桩底盾构施工引起的桩基承载力损失计算

提出一种桩底盾构施工引起的桩基承载能力损失计算方法.先实现考虑卸载过程的双曲线荷载传递函数编译,然后利用该桩土接触模型得到隧道开挖前和开挖后的Q～s曲线;取s=50mm时对应的荷载为桩基极限承载能力,采用桩基极限承载力损失百分比作为隧道开挖对桩基承载性能影响的评价指标.结合杭州地铁1号线某工点实例,分析了桩基承载曲线变化特征、桩体内力变化规律和承载力损失影响因素.案例中,盾构施工体积损失率控制在0.5%时,桩基承载力损失值为22%.隧道开挖后,桩体中存在一点侧摩阻力不变,在该点上部桩体侧摩阻力增大,在该点下部桩体侧摩阻力有所减小.承载力损失值随着体积损失率的增大而增大;桩基的初始荷载水平越大,承载力损失值越大;桩底与隧道顶部的距离越大,桩基承载力损失值越小.

Calculating Method of Pile Bearing Capacity Loss Induced by the Tunnel Excavation Underneath the Pile

A method was proposed to calculate the pile bearing capacity loss induced by the tunnel excavation underneath the pile. The hyperbolic load transfer function considering the effect of tunnel excavation at the pile soil interface was compiled and based on it, the Q~s curves of the pile and that after tunnel excavation were figured out. Ultimate bearing capacity of pile was confirmed where pile settlement was fifty millimeter, and it was used as the indicator to measure the influence caused by the excavation. The variation of bearing curve and pile forces as well as influencing factors to the bearing capacity were analyzed based on one work point of Hangzhou Metro Line 1. The bearing capacity loss of pile is 22% when volume loss rate is controlled at 0.5%. After tunnel excavation, there is a position in the pile where the lateral friction is unchanged, while the lateral friction increases upper the position and decreases bellow the position. The bearing capacity loss has a positive correlation with volume loss rate and Initial load of pile, however, has a negative correlation with the distance between the bottom of the pile and the top of the tunnel.