基于荷载传递理论的山区嵌岩桩承载力分析

Analysis on Bearing Capacity of Socketed Pile in Mountainous Area Based on Load Transfer Theory

桩侧摩阻力是嵌岩桩承载力的重要组成部分,在提高嵌岩桩的竖向承载力中发挥着重要作用。为研究嵌岩桩的承载机理,以贵金古高速公路清池特大桥嵌岩桩承载力的现场监测为研究背景,分析了施工荷载作用下桩侧摩阻力的发展机理。基于嵌岩桩的桩-岩接触面的剪切特性,并经理论分析,推导了桩侧摩阻力与剪切位移的表达式。通过荷载传递理论,建立了嵌岩桩的荷载传递模型,利用Python实现四阶Runge-Kutta法求解该模型。工程桩的现场监测数据与计算结果吻合,表明了所建立的荷载传递模型的正确性以及计算方法的合理性,可用于研究嵌岩桩桩侧摩阻力的发挥机理。根据监测数据与荷载传递模型分析了不同施工荷载作用下剪切滑移阶段桩基截面轴力和剪切位移的特点。结果表明:施工荷载作用下,嵌岩桩的桩侧摩阻力由上到下逐渐发挥,承担了大部分施工荷载;当剪切位移达到极限剪切位移后,桩侧摩阻力逐渐保持稳定,施工荷载逐渐由桩端阻力承担;利用荷载传递模型计算的嵌岩桩截面轴力与和监测结果吻合,因此建立的荷载传递模型和计算方法具有实际的工程意义;计算的极限桩端阻力明显小于《公路桥涵地基与基础设计规范》(JTG 3363—2019)计算的极限桩端阻力,这说明原设计的极限桩端阻力偏安全,需要进行合理的修正。

Pile side friction is an important component of the bearing capacity of socketed piles,and plays a crucial role in improving the vertical bearing capacity of socketed piles.In order to study the load-bearing mechanism of socketed piles,on the study background of on-site monitoring of the bearing capacity of socketed piles of Qingchi Grand Bridge on Guiyang-Jinsha-Gulin Expressway,the development mechanism of pile side friction under construction loads is analyzed.Based on the shear characteristics of the pile-rock interface of socketed pile and theoretical analysis,the expressions of pile side friction and shear displacement are derived.A load transfer model of socketed pile is established based on the load transfer theory,and the model is solved by using the 4th-order Runge-Kutta method through Python.The on-site monitoring data of engineering piles are in accordance with the calculation result,indicating the correctness of the established load transfer model and the rationality of the calculation method,which can be used for study the mechanism of side friction of socketed piles.According to the monitoring data and the load transfer model,the characteristics of the axial force and shear displacement of the pile foundation section in the shear slip stage under different construction loads are analyzed.The result shows that(1)Under construction loads,the pile side friction of socketed pile plays a role from top to bottom gradually and bears most of the construction loads.(2)When the shear displacement reaches the ultimate shear displacement,the pile side friction remains stable gradually,and the construction loads are borne by the pile end resistance gradually.(3)The sectional axial force of socketed pile calculated by using the load transfer model is in accordance with the monitoring result,upon that the established load transfer model and calculation method have practical engineering significance.(4)The calculated ultimate pile end resistance is significantly smaller than that calculated according to the Design Specification for Highway Bridges and Culverts Foundations(JTG 3363—2019).This indicates that the original design of the ultimate pile end resistance is overly conservative and needs to be reasonably revised.