软硬不均地层中盾构施工引起的地层隆沉预测

Ground vertical displacements due to shield tunnelling in double-layer soil

将刚度当层法与Mindlin基本解相结合提出双层弹性体系下盾构施工引起地层隆沉的计算方法,该计算方法可以同时考虑开挖面处不平衡力、盾壳–土体间摩擦力、盾尾同步注浆压力、二次补偿注浆压力、施工期间地层附加荷载及地层损失6个施工因素对地层隆沉的贡献,同时可以反映上下地层刚度差异对地层隆沉的影响。研究发现,当盾构浅埋时,其在上下刚度不均地层中掘进引起的地表隆沉与其在单一软或单一硬地层中掘进引起的隆沉差别较大;当盾构埋深逐渐增大时,这个值逐渐接近盾构在单一软地层及单一硬地层中掘进引起隆沉的平均值,此外研究发现,二次注浆范围从全断面至未注浆变化时,地层的隆起值先增大后减小最后变为0,当注浆范围为上半断面时,注浆补偿效果最好。从京张高铁清华园隧道的实测数据与理论计算对比分析可以发现:提出的双地层模型可以较好地反映开挖面前方地表的隆起及开挖面后方先沉降后隆起再稳定的规律,且比基于单一地层模型采用加权平均法计算得到的隆沉值更接近实测值,计算误差可减小11.08%。研究成果可为盾构在单一地层及软硬不均双层地层中施工引起的地层隆沉的预测提供理论指导。

A method for calculating ground vertical displacements of double-layor elastic system due to shield tunneling was proposed combining the stiffness equivalent method with the Mindlin solution,which can simultaneously consider the unbalanced force at the tunnel face,the friction between the shield skin and the soil,the grouting pressure of the shield tail,the secondary grouting pressure,the additional load during tunnelling and the volume loss,and can also reflect the influence of the stiff difference of adjacent layers on ground displacements. The results show that the calculated ground vertical displacement induced by tunnelling in double-layer soil is different from that in single-layer soil while the overburden thickness is shallower,and close to the average value of the ground displacements calculated in soft and hard layers when the overburden thickness is getting deeper. It is also shown that the ground heave value first increases,then decreases and finally goes to zero with the secondary grouting ranging from the full face to the ungrouted zone and that the optimal grouting range is within the upper half. Comparisons between the ground vertical displacements of the field measurement and the theoretical calculation of Qinghuayuan Tunnel of the Jing-Zhang High Speed Railway indicate that the proposed double-layer model can describe the pattern of soil heave ahead of the tunnel face and settle-heave-stabilization behind of the tunnel face and that the calculated value of the ground vertical displacement by the model is much closer to the measured value than that calculated using single-layer model and the calculation error is reduced by 11.08%. The research results can provide a theoretical support for predicting ground vertical displacements caused by shield tunnelling both in single-layer soil and double-layer soil.