深厚软土地基超载预压对桥梁桩基负摩阻力的影响

软土地基上的基桩，由于桩周土的向下运动，土与桩的摩擦增加了桩的下拉荷载，这就是桩侧的负摩阻力，负摩阻力的存在增大了桩基的变形甚至导致破坏。对此，以瓯飞堤穿越深厚软土区大桥群桩基础为工程实例，采用理论计算及三维有限元数值计算手段，分析工程实施过程中附加荷载施加对既有桩基工作环境影响。结果表明:由于负摩阻力的作用，桩身轴力随着深度的增加先增大后减小；桩侧摩阻力沿深度呈非线性变化；位移中性点位于黏土层与圆砾层交界处；群桩中各基桩空间分布不同，附加荷载引起同一承台下基桩-土变形协调存在差异，对桥桩安全监测应具有针对性。

Influence of Negative Friction Resistance to Bridge Piles under Surcharge Preloading of Deep Soft Soil Foundation

For the piles on soft soil foundation, due to downward movement of surrounding soil, the friction between soil and pile increases drag load on pile, i.e. negative friction resistance on pile side, leading to pile deformation, even damaged. Taking the pile group foundation of bridge with sea embankment across deep soft soil area as an engineering example, how the application of additional load affects the working environment of existing piles during construction, was analyzed by means of theoretical calculation and three-dimensional finite element numerical calculation. The results show that, due to the action of negative friction resistance, the axial force of pile first increases and then decreases with the increasing depth; and the friction resistance on pile side presents nonlinear variation along with the depth; the displacement of neutral point locates at the junction of clay and pebble layers; the spatial distribution of piles is different, and the pile-soil deformation compatibility under the same cap caused by additional load is different as well, thus the safety monitoring on bridge piles shall be targeted.