大直径盾构隧道下穿既有高速公路桥涵影响分析

Analysis of the Impact of Large Diameter Shield Tunnel Crossing Existing Expressway Bridge and Culvert

为进一步研究大直径盾构隧道掘进时对周边建(构)筑物的影响,依托成都某铁路工程大直径盾构隧道小间距、浅覆土下穿高速公路桥涵工程,采用数值模拟分析方法,考虑桩-土-隧道相互作用,建立三维有限元计算模型,分析盾构隧道施工引起地表、桥桩、人行地道及隔离桩位移变化趋势。结果表明:盾构隧道开挖卸荷在地表形成了明显的沉降槽,但隔离桩能有效阻断土体变形,减小地表沉降;地表横向沉降曲线在隔离桩位置出现突变,隔离桩前及背后的地表沉降量降幅分别达27%及40%~50%;地表纵向沉降曲线在隔离桩范围数值减小且呈W形分布。桥桩受盾构隧道开挖卸荷影响,产生向隧道侧的附加变形及弯矩,洞身范围其变形值从下至上先增大后减小,且较小直径盾构隧道对桥桩竖向影响范围大;同时盾构隧道下穿人行地道引起结构底板附加变形较大,沉降最大值达7.5 mm;上述相关数值计算结果与现场实测结果较为吻合,验证了数值模拟结果的准确性。

To further investigate the influence of large diameter shield tunnel construction on the surrounding struc⁃tures,based on a large diameter shield tunnel project of a railway engineering in Chengdu,combined with the char⁃acteristics of small spacing and shallow soil crossing highway bridge and culvert,the numerical analysis method is adopted to consider the interaction between pile-soil-tunnel,and a three-dimensional finite element calculation model is established.The displacement trends of ground surface,bridge pile,pedestrian tunnel and isolation pile caused by shield tunnel construction are analyzed,The simulation results show that the excavation unloading of shield tunnel forms an obvious settlement trough on the surface,but the isolation pile can effectively block the soil deformation and reduce the surface settlement;the horizontal surface settlement curve shows a sudden change at the position of the isolation pile,and the surface settlement value before and behind the isolation pile decreases by 27%and 40-50%respectively;the vertical surface settlement curve decreases in the range of the isolation pile and shows a W-shaped distribution.The bridge pile is affected by the tunnel excavation unloading,and produces additional de⁃formation and bending moment to the tunnel side.The value of the tunnel body range increases from the bottom to the top and then decreases,and the vertical influence range of the small diameter shield is tunnel large.At the same time,the additional deformation of the structure floor caused by the shield tunnel under the pedestrian tunnel is large,and the maximum value of settlement is 7.5 mm.The above numerical calculation results are close to the field measured results,which verifies the accuracy and feasibility of the numerical simulation results.