分层地基中富水隧道盾构施工对既有桥梁桩基的影响

Influence of water-rich tunnel by shield tunneling on existing bridge pile foundation in layered soils

当前盾构施工常需穿越大量桥桩基础,关于盾构开挖引起地下水渗流对邻近桥桩影响的研究较少。基于Winkler地基模型推导盾构施工对邻近桥桩变形的计算公式,建立整体和局部三维有限元模型。分析不考虑地下水作用、考虑稳定地下水作用及流固耦合三种计算工况下桥墩沉降量、地表沉降槽、桩身竖直、水平变形量及桩身应力变化趋势。研究结果表明:当不考虑地下水作用时,计算数值偏小;在流固耦合下开挖面的前上方土体渗流速度较周围土体的渗流速度快,在盾构通过后,两侧地下水在地表呈现出"U"形向隧道上方补给的流动趋势;桩身竖向变形以隧道顶部水平位置为界,上部桩身沉降,下部桩身向上变形;桩身水平变形呈现出连续"S"形分布,在隧道附近产生应力集中。流固耦合的计算结果与现场实测数据更吻合,符合实际情况。

At present,shield tunneling often needs to pass through a large number of bridge pile foundations.However,there are few studies on the influence of shield tunneling on adjacent pile foundations by combining with groundwater seepage.Based on Winkler model,the calculation equations of shield tunneling on vertical and horizontal displacement of adjacent bridge pile are derived.Meanwhile,full and part three-dimensional finite element models are established to analyze the trend of bridge pier settlement,ground surface settlement trough,vertical and horizontal displacement of the pile and pile stress under three calculation conditions,i.e.,not considering groundwater effect,considering stable groundwater effect and fluid-soil interaction.The results show that the calculated value is small when the effect of groundwater is not considered;the seepage velocity of the soil above the excavation face is faster than that of the surrounding soil under fluid-soil interaction,and after the shield passing,the groundwater on both sides shows a flow trend of“U”shape on the ground surface supplying to the upper part of the tunnel;the vertical displacement of the pile body is bounded by the horizontal position of the top of the tunnel,the upper pile body settles,and the lower pile body deforms upward.The horizontal displacement of pile body presents a continuous“S”shape distribution,causing stress concentration near the tunnel.The calculated results of fluid-soil interaction are in good agreement with the field measured data and accord with the actual situation.