盾构双隧道不同开挖顺序及不同布置形式对管线的影响研究

在离心模型试验中同时考虑隧道开挖所致地层损失效应和质量损失效应,研究不同开挖顺序及不同布置形式下双隧道开挖对管线的影响规律。同时采用基于地层损失比的位移控制有限单元法对离心模型试验及其他4组拓展工况进行分析,其中土体本构模型采用考虑土体小应变特性的HP(Hypoplasticity model)模型,并将试验结果与已有的解析方法进行对比。研究结果表明,双隧道不同开挖顺序及不同布置形式对地表沉降、管线沉降、管线弯曲应变的影响显著;管线存在所产生的"遮拦"效应对管线正上方地表沉降的影响程度随着自由场最大地表沉降的增加而逐渐加剧;双隧道开挖所致管线沉降的主要影响区域为-1.2D_T~1.2D_T;实际工程中应加强浅埋后继隧道开挖时管线工作性状的监测工作,且不应简单采用叠加原理对不同施工工序及不同布置形式的双隧道开挖所致地表沉降、管线沉降及管线弯曲应变进行预测,应合理考虑后继隧道开挖所致土体的累计剪切应变及上覆隧道的遮拦效应对管–土相对刚度的影响。

Effects of twin shield tunneling with different construction sequences and different relative locations on adjacent pipelines

A series of three-dimensional centrifuge model tests are carried out to investigate the effects of twin shield tunneling with different construction sequences and different relative locations on an existing buried pipeline in dry sand. Both the volume loss effect and the weight loss effect are simulated by using an improved tunnel model. Meanwhile, a displacement controlled method based on ground loss and an advanced hypoplasticity constitutive model are applied for the three-dimensional numerical back-analyses of the centrifuge tests and the other four extended conditions. It is shown that the twin tunnels with different construction sequences and different relative locations greatly affect the surface settlements, pipeline settlements and pipeline bending strains. The influences of the shield effect induced by the existence of the pipeline on the ground surface settlement become more obvious with the increasing greenfield ground surface settlement. The major influence zone on the pipeline induced by tunneling is within ±1.2D_T. For practical engineering, it is necessary to enhance the monitoring of the serviceability of pipelines during the second tunneling with shallow depth. Remarkably, it should not simply adopt the superposition principle to predict the greenfield surface settlements, pipeline settlements and pipeline bending strains due to twin tunnelling with different construction sequences and different relative locations. The effects of the accumulated shear strain and the shield effect due to the existence of the upper tunnel on the relative pipe-soil stiffness should be reasonably considered.