倾斜岩层面的软岩嵌岩群桩承载机理研究

Large diameter rock-socketed piles are generally adopted in bridge and aqueduct foundations, where the bedrock is weak and the bedrock surface is inclined. Rock-socketed pile group with inclined rock surface would appear some limitations such as slip along the rock surface, buckling by squeeze and expansion of piles, and uneven settlement. Due to the factors including weak properties of bearing layer, inclined rock surface, unequal lengths of piles, specialty of pile - rock interface, and complicated load condition, this kind of foundation should be investigated systematically and deeply in order to resolve these limitations. In this project, the CT scan technology will be used to realize visualization and quantification of deformation form and development of the model test of rock-socketed piles, as well as reveal the embedded mechanism in micro aspect. Meanwhile, the expansion theory will be used to investigate the bearing mechanism of rock-socketed pile in soft rock and its stress path in order to give the computational formula of ultimate bearing capacity. Moreover, we will conduct triaxial test with stress path, dynamic triaxial test and pile-rock contact test, and propose the static and dynamic constitutive model of soft rock as well as the pile-rock interface model. Finally, considering the nonlinear interaction of structure - pile group - soil, the centrifugal modeling test and shaking table test will be carried out to investigate the bearing mechanism, failure mode, dynamic characteristic and seismic response of rock-socketed piles in soft rock with inclined bedrock surface. Based on the results of model tests, theoretical analysis, and numerical simulation, this project will propose the calculating methods, design criteria considering both bearing capacity and settlement, reinforcement measures, and vibration-absorption measures, which would be applied in actual engineering projects.

桥梁、渡槽基础往往采用大直径嵌岩桩，其基岩软弱且岩面倾斜。倾斜岩面软岩嵌岩群桩存在沿岩面滑移、群桩挤扩压屈、不均匀沉降等问题；由于持力层性质差、岩面倾斜、基桩非等长、桩-岩界面特殊、荷载条件复杂等因素，该群桩的承载机理需进行系统深入的研究。本项目引入CT扫描技术进行嵌岩桩模型试验，实现变形及发展的可视化，从细观角度揭示嵌固机理；采用扩孔理论研究软岩嵌岩桩的承载机理和应力路径，建立其极限承载力的计算公式；进行软岩应力路径三轴、动力三轴和桩-岩接触特性等试验，建立软岩的静动力本构模型、桩-岩界面本构模型；进行群桩离心模型试验和振动台模型试验，考虑承台-群桩-岩土体非线性共同作用，研究倾斜岩层面的软岩嵌岩群桩的承载机理与破坏模式、动力特性与地震响应。综合模型试验、理论分析和数值模拟结果，提出倾斜岩层面的软岩嵌岩群桩的设计计算方法、承载力与沉降双控设计准则、加固与减震措施，并在实际工程中推广应用。

嵌岩桩广泛应用于高层建筑、大跨度桥梁以及海洋石油钻井平台等工程中，具有承载力高、沉降小和抗震性能好等优点。软岩在世界范围内分布普遍，工程中也大量采用了软岩嵌岩桩基础，并且其中很多基础持力岩层的顶面是倾斜的。本项目通过单元试验、室内模型试验、CT扫描可视化、振动台试验、理论分析和数值模拟等手段，开展了软岩力学特性、桩端承载机理、桩侧界面特性、单桩竖向承载特性、群桩承载特性和沉降计算、群桩地震响应等方面的研究。研究结果表明，桩基承载力随着嵌岩桩径、嵌岩深度、上覆压力的增大而增大；随着桩顶荷载增大，桩侧摩阻力自上而下逐步发挥，桩端荷载分担比例逐渐增大，桩身侧摩阻力近似呈R型分布；桩身平均侧摩阻力随着桩顶位移的增加而增大，基本呈双曲线关系。根据桩-岩界面试验，提出了考虑桩-岩界面咬合、磨损作用的界面本构模型。CT扫描试验从细观角度揭示了桩端软岩的破坏模式为球孔扩张模式，桩端下软岩压密区范围为桩端深度方向1.2d～1.3d。采用球孔扩张理论研究软岩嵌岩桩的承载机理，提出了极限承载力的计算公式。开展了群桩模型试验和振动台模型试验，综合模型试验、理论分析和数值模拟，提出了倾斜岩层面的软岩嵌岩群桩的沉降计算方法、承载力与沉降双控设计准则、加固和减震措施。该项目的研究成果具有较大的理论价值和实用价值。