪切荷载下钢-砼界面强度弱化试验研究，探明了钢-砼界面强度在粘结形态及脱粘形态下的弱化机理，确定了影响钢-砼界面粘结弱化的主要因素，阐明了钢-砼界面相对滑移规律和破坏过程，揭示了循环剪切荷载下钢-砼界面强度弱化机理，建立钢-砼界面在循环荷载作用下的强度弱化模型。.2）开展了静载下钢管混凝土嵌岩桩物理模型试验研究，阐明了静载下钢管混凝土嵌岩桩竖向、横向受力及受扭转条件下的承载性能，以及钢-砼界面在受力过程中的工作性状。.3）开展了循环荷载下钢管混凝土嵌岩桩水平承载性能模型试验，获得了不同循环荷载幅值、不同循环次数条件下钢筋混凝土桩身、钢管以及地基应力、变形的分布规律以及钢管混凝土嵌岩桩破坏模式。.4）结合钢-砼界面循环弱化模型及循环受载下钢管混凝土嵌岩桩破坏模式，提出了长期循环荷载下钢管混凝土嵌岩桩水平承载力计算方法。