盾构隧道近距离侧穿立交桥桩基的变形影响分析

Deformation Effect Analysis of Shield Tunnel Closely Side-passing Viaduct Pile Foundation

[目的]盾构掘进会引起附近桥梁基础发生位移变形,降低桥梁基础承载能力,为此结合某工程实例对盾构隧道近距离侧穿桥梁桩基的变形影响进行研究。[方法]依托合肥地铁5号线盾构侧穿立交桥桩基工程,建立三维数值模型,分析盾构施工引起的桩基横向水平位移、纵向水平位移以及桩基沉降规律。[结果及结论]研究结果表明,桩底横向水平位移呈现“离开—靠近—离开”隧道的动态变化,桩身横向水平位移近似“C”形扰曲曲线,位移沿桩深呈先增大后减小的变化趋势,极值位于桩深9~10 m处。桩底纵向(平行隧道轴向)水平位移表现为“双峰”形曲线,盾构通过桩基后,桩身发生与掘进方向相反的纵向位移,在盾构通过桩基12 m后桩身纵向水平位移出现回弹变化,表明盾构掘进对桩基的纵向变形影响一定程度上是可逆的。桩基沉降变化呈陡峭趋势,同侧桩基距离隧道越近沉降越大,且远侧隧道开挖会引起桩端二次沉降,最大沉降值发生在4号桩基桩底处,沉降值为4.94 mm。

[Objective]Shield tunneling may cause displacement and deformation of the nearby viaduct foundation and reduce its bearing capacity.Therefore,the deformation effect caused by shield tunnel closely side-passing viaduct foundation is studied based on an actual project.[Method]Relying on the project of Hefei Metro Line 5 in which the shield tunnel passes the pile foundation of the viaduct on the side,a three-dimensional numerical model is established to analyze the horizontal displacement,the longitudinal displacement and the settlement pattern of the pile foundation caused by shield construction.[Result&Conclusion]The research results show that the horizontal displacement at the pile bottom presents dynamic changes of leaving,approaching and leaving the tunnel.The horizontal displacement of the pile body is similar to a C shape flexture curve.The displacement increases first and then decreases along with the pile depths,and the extreme value is located at the pile depth of 9~10 m.The longitudinal displacement at the pile bottom(parallel to the tunnel axis)shows a bimodal curve.After the shield passing the pile foundation,the pile body undergoes longitudinal deformation in the opposite direction of the excavation.After the shield passing through the pile foundation for 12m and further,the horizontal displacement of the pile body in longitudinal direction rebounds,indicating that the influence of shield tunneling on the longitudinal deformation of the pile foundation is reversible to a certain extent.The settlement of the pile foundation presents a steep trend.The closer the pile foundation at the same side is to the tunnel,the greater the settlement.Moreover,the excavation of the far side tunnel will cause secondary settlement of the pile top.The maximum settlement occurs at the bottom of the No.4 pile foundation,and the settlement value is 4.94 mm.