桩基施工及承载阶段对运营盾构隧道的影响

Influence of Construction and Loading Stage of Overpass Pile Foundation on Existing Running Shield Tunnels

针对合肥某立交桥上跨既有盾构隧道工程,通过有限元数值模拟方法对单桩邻近隧道施工进行参数敏感性分析,并进一步研究立交桥单桥墩桩基础与双桥墩桩基础在施工及承载阶段对盾构隧道管片变形与内力的影响;通过对比分析2种立交桥跨越既有盾构隧道方式下的地表沉降、盾构隧道管片及铁轨变形,探讨2种跨越方式在工程应用中的优劣。研究结果表明:1)单桩对邻近隧道结构的影响,随着桩长、桩径的增加而增大;随着桩隧净间距的增大而近似呈指数函数形式降低。2)当桩长与隧道埋深比值大于1时,增加桩长是减小隧道结构变形的有效途径。3)单桥墩桩基础施工阶段对盾构隧道的影响效应小于承载阶段,管片位移以沉降为主。承载阶段随着荷载的增加,横向轴力与弯矩在靠桩一侧拱腰位置变化最大,纵向轴力与弯矩在拱顶位置变化最大。4)双桥墩桩基施工及承受上部荷载时,较单桥墩而言同一管片处的沉降增大0.3mm,水平向位移减小0.56mm。经比较,中间无桩的跨越隧道方式更优。

In view of the construction condition that an overpass crosses over existing shield tunnels in Hefei,the construction parameter sensitivity analysis of single-pile adjacent to tunnel is carried out by finite element numerical simulation method,and the influence of single-bridge pile foundation and double-bridge pile foundation of overpass on the deformation and internal force of shield tunnel segment during construction and load-bearing stage is further studied. By comparing and analyzing the ground settlements,shield tunnel segments and track deformations under two crossingover modes of the overpass,the advantages and disadvantages of the two modes in engineering applications are discussed.The results show that:(1) The influence of single-pile on the adjacent tunnel structure increases with the increase of pile length and pile diameter;and decreases with the exponential function as the net spacing of piles and tunnels increases.(2) When the ratio between pile length and tunnel burial depth is greater than 1,increasing the pile length is an effective way to reduce the deformation of the tunnel structure.(3) The effect of the single-pier pile foundation construction on the shield tunnel is less than that of the loading stage,and the displacement of the segment is dominated by settlement;with an increase in the loading steps,the lateral axial force and transverse bending moment vary most in the tunnel arch which on the side of pile foundation;the longitudinal axial force and longitudinal bending moment vary most in the position of the tunnel vault.(4) When constructing double bridge pile foundation bearing upper load,the settlement at the same segment increases by 0.6 mm and the horizontal displacement decreases by 0.56 mm compared to the single-pier pile foundation.The method of crossing the tunnel without the intermediate pile is better.