基于分形理论的人工挖孔嵌岩桩承载特性分析

嵌岩长桩的承载性能主要取决于桩-岩接触面的剪切强度。基于岩体结构面强度的研究方法，引入分形维数描述的两相接触介质粗糙表面的抗剪强度公式，建立了以分维数表示的嵌岩桩侧摩阻力传递模型，求得了弹性条件下的桩侧摩阻力及桩身轴力的解析式。基于所获得的解答，深入地探讨了分形维数D对桩侧摩阻力?、桩身轴力P及桩端荷载分担比Pb/Pd的影响规律。研究表明:同等条件下一定范围内粗糙分维值D越大，桩侧摩阻力在桩身上部分布越集中，荷载传递深度越小，桩端荷载分担比Pb/Pd也越小；长径比l/d越小，桩端荷载分担比越大，反之越小。工程算例对比分析表明:理论计算与实测结果吻合较好，对嵌岩桩设计有一定参考价值。

ANALYSIS OF BEARING CAPACITY CHARACTERISTIC OF ROCK SOCKETED PILES BASED ON FRACTAL THEORY

The bearing capacity of rock-socketed long-piles depends on the shear strength of pile-rock contact surface. Based on the research method of rock mass structural surface intensity and introducing the shear strength formula of two-phase contact medium rough surface described by fractal dimension, the shaft resistance transfer model of a rock-socketed pile expressed by fractal dimension is set up. Then the analytical solutions of the pile shaft resistance and pile axial force under the elastic condition are obtained. Based on the solution obtained, the influence law that how the fractal dimension influence the shaft resistance, pile axial force and the load distribution ratio of pile tip were discussed. The research show that in a certain range and under the same conditions, the higher the fractal dimension of rough D is, the higher the concentration extent of shaft resistance in the upper part of a pile is，the smaller the depth of a load transfer and the load distribution ratio of pile tip are. The smaller the length-diameter ratio l/d is, the bigger the load distribution ratio of pile tip is. Comparative analysis result of an engineering example shows that the calculated values by the present method agree well with the measured data.