竖向平行双隧道开挖对邻近群桩变形的影响

The influence of excavation of vertically parallel twin tunnels on the deformation of nearby pile groups

为了研究砂土地层中竖向平行盾构隧道施工引起邻近群桩的变形与各影响参数间的一般性规律,基于离心模型试验,采用PLAXIS 3D建立竖向平行双圆隧道邻近既有群桩开挖三维数值模型。通过与离心模型试验实测结果对比,对数值模型进行验证,并研究了土体参数、隧道和桩基尺寸对群桩沉降和倾斜的影响规律。研究结果表明:隧道开挖引起的群桩沉降和群桩倾斜度随土体模量、地层损失率、隧道直径的增大而增大,随桩基长度的增大而减小;且当下部隧道位于群桩正下方时群桩沉降受土体模量、地层损失率、隧道直径、桩基长度的影响较大;当下部隧道位于群桩桩趾水平处时群桩倾斜受土体模量、地层损失率和桩基长度的影响最大;土体模量大于35 MPa后,群桩沉降不再增加;土体模量大于20 MPa后,群桩倾斜度变化明显放缓;当双隧道均位于群桩一侧时,桩基长度大于35 m后群桩沉降基本不再变化;第二隧道位于群桩正下方时,当桩基长度大于45 m后群桩沉降和倾斜度变化量明显减少。

In order to investigate the general principles governing the deformation of nearby pile groups induced by the construction of vertically parallel shield tunnels in sandy soil layers,this study utilizes centrifuge model tests and establishes a three-dimensional numerical model using PLAXIS3D for the excavation of vertically parallel twin circular tunnels adjacent to existing pile groups.By comparing the numerical model with the measured results from centrifuge model tests,the model's validity is confirmed,and the influence of soil parameters,tunnel dimensions,and pile foundation dimensions on pile settlement and tilt is investigated.The research findings indicate that the settlement and tilt of pile groups induced by tunnel excavation increase with the increase of soil modulus,ground loss rate,and tunnel diameter,while decreasing with the increase of pile length.Furthermore,when the lower tunnel is situated directly beneath the pile group,pile settlement is significantly influenced by soil modulus,ground loss rate,tunnel diameter,and pile length.When the lower tunnel is located at the level of the pile group toe,pile tilt is primarily affected by soil modulus,ground loss rate,and pile length.Pile settlement ceases to increase when the soil modulus exceeds 35 MPa,and pile tilt slows down noticeably when the soil modulus exceeds 20 MPa.Pile settlement remains relatively stable when both tunnels are located on one side of the pile group and the pile length exceeds 35 m.Moreover,when the second tunnel is positioned directly beneath the pile group,the change in pile settlement and tilt decreases significantly when the pile length exceeds 45 m.