基于渗流应力耦合的盾构隧道开挖对邻近桥梁桩基的影响

Influence of shield tunneling on pile foundation of adjacent bridge using fluid-soil coupling theory

基于Pasternak地基模型推导分层地基中盾构施工引起的邻近桩基竖向和水平位移理论解,并建立三维有限元模型,结合现场实测对比各种计算工况下桥墩沉降量和桩身竖向位移。同时,基于流固耦合理论分析桩身的竖向、水平向和沿隧道纵向的位移过程及桩身应力变化趋势。研究结果表明:流固耦合下开挖掌子面上方土体渗流速度较周围土体的渗流速度快,盾构通过后隧道两侧地下水表呈现出“U”形向隧道上方补给的流动状态;桩身竖向位移以隧道顶部水平位置为界,上部桩身沉降,下部桩身向上位移;桩身水平位移呈现出“S”形分布,在隧道附近产生应力集中;桩身竖直和水平向位移在盾构通过桩基后10环(15 m)趋于稳定,桩身沿隧道纵向位移最大值出现在盾构到达桩基位置处,之后出现部分回弹;考虑流固耦合分析的桥墩沉降计算结果与现场实测结果相吻合。

Based on Pasternak model,the analytical solution of vertical and horizontal displacements of adjacent pile foundation caused by shield tunneling was derived.Meanwhile,a three-dimensional finite element model was established to compare the settlement of bridge pier and vertical displacement of pile body under various calculation conditions in combination with field measured data.Based on the theory of fluid-soil coupling,the displacement process of pile vertical,horizontal and along the tunnel as well as the change trend of pile stress were analyzed.The results show that the seepage velocity of the soil above the shield machine is faster than that of the surrounding soil during the fluid-soil coupling,and after the shield passes,the ground water on both sides shows a flow state of"U"shape supplying to the upper part of the tunnel.The vertical displacement of pile is bounded by the horizontal position at the top of the tunnel.The upper pile body settles and the lower pile body deforms upward.The horizontal displacement of pile body presents an S-shaped distribution,causing stress concentration near the tunnel.The vertical and horizontal displacement of the pile tends to be stable after the shield passes through the pile foundation 10 rings(15 m).The maximum value of the longitudinal displacement of the pile along the tunnel appears at the position where the shield reaches the pile foundation,and then partial rebound appears.The pier settlement calculated results of fluid-soil coupling analysis are in good agreement with the field measured results.