隧道下穿码头群桩基础的离心模型试验研究

Centrifugal Model Test Research on Pile Group Foundation of Tunnel Under Wharf

在地下隧道施工中遇到既有桩的情况并不少见,尽管近年来隧道--土--桩相互作用引起了广泛关注,但以往的研究主要集中在小规模隧道开挖引起的桩的反应上。通过三维离心模型试验,研究了双管大型隧道开挖引起的群桩变形机理。由于隧道开挖引起的应力释放,群桩的实测沉降随隧道的推进几乎呈线性增加。监测点距新建隧道较短,导致群桩沉降较大。单隧道开挖完成后,在隧道中心线正上方观测到最大桩群沉降为0.23%D(即隧道直径)。双管开挖后,最大群桩沉降增加到0.32%D,最大群桩沉降位置向两隧道之间的中心线移动。随着开挖面接近监测断面,既有桩群迅速向开挖面倾斜。当隧道工作面通过监测断面时,减少了现有群桩的倾斜。显然,当隧道工作面位于监测断面正下方时,测得的群桩倾斜达到最大值。这清楚地说明了隧道开挖引起群桩的三维变形机理。若将隧道开挖简化为二维问题,则忽略了群桩沿隧道纵向的倾斜,而群桩的倾斜位于非保守侧。

It is common to encounter existing piles during tunnel constructions in congested underground.Although tunnel-soil-pile interaction has attracted much research attention recently,previous studies mainly focused on pile responses due to small-scale tunnel excavation.In this study,three-dimensional centrifuge test is conducted to investigate deformation mechanisms of a pile group due to twin large-scale tunnel excavations.Due to tunneling-induced stress relief,the measured settlement of pile group increases almost linearly with tunneling.A shorter distance between the monitoring point and new tunnel results in larger pile group settlement.Upon completion of a single tunnel excavation,a maximum pile group settlement of 0.23%D(i.e.,tunnel diameter)is observed directly above tunnel centerline.After twin tunnel excavations,the maximum pile group settlement is increased to 0.32%D,and the location of the maximum pile group settlement shifts to the centreline between two tunnels.As tunnel face approaches the monitoring section,the existing pile group tilts rapidly toward tunnel face.As tunnel face passes through the monitoring section,tilting of existing pile group is reduced.Obviously,the measured tilting of pile group reaches a maximum value when tunnel face is located directly beneath the monitoring section.This clearly demonstrates three-dimensional deformation mechanisms of pile group due to tunnel excavation.If tunnel excavation is simplified as a two-dimensional problem,tilting of pile group along longitudinal tunnel direction is ignored,which is on unconservative side.